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android-kvm / linux / e7263e89cc995e317969f66de6b96339162350f2 / . / kernel / trace / ring_buffer.c
blob: c549a3ce05ca1ad0c18a05cf46c7cf8fe9786035 [file] [log] [blame]
// SPDX-License-Identifier: GPL-2.0
/*
* Generic ring buffer
*
* Copyright (C) 2008 Steven Rostedt <srostedt@redhat.com>
*/
#include <linux/trace_recursion.h>
#include <linux/trace_events.h>
#include <linux/ring_buffer.h>
#include <linux/trace_clock.h>
#include <linux/sched/clock.h>
#include <linux/trace_seq.h>
#include <linux/spinlock.h>
#include <linux/irq_work.h>
#include <linux/security.h>
#include <linux/uaccess.h>
#include <linux/hardirq.h>
#include <linux/kthread.h> /* for self test */
#include <linux/module.h>
#include <linux/percpu.h>
#include <linux/mutex.h>
#include <linux/delay.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/hash.h>
#include <linux/list.h>
#include <linux/cpu.h>
#include <linux/oom.h>
#include <asm/local.h>
/*
* The "absolute" timestamp in the buffer is only 59 bits.
* If a clock has the 5 MSBs set, it needs to be saved and
* reinserted.
*/
#define TS_MSB (0xf8ULL << 56)
#define ABS_TS_MASK (~TS_MSB)
static void update_pages_handler(struct work_struct *work);
/*
* The ring buffer header is special. We must manually up keep it.
*/
int ring_buffer_print_entry_header(struct trace_seq *s)
{
trace_seq_puts(s, "# compressed entry header\n");
trace_seq_puts(s, "\ttype_len : 5 bits\n");
trace_seq_puts(s, "\ttime_delta : 27 bits\n");
trace_seq_puts(s, "\tarray : 32 bits\n");
trace_seq_putc(s, '\n');
trace_seq_printf(s, "\tpadding : type == %d\n",
RINGBUF_TYPE_PADDING);
trace_seq_printf(s, "\ttime_extend : type == %d\n",
RINGBUF_TYPE_TIME_EXTEND);
trace_seq_printf(s, "\ttime_stamp : type == %d\n",
RINGBUF_TYPE_TIME_STAMP);
trace_seq_printf(s, "\tdata max type_len == %d\n",
RINGBUF_TYPE_DATA_TYPE_LEN_MAX);
return !trace_seq_has_overflowed(s);
}
/*
* The ring buffer is made up of a list of pages. A separate list of pages is
* allocated for each CPU. A writer may only write to a buffer that is
* associated with the CPU it is currently executing on. A reader may read
* from any per cpu buffer.
*
* The reader is special. For each per cpu buffer, the reader has its own
* reader page. When a reader has read the entire reader page, this reader
* page is swapped with another page in the ring buffer.
*
* Now, as long as the writer is off the reader page, the reader can do what
* ever it wants with that page. The writer will never write to that page
* again (as long as it is out of the ring buffer).
*
* Here's some silly ASCII art.
*
* +------+
* |reader| RING BUFFER
* |page |
* +------+ +---+ +---+ +---+
* | |-->| |-->| |
* +---+ +---+ +---+
* ^ |
* | |
* +---------------+
*
*
* +------+
* |reader| RING BUFFER
* |page |------------------v
* +------+ +---+ +---+ +---+
* | |-->| |-->| |
* +---+ +---+ +---+
* ^ |
* | |
* +---------------+
*
*
* +------+
* |reader| RING BUFFER
* |page |------------------v
* +------+ +---+ +---+ +---+
* ^ | |-->| |-->| |
* | +---+ +---+ +---+
* | |
* | |
* +------------------------------+
*
*
* +------+
* |buffer| RING BUFFER
* |page |------------------v
* +------+ +---+ +---+ +---+
* ^ | | | |-->| |
* | New +---+ +---+ +---+
* | Reader------^ |
* | page |
* +------------------------------+
*
*
* After we make this swap, the reader can hand this page off to the splice
* code and be done with it. It can even allocate a new page if it needs to
* and swap that into the ring buffer.
*
* We will be using cmpxchg soon to make all this lockless.
*
*/
/* Used for individual buffers (after the counter) */
#define RB_BUFFER_OFF (1 << 20)
/* define RINGBUF_TYPE_DATA for 'case RINGBUF_TYPE_DATA:' */
#define RINGBUF_TYPE_DATA 0 ... RINGBUF_TYPE_DATA_TYPE_LEN_MAX
enum {
RB_LEN_TIME_EXTEND = 8,
RB_LEN_TIME_STAMP = 8,
};
#define skip_time_extend(event) \
((struct ring_buffer_event *)((char *)event + RB_LEN_TIME_EXTEND))
#define extended_time(event) \
(event->type_len >= RINGBUF_TYPE_TIME_EXTEND)
static inline bool rb_null_event(struct ring_buffer_event *event)
{
return event->type_len == RINGBUF_TYPE_PADDING && !event->time_delta;
}
static void rb_event_set_padding(struct ring_buffer_event *event)
{
/* padding has a NULL time_delta */
event->type_len = RINGBUF_TYPE_PADDING;
event->time_delta = 0;
}
static unsigned
rb_event_data_length(struct ring_buffer_event *event)
{
unsigned length;
if (event->type_len)
length = event->type_len * RB_ALIGNMENT;
else
length = event->array[0];
return length + RB_EVNT_HDR_SIZE;
}
/*
* Return the length of the given event. Will return
* the length of the time extend if the event is a
* time extend.
*/
static inline unsigned
rb_event_length(struct ring_buffer_event *event)
{
switch (event->type_len) {
case RINGBUF_TYPE_PADDING:
if (rb_null_event(event))
/* undefined */
return -1;
return event->array[0] + RB_EVNT_HDR_SIZE;
case RINGBUF_TYPE_TIME_EXTEND:
return RB_LEN_TIME_EXTEND;
case RINGBUF_TYPE_TIME_STAMP:
return RB_LEN_TIME_STAMP;
case RINGBUF_TYPE_DATA:
return rb_event_data_length(event);
default:
WARN_ON_ONCE(1);
}
/* not hit */
return 0;
}
/*
* Return total length of time extend and data,
* or just the event length for all other events.
*/
static inline unsigned
rb_event_ts_length(struct ring_buffer_event *event)
{
unsigned len = 0;
if (extended_time(event)) {
/* time extends include the data event after it */
len = RB_LEN_TIME_EXTEND;
event = skip_time_extend(event);
}
return len + rb_event_length(event);
}
/**
* ring_buffer_event_length - return the length of the event
* @event: the event to get the length of
*
* Returns the size of the data load of a data event.
* If the event is something other than a data event, it
* returns the size of the event itself. With the exception
* of a TIME EXTEND, where it still returns the size of the
* data load of the data event after it.
*/
unsigned ring_buffer_event_length(struct ring_buffer_event *event)
{
unsigned length;
if (extended_time(event))
event = skip_time_extend(event);
length = rb_event_length(event);
if (event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
return length;
length -= RB_EVNT_HDR_SIZE;
if (length > RB_MAX_SMALL_DATA + sizeof(event->array[0]))
length -= sizeof(event->array[0]);
return length;
}
EXPORT_SYMBOL_GPL(ring_buffer_event_length);
/* inline for ring buffer fast paths */
static __always_inline void *
rb_event_data(struct ring_buffer_event *event)
{
if (extended_time(event))
event = skip_time_extend(event);
WARN_ON_ONCE(event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX);
/* If length is in len field, then array[0] has the data */
if (event->type_len)
return (void *)&event->array[0];
/* Otherwise length is in array[0] and array[1] has the data */
return (void *)&event->array[1];
}
/**
* ring_buffer_event_data - return the data of the event
* @event: the event to get the data from
*/
void *ring_buffer_event_data(struct ring_buffer_event *event)
{
return rb_event_data(event);
}
EXPORT_SYMBOL_GPL(ring_buffer_event_data);
#define for_each_buffer_cpu(buffer, cpu) \
for_each_cpu(cpu, buffer->cpumask)
#define for_each_online_buffer_cpu(buffer, cpu) \
for_each_cpu_and(cpu, buffer->cpumask, cpu_online_mask)
static u64 rb_event_time_stamp(struct ring_buffer_event *event)
{
u64 ts;
ts = event->array[0];
ts <<= TS_SHIFT;
ts += event->time_delta;
return ts;
}
/* Flag when events were overwritten */
#define RB_MISSED_EVENTS (1 << 31)
/* Missed count stored at end */
#define RB_MISSED_STORED (1 << 30)
/*
* Note, the buffer_page list must be first. The buffer pages
* are allocated in cache lines, which means that each buffer
* page will be at the beginning of a cache line, and thus
* the least significant bits will be zero. We use this to
* add flags in the list struct pointers, to make the ring buffer
* lockless.
*/
struct buffer_page {
struct list_head list; /* list of buffer pages */
local_t write; /* index for next write */
unsigned read; /* index for next read */
local_t entries; /* entries on this page */
unsigned long real_end; /* real end of data */
struct buffer_data_page *page; /* Actual data page */
u32 id; /* ID for external mapping */
};
/*
* The buffer page counters, write and entries, must be reset
* atomically when crossing page boundaries. To synchronize this
* update, two counters are inserted into the number. One is
* the actual counter for the write position or count on the page.
*
* The other is a counter of updaters. Before an update happens
* the update partition of the counter is incremented. This will
* allow the updater to update the counter atomically.
*
* The counter is 20 bits, and the state data is 12.
*/
#define RB_WRITE_MASK 0xfffff
#define RB_WRITE_INTCNT (1 << 20)
static void rb_init_page(struct buffer_data_page *bpage)
{
local_set(&bpage->commit, 0);
}
static __always_inline unsigned int rb_page_commit(struct buffer_page *bpage)
{
return local_read(&bpage->page->commit);
}
static void free_buffer_page(struct buffer_page *bpage)
{
free_page((unsigned long)bpage->page);
kfree(bpage);
}
int ring_buffer_print_page_header(struct trace_seq *s)
{
struct buffer_data_page field;
trace_seq_printf(s, "\tfield: u64 timestamp;\t"
"offset:0;\tsize:%u;\tsigned:%u;\n",
(unsigned int)sizeof(field.time_stamp),
(unsigned int)is_signed_type(u64));
trace_seq_printf(s, "\tfield: local_t commit;\t"
"offset:%u;\tsize:%u;\tsigned:%u;\n",
(unsigned int)offsetof(typeof(field), commit),
(unsigned int)sizeof(field.commit),
(unsigned int)is_signed_type(long));
trace_seq_printf(s, "\tfield: int overwrite;\t"
"offset:%u;\tsize:%u;\tsigned:%u;\n",
(unsigned int)offsetof(typeof(field), commit),
1,
(unsigned int)is_signed_type(long));
trace_seq_printf(s, "\tfield: char data;\t"
"offset:%u;\tsize:%u;\tsigned:%u;\n",
(unsigned int)offsetof(typeof(field), data),
(unsigned int)BUF_PAGE_SIZE,
(unsigned int)is_signed_type(char));
return !trace_seq_has_overflowed(s);
}
struct rb_irq_work {
struct irq_work work;
wait_queue_head_t waiters;
wait_queue_head_t full_waiters;
long wait_index;
bool waiters_pending;
bool full_waiters_pending;
bool wakeup_full;
};
/*
* Structure to hold event state and handle nested events.
*/
struct rb_event_info {
u64 ts;
u64 delta;
u64 before;
u64 after;
unsigned long length;
struct buffer_page *tail_page;
int add_timestamp;
};
/*
* Used for the add_timestamp
* NONE
* EXTEND - wants a time extend
* ABSOLUTE - the buffer requests all events to have absolute time stamps
* FORCE - force a full time stamp.
*/
enum {
RB_ADD_STAMP_NONE = 0,
RB_ADD_STAMP_EXTEND = BIT(1),
RB_ADD_STAMP_ABSOLUTE = BIT(2),
RB_ADD_STAMP_FORCE = BIT(3)
};
/*
* Used for which event context the event is in.
* TRANSITION = 0
* NMI = 1
* IRQ = 2
* SOFTIRQ = 3
* NORMAL = 4
*
* See trace_recursive_lock() comment below for more details.
*/
enum {
RB_CTX_TRANSITION,
RB_CTX_NMI,
RB_CTX_IRQ,
RB_CTX_SOFTIRQ,
RB_CTX_NORMAL,
RB_CTX_MAX
};
#if BITS_PER_LONG == 32
#define RB_TIME_32
#endif
/* To test on 64 bit machines */
//#define RB_TIME_32
#ifdef RB_TIME_32
struct rb_time_struct {
local_t cnt;
local_t top;
local_t bottom;
local_t msb;
};
#else
#include <asm/local64.h>
struct rb_time_struct {
local64_t time;
};
#endif
typedef struct rb_time_struct rb_time_t;
#define MAX_NEST 5
/*
* head_page == tail_page && head == tail then buffer is empty.
*/
struct ring_buffer_per_cpu {
int cpu;
atomic_t record_disabled;
atomic_t resize_disabled;
struct trace_buffer *buffer;
raw_spinlock_t reader_lock; /* serialize readers */
arch_spinlock_t lock;
struct lock_class_key lock_key;
struct buffer_data_page *free_page;
unsigned long nr_pages;
unsigned int current_context;
struct list_head *pages;
struct buffer_page *head_page; /* read from head */
struct buffer_page *tail_page; /* write to tail */
struct buffer_page *commit_page; /* committed pages */
struct buffer_page *reader_page;
unsigned long lost_events;
unsigned long last_overrun;
unsigned long nest;
local_t entries_bytes;
local_t entries;
local_t overrun;
local_t commit_overrun;
local_t dropped_events;
local_t committing;
local_t commits;
local_t pages_touched;
local_t pages_lost;
local_t pages_read;
long last_pages_touch;
size_t shortest_full;
unsigned long read;
unsigned long read_bytes;
rb_time_t write_stamp;
rb_time_t before_stamp;
u64 event_stamp[MAX_NEST];
u64 read_stamp;
/* pages removed since last reset */
unsigned long pages_removed;
int mapped;
struct mutex mapping_lock;
unsigned long *page_ids; /* ID to addr */
struct ring_buffer_meta *meta_page;
struct ring_buffer_writer *writer;
/* ring buffer pages to update, > 0 to add, < 0 to remove */
long nr_pages_to_update;
struct list_head new_pages; /* new pages to add */
struct work_struct update_pages_work;
struct completion update_done;
struct rb_irq_work irq_work;
};
struct trace_buffer {
unsigned flags;
int cpus;
atomic_t record_disabled;
atomic_t resizing;
cpumask_var_t cpumask;
struct lock_class_key *reader_lock_key;
struct mutex mutex;
struct ring_buffer_per_cpu **buffers;
struct ring_buffer_writer *writer;
struct hlist_node node;
u64 (*clock)(void);
struct rb_irq_work irq_work;
bool time_stamp_abs;
};
struct ring_buffer_iter {
struct ring_buffer_per_cpu *cpu_buffer;
unsigned long head;
unsigned long next_event;
struct buffer_page *head_page;
struct buffer_page *cache_reader_page;
unsigned long cache_read;
unsigned long cache_pages_removed;
u64 read_stamp;
u64 page_stamp;
struct ring_buffer_event *event;
int missed_events;
};
#ifdef RB_TIME_32
/*
* On 32 bit machines, local64_t is very expensive. As the ring
* buffer doesn't need all the features of a true 64 bit atomic,
* on 32 bit, it uses these functions (64 still uses local64_t).
*
* For the ring buffer, 64 bit required operations for the time is
* the following:
*
* - Reads may fail if it interrupted a modification of the time stamp.
* It will succeed if it did not interrupt another write even if
* the read itself is interrupted by a write.
* It returns whether it was successful or not.
*
* - Writes always succeed and will overwrite other writes and writes
* that were done by events interrupting the current write.
*
* - A write followed by a read of the same time stamp will always succeed,
* but may not contain the same value.
*
* - A cmpxchg will fail if it interrupted another write or cmpxchg.
* Other than that, it acts like a normal cmpxchg.
*
* The 60 bit time stamp is broken up by 30 bits in a top and bottom half
* (bottom being the least significant 30 bits of the 60 bit time stamp).
*
* The two most significant bits of each half holds a 2 bit counter (0-3).
* Each update will increment this counter by one.
* When reading the top and bottom, if the two counter bits match then the
* top and bottom together make a valid 60 bit number.
*/
#define RB_TIME_SHIFT 30
#define RB_TIME_VAL_MASK ((1 << RB_TIME_SHIFT) - 1)
#define RB_TIME_MSB_SHIFT 60
static inline int rb_time_cnt(unsigned long val)
{
return (val >> RB_TIME_SHIFT) & 3;
}
static inline u64 rb_time_val(unsigned long top, unsigned long bottom)
{
u64 val;
val = top & RB_TIME_VAL_MASK;
val <<= RB_TIME_SHIFT;
val |= bottom & RB_TIME_VAL_MASK;
return val;
}
static inline bool __rb_time_read(rb_time_t *t, u64 *ret, unsigned long *cnt)
{
unsigned long top, bottom, msb;
unsigned long c;
/*
* If the read is interrupted by a write, then the cnt will
* be different. Loop until both top and bottom have been read
* without interruption.
*/
do {
c = local_read(&t->cnt);
top = local_read(&t->top);
bottom = local_read(&t->bottom);
msb = local_read(&t->msb);
} while (c != local_read(&t->cnt));
*cnt = rb_time_cnt(top);
/* If top, msb or bottom counts don't match, this interrupted a write */
if (*cnt != rb_time_cnt(msb) || *cnt != rb_time_cnt(bottom))
return false;
/* The shift to msb will lose its cnt bits */
*ret = rb_time_val(top, bottom) | ((u64)msb << RB_TIME_MSB_SHIFT);
return true;
}
static bool rb_time_read(rb_time_t *t, u64 *ret)
{
unsigned long cnt;
return __rb_time_read(t, ret, &cnt);
}
static inline unsigned long rb_time_val_cnt(unsigned long val, unsigned long cnt)
{
return (val & RB_TIME_VAL_MASK) | ((cnt & 3) << RB_TIME_SHIFT);
}
static inline void rb_time_split(u64 val, unsigned long *top, unsigned long *bottom,
unsigned long *msb)
{
*top = (unsigned long)((val >> RB_TIME_SHIFT) & RB_TIME_VAL_MASK);
*bottom = (unsigned long)(val & RB_TIME_VAL_MASK);
*msb = (unsigned long)(val >> RB_TIME_MSB_SHIFT);
}
static inline void rb_time_val_set(local_t *t, unsigned long val, unsigned long cnt)
{
val = rb_time_val_cnt(val, cnt);
local_set(t, val);
}
static void rb_time_set(rb_time_t *t, u64 val)
{
unsigned long cnt, top, bottom, msb;
rb_time_split(val, &top, &bottom, &msb);
/* Writes always succeed with a valid number even if it gets interrupted. */
do {
cnt = local_inc_return(&t->cnt);
rb_time_val_set(&t->top, top, cnt);
rb_time_val_set(&t->bottom, bottom, cnt);
rb_time_val_set(&t->msb, val >> RB_TIME_MSB_SHIFT, cnt);
} while (cnt != local_read(&t->cnt));
}
static inline bool
rb_time_read_cmpxchg(local_t *l, unsigned long expect, unsigned long set)
{
return local_try_cmpxchg(l, &expect, set);
}
#else /* 64 bits */
/* local64_t always succeeds */
static inline bool rb_time_read(rb_time_t *t, u64 *ret)
{
*ret = local64_read(&t->time);
return true;
}
static void rb_time_set(rb_time_t *t, u64 val)
{
local64_set(&t->time, val);
}
#endif
/*
* Enable this to make sure that the event passed to
* ring_buffer_event_time_stamp() is not committed and also
* is on the buffer that it passed in.
*/
//#define RB_VERIFY_EVENT
#ifdef RB_VERIFY_EVENT
static struct list_head *rb_list_head(struct list_head *list);
static void verify_event(struct ring_buffer_per_cpu *cpu_buffer,
void *event)
{
struct buffer_page *page = cpu_buffer->commit_page;
struct buffer_page *tail_page = READ_ONCE(cpu_buffer->tail_page);
struct list_head *next;
long commit, write;
unsigned long addr = (unsigned long)event;
bool done = false;
int stop = 0;
/* Make sure the event exists and is not committed yet */
do {
if (page == tail_page || WARN_ON_ONCE(stop++ > 100))
done = true;
commit = local_read(&page->page->commit);
write = local_read(&page->write);
if (addr >= (unsigned long)&page->page->data[commit] &&
addr < (unsigned long)&page->page->data[write])
return;
next = rb_list_head(page->list.next);
page = list_entry(next, struct buffer_page, list);
} while (!done);
WARN_ON_ONCE(1);
}
#else
static inline void verify_event(struct ring_buffer_per_cpu *cpu_buffer,
void *event)
{
}
#endif
/*
* The absolute time stamp drops the 5 MSBs and some clocks may
* require them. The rb_fix_abs_ts() will take a previous full
* time stamp, and add the 5 MSB of that time stamp on to the
* saved absolute time stamp. Then they are compared in case of
* the unlikely event that the latest time stamp incremented
* the 5 MSB.
*/
static inline u64 rb_fix_abs_ts(u64 abs, u64 save_ts)
{
if (save_ts & TS_MSB) {
abs |= save_ts & TS_MSB;
/* Check for overflow */
if (unlikely(abs < save_ts))
abs += 1ULL << 59;
}
return abs;
}
static inline u64 rb_time_stamp(struct trace_buffer *buffer);
/**
* ring_buffer_event_time_stamp - return the event's current time stamp
* @buffer: The buffer that the event is on
* @event: the event to get the time stamp of
*
* Note, this must be called after @event is reserved, and before it is
* committed to the ring buffer. And must be called from the same
* context where the event was reserved (normal, softirq, irq, etc).
*
* Returns the time stamp associated with the current event.
* If the event has an extended time stamp, then that is used as
* the time stamp to return.
* In the highly unlikely case that the event was nested more than
* the max nesting, then the write_stamp of the buffer is returned,
* otherwise current time is returned, but that really neither of
* the last two cases should ever happen.
*/
u64 ring_buffer_event_time_stamp(struct trace_buffer *buffer,
struct ring_buffer_event *event)
{
struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[smp_processor_id()];
unsigned int nest;
u64 ts;
/* If the event includes an absolute time, then just use that */
if (event->type_len == RINGBUF_TYPE_TIME_STAMP) {
ts = rb_event_time_stamp(event);
return rb_fix_abs_ts(ts, cpu_buffer->tail_page->page->time_stamp);
}
nest = local_read(&cpu_buffer->committing);
verify_event(cpu_buffer, event);
if (WARN_ON_ONCE(!nest))
goto fail;
/* Read the current saved nesting level time stamp */
if (likely(--nest < MAX_NEST))
return cpu_buffer->event_stamp[nest];
/* Shouldn't happen, warn if it does */
WARN_ONCE(1, "nest (%d) greater than max", nest);
fail:
/* Can only fail on 32 bit */
if (!rb_time_read(&cpu_buffer->write_stamp, &ts))
/* Screw it, just read the current time */
ts = rb_time_stamp(cpu_buffer->buffer);
return ts;
}
/**
* ring_buffer_nr_pages - get the number of buffer pages in the ring buffer
* @buffer: The ring_buffer to get the number of pages from
* @cpu: The cpu of the ring_buffer to get the number of pages from
*
* Returns the number of pages used by a per_cpu buffer of the ring buffer.
*/
size_t ring_buffer_nr_pages(struct trace_buffer *buffer, int cpu)
{
return buffer->buffers[cpu]->nr_pages;
}
/**
* ring_buffer_nr_dirty_pages - get the number of used pages in the ring buffer
* @buffer: The ring_buffer to get the number of pages from
* @cpu: The cpu of the ring_buffer to get the number of pages from
*
* Returns the number of pages that have content in the ring buffer.
*/
size_t ring_buffer_nr_dirty_pages(struct trace_buffer *buffer, int cpu)
{
size_t read;
size_t lost;
size_t cnt;
read = local_read(&buffer->buffers[cpu]->pages_read);
lost = local_read(&buffer->buffers[cpu]->pages_lost);
cnt = local_read(&buffer->buffers[cpu]->pages_touched);
if (WARN_ON_ONCE(cnt < lost))
return 0;
cnt -= lost;
/* The reader can read an empty page, but not more than that */
if (cnt < read) {
WARN_ON_ONCE(read > cnt + 1);
return 0;
}
return cnt - read;
}
static __always_inline bool full_hit(struct trace_buffer *buffer, int cpu, int full)
{
struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
size_t nr_pages;
size_t dirty;
nr_pages = cpu_buffer->nr_pages;
if (!nr_pages || !full)
return true;
/*
* Add one as dirty will never equal nr_pages, as the sub-buffer
* that the writer is on is not counted as dirty.
* This is needed if "buffer_percent" is set to 100.
*/
dirty = ring_buffer_nr_dirty_pages(buffer, cpu) + 1;
return (dirty * 100) >= (full * nr_pages);
}
/*
* rb_wake_up_waiters - wake up tasks waiting for ring buffer input
*
* Schedules a delayed work to wake up any task that is blocked on the
* ring buffer waiters queue.
*/
static void rb_wake_up_waiters(struct irq_work *work)
{
struct rb_irq_work *rbwork = container_of(work, struct rb_irq_work, work);
wake_up_all(&rbwork->waiters);
if (rbwork->full_waiters_pending || rbwork->wakeup_full) {
rbwork->wakeup_full = false;
rbwork->full_waiters_pending = false;
wake_up_all(&rbwork->full_waiters);
}
}
/**
* ring_buffer_wake_waiters - wake up any waiters on this ring buffer
* @buffer: The ring buffer to wake waiters on
* @cpu: The CPU buffer to wake waiters on
*
* In the case of a file that represents a ring buffer is closing,
* it is prudent to wake up any waiters that are on this.
*/
void ring_buffer_wake_waiters(struct trace_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
struct rb_irq_work *rbwork;
if (!buffer)
return;
if (cpu == RING_BUFFER_ALL_CPUS) {
/* Wake up individual ones too. One level recursion */
for_each_buffer_cpu(buffer, cpu)
ring_buffer_wake_waiters(buffer, cpu);
rbwork = &buffer->irq_work;
} else {
if (WARN_ON_ONCE(!buffer->buffers))
return;
if (WARN_ON_ONCE(cpu >= nr_cpu_ids))
return;
cpu_buffer = buffer->buffers[cpu];
/* The CPU buffer may not have been initialized yet */
if (!cpu_buffer)
return;
rbwork = &cpu_buffer->irq_work;
}
rbwork->wait_index++;
/* make sure the waiters see the new index */
smp_wmb();
/* This can be called in any context */
irq_work_queue(&rbwork->work);
}
/**
* ring_buffer_wait - wait for input to the ring buffer
* @buffer: buffer to wait on
* @cpu: the cpu buffer to wait on
* @full: wait until the percentage of pages are available, if @cpu != RING_BUFFER_ALL_CPUS
*
* If @cpu == RING_BUFFER_ALL_CPUS then the task will wake up as soon
* as data is added to any of the @buffer's cpu buffers. Otherwise
* it will wait for data to be added to a specific cpu buffer.
*/
int ring_buffer_wait(struct trace_buffer *buffer, int cpu, int full)
{
struct ring_buffer_per_cpu *cpu_buffer;
DEFINE_WAIT(wait);
struct rb_irq_work *work;
long wait_index;
int ret = 0;
/*
* Depending on what the caller is waiting for, either any
* data in any cpu buffer, or a specific buffer, put the
* caller on the appropriate wait queue.
*/
if (cpu == RING_BUFFER_ALL_CPUS) {
work = &buffer->irq_work;
/* Full only makes sense on per cpu reads */
full = 0;
} else {
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return -ENODEV;
cpu_buffer = buffer->buffers[cpu];
work = &cpu_buffer->irq_work;
}
wait_index = READ_ONCE(work->wait_index);
while (true) {
if (full)
prepare_to_wait(&work->full_waiters, &wait, TASK_INTERRUPTIBLE);
else
prepare_to_wait(&work->waiters, &wait, TASK_INTERRUPTIBLE);
/*
* The events can happen in critical sections where
* checking a work queue can cause deadlocks.
* After adding a task to the queue, this flag is set
* only to notify events to try to wake up the queue
* using irq_work.
*
* We don't clear it even if the buffer is no longer
* empty. The flag only causes the next event to run
* irq_work to do the work queue wake up. The worse
* that can happen if we race with !trace_empty() is that
* an event will cause an irq_work to try to wake up
* an empty queue.
*
* There's no reason to protect this flag either, as
* the work queue and irq_work logic will do the necessary
* synchronization for the wake ups. The only thing
* that is necessary is that the wake up happens after
* a task has been queued. It's OK for spurious wake ups.
*/
if (full)
work->full_waiters_pending = true;
else
work->waiters_pending = true;
if (signal_pending(current)) {
ret = -EINTR;
break;
}
if (cpu == RING_BUFFER_ALL_CPUS && !ring_buffer_empty(buffer))
break;
if (cpu != RING_BUFFER_ALL_CPUS &&
!ring_buffer_empty_cpu(buffer, cpu)) {
unsigned long flags;
bool pagebusy;
bool done;
if (!full)
break;
raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
pagebusy = cpu_buffer->reader_page == cpu_buffer->commit_page;
done = !pagebusy && full_hit(buffer, cpu, full);
if (!cpu_buffer->shortest_full ||
cpu_buffer->shortest_full > full)
cpu_buffer->shortest_full = full;
raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
if (done)
break;
}
schedule();
/* Make sure to see the new wait index */
smp_rmb();
if (wait_index != work->wait_index)
break;
}
if (full)
finish_wait(&work->full_waiters, &wait);
else
finish_wait(&work->waiters, &wait);
return ret;
}
/**
* ring_buffer_poll_wait - poll on buffer input
* @buffer: buffer to wait on
* @cpu: the cpu buffer to wait on
* @filp: the file descriptor
* @poll_table: The poll descriptor
* @full: wait until the percentage of pages are available, if @cpu != RING_BUFFER_ALL_CPUS
*
* If @cpu == RING_BUFFER_ALL_CPUS then the task will wake up as soon
* as data is added to any of the @buffer's cpu buffers. Otherwise
* it will wait for data to be added to a specific cpu buffer.
*
* Returns EPOLLIN | EPOLLRDNORM if data exists in the buffers,
* zero otherwise.
*/
__poll_t ring_buffer_poll_wait(struct trace_buffer *buffer, int cpu,
struct file *filp, poll_table *poll_table, int full)
{
struct ring_buffer_per_cpu *cpu_buffer;
struct rb_irq_work *work;
if (cpu == RING_BUFFER_ALL_CPUS) {
work = &buffer->irq_work;
full = 0;
} else {
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return -EINVAL;
cpu_buffer = buffer->buffers[cpu];
work = &cpu_buffer->irq_work;
}
if (full) {
poll_wait(filp, &work->full_waiters, poll_table);
work->full_waiters_pending = true;
if (!cpu_buffer->shortest_full ||
cpu_buffer->shortest_full > full)
cpu_buffer->shortest_full = full;
} else {
poll_wait(filp, &work->waiters, poll_table);
work->waiters_pending = true;
}
/*
* There's a tight race between setting the waiters_pending and
* checking if the ring buffer is empty. Once the waiters_pending bit
* is set, the next event will wake the task up, but we can get stuck
* if there's only a single event in.
*
* FIXME: Ideally, we need a memory barrier on the writer side as well,
* but adding a memory barrier to all events will cause too much of a
* performance hit in the fast path. We only need a memory barrier when
* the buffer goes from empty to having content. But as this race is
* extremely small, and it's not a problem if another event comes in, we
* will fix it later.
*/
smp_mb();
if (full)
return full_hit(buffer, cpu, full) ? EPOLLIN | EPOLLRDNORM : 0;
if ((cpu == RING_BUFFER_ALL_CPUS && !ring_buffer_empty(buffer)) ||
(cpu != RING_BUFFER_ALL_CPUS && !ring_buffer_empty_cpu(buffer, cpu)))
return EPOLLIN | EPOLLRDNORM;
return 0;
}
/* buffer may be either ring_buffer or ring_buffer_per_cpu */
#define RB_WARN_ON(b, cond) \
({ \
int _____ret = unlikely(cond); \
if (_____ret) { \
if (__same_type(*(b), struct ring_buffer_per_cpu)) { \
struct ring_buffer_per_cpu *__b = \
(void *)b; \
atomic_inc(&__b->buffer->record_disabled); \
} else \
atomic_inc(&b->record_disabled); \
WARN_ON(1); \
} \
_____ret; \
})
/* Up this if you want to test the TIME_EXTENTS and normalization */
#define DEBUG_SHIFT 0
static inline u64 rb_time_stamp(struct trace_buffer *buffer)
{
u64 ts;
/* Skip retpolines :-( */
if (IS_ENABLED(CONFIG_RETPOLINE) && likely(buffer->clock == trace_clock_local))
ts = trace_clock_local();
else
ts = buffer->clock();
/* shift to debug/test normalization and TIME_EXTENTS */
return ts << DEBUG_SHIFT;
}
u64 ring_buffer_time_stamp(struct trace_buffer *buffer)
{
u64 time;
preempt_disable_notrace();
time = rb_time_stamp(buffer);
preempt_enable_notrace();
return time;
}
EXPORT_SYMBOL_GPL(ring_buffer_time_stamp);
void ring_buffer_normalize_time_stamp(struct trace_buffer *buffer,
int cpu, u64 *ts)
{
/* Just stupid testing the normalize function and deltas */
*ts >>= DEBUG_SHIFT;
}
EXPORT_SYMBOL_GPL(ring_buffer_normalize_time_stamp);
/*
* Making the ring buffer lockless makes things tricky.
* Although writes only happen on the CPU that they are on,
* and they only need to worry about interrupts. Reads can
* happen on any CPU.
*
* The reader page is always off the ring buffer, but when the
* reader finishes with a page, it needs to swap its page with
* a new one from the buffer. The reader needs to take from
* the head (writes go to the tail). But if a writer is in overwrite
* mode and wraps, it must push the head page forward.
*
* Here lies the problem.
*
* The reader must be careful to replace only the head page, and
* not another one. As described at the top of the file in the
* ASCII art, the reader sets its old page to point to the next
* page after head. It then sets the page after head to point to
* the old reader page. But if the writer moves the head page
* during this operation, the reader could end up with the tail.
*
* We use cmpxchg to help prevent this race. We also do something
* special with the page before head. We set the LSB to 1.
*
* When the writer must push the page forward, it will clear the
* bit that points to the head page, move the head, and then set
* the bit that points to the new head page.
*
* We also don't want an interrupt coming in and moving the head
* page on another writer. Thus we use the second LSB to catch
* that too. Thus:
*
* head->list->prev->next bit 1 bit 0
* ------- -------
* Normal page 0 0
* Points to head page 0 1
* New head page 1 0
*
* Note we can not trust the prev pointer of the head page, because:
*
* +----+ +-----+ +-----+
* | |------>| T |---X--->| N |
* | |<------| | | |
* +----+ +-----+ +-----+
* ^ ^ |
* | +-----+ | |
* +----------| R |----------+ |
* | |<-----------+
* +-----+
*
* Key: ---X--> HEAD flag set in pointer
* T Tail page
* R Reader page
* N Next page
*
* (see __rb_reserve_next() to see where this happens)
*
* What the above shows is that the reader just swapped out
* the reader page with a page in the buffer, but before it
* could make the new header point back to the new page added
* it was preempted by a writer. The writer moved forward onto
* the new page added by the reader and is about to move forward
* again.
*
* You can see, it is legitimate for the previous pointer of
* the head (or any page) not to point back to itself. But only
* temporarily.
*/
#define RB_PAGE_NORMAL 0UL
#define RB_PAGE_HEAD 1UL
#define RB_PAGE_UPDATE 2UL
#define RB_FLAG_MASK 3UL
/* PAGE_MOVED is not part of the mask */
#define RB_PAGE_MOVED 4UL
/*
* rb_list_head - remove any bit
*/
static struct list_head *rb_list_head(struct list_head *list)
{
unsigned long val = (unsigned long)list;
return (struct list_head *)(val & ~RB_FLAG_MASK);
}
/*
* rb_is_head_page - test if the given page is the head page
*
* Because the reader may move the head_page pointer, we can
* not trust what the head page is (it may be pointing to
* the reader page). But if the next page is a header page,
* its flags will be non zero.
*/
static inline int
rb_is_head_page(struct buffer_page *page, struct list_head *list)
{
unsigned long val;
val = (unsigned long)list->next;
if ((val & ~RB_FLAG_MASK) != (unsigned long)&page->list)
return RB_PAGE_MOVED;
return val & RB_FLAG_MASK;
}
/*
* rb_is_reader_page
*
* The unique thing about the reader page, is that, if the
* writer is ever on it, the previous pointer never points
* back to the reader page.
*/
static bool rb_is_reader_page(struct buffer_page *page)
{
struct list_head *list = page->list.prev;
return rb_list_head(list->next) != &page->list;
}
/*
* rb_set_list_to_head - set a list_head to be pointing to head.
*/
static void rb_set_list_to_head(struct list_head *list)
{
unsigned long *ptr;
ptr = (unsigned long *)&list->next;
*ptr |= RB_PAGE_HEAD;
*ptr &= ~RB_PAGE_UPDATE;
}
/*
* rb_head_page_activate - sets up head page
*/
static void rb_head_page_activate(struct ring_buffer_per_cpu *cpu_buffer)
{
struct buffer_page *head;
head = cpu_buffer->head_page;
if (!head)
return;
/*
* Set the previous list pointer to have the HEAD flag.
*/
rb_set_list_to_head(head->list.prev);
}
static void rb_list_head_clear(struct list_head *list)
{
unsigned long *ptr = (unsigned long *)&list->next;
*ptr &= ~RB_FLAG_MASK;
}
/*
* rb_head_page_deactivate - clears head page ptr (for free list)
*/
static void
rb_head_page_deactivate(struct ring_buffer_per_cpu *cpu_buffer)
{
struct list_head *hd;
/* Go through the whole list and clear any pointers found. */
rb_list_head_clear(cpu_buffer->pages);
list_for_each(hd, cpu_buffer->pages)
rb_list_head_clear(hd);
}
static int rb_head_page_set(struct ring_buffer_per_cpu *cpu_buffer,
struct buffer_page *head,
struct buffer_page *prev,
int old_flag, int new_flag)
{
struct list_head *list;
unsigned long val = (unsigned long)&head->list;
unsigned long ret;
list = &prev->list;
val &= ~RB_FLAG_MASK;
ret = cmpxchg((unsigned long *)&list->next,
val | old_flag, val | new_flag);
/* check if the reader took the page */
if ((ret & ~RB_FLAG_MASK) != val)
return RB_PAGE_MOVED;
return ret & RB_FLAG_MASK;
}
static int rb_head_page_set_update(struct ring_buffer_per_cpu *cpu_buffer,
struct buffer_page *head,
struct buffer_page *prev,
int old_flag)
{
return rb_head_page_set(cpu_buffer, head, prev,
old_flag, RB_PAGE_UPDATE);
}
static int rb_head_page_set_head(struct ring_buffer_per_cpu *cpu_buffer,
struct buffer_page *head,
struct buffer_page *prev,
int old_flag)
{
return rb_head_page_set(cpu_buffer, head, prev,
old_flag, RB_PAGE_HEAD);
}
static int rb_head_page_set_normal(struct ring_buffer_per_cpu *cpu_buffer,
struct buffer_page *head,
struct buffer_page *prev,
int old_flag)
{
return rb_head_page_set(cpu_buffer, head, prev,
old_flag, RB_PAGE_NORMAL);
}
static inline void rb_inc_page(struct buffer_page **bpage)
{
struct list_head *p = rb_list_head((*bpage)->list.next);
*bpage = list_entry(p, struct buffer_page, list);
}
static struct buffer_page *
rb_set_head_page(struct ring_buffer_per_cpu *cpu_buffer)
{
struct buffer_page *head;
struct buffer_page *page;
struct list_head *list;
int i;
if (RB_WARN_ON(cpu_buffer, !cpu_buffer->head_page))
return NULL;
/* sanity check */
list = cpu_buffer->pages;
if (RB_WARN_ON(cpu_buffer, rb_list_head(list->prev->next) != list))
return NULL;
page = head = cpu_buffer->head_page;
/*
* It is possible that the writer moves the header behind
* where we started, and we miss in one loop.
* A second loop should grab the header, but we'll do
* three loops just because I'm paranoid.
*/
for (i = 0; i < 3; i++) {
do {
if (rb_is_head_page(page, page->list.prev)) {
cpu_buffer->head_page = page;
return page;
}
rb_inc_page(&page);
} while (page != head);
}
RB_WARN_ON(cpu_buffer, 1);
return NULL;
}
static bool rb_head_page_replace(struct buffer_page *old,
struct buffer_page *new)
{
unsigned long *ptr = (unsigned long *)&old->list.prev->next;
unsigned long val;
val = *ptr & ~RB_FLAG_MASK;
val |= RB_PAGE_HEAD;
return try_cmpxchg(ptr, &val, (unsigned long)&new->list);
}
/*
* rb_tail_page_update - move the tail page forward
*/
static void rb_tail_page_update(struct ring_buffer_per_cpu *cpu_buffer,
struct buffer_page *tail_page,
struct buffer_page *next_page)
{
unsigned long old_entries;
unsigned long old_write;
/*
* The tail page now needs to be moved forward.
*
* We need to reset the tail page, but without messing
* with possible erasing of data brought in by interrupts
* that have moved the tail page and are currently on it.
*
* We add a counter to the write field to denote this.
*/
old_write = local_add_return(RB_WRITE_INTCNT, &next_page->write);
old_entries = local_add_return(RB_WRITE_INTCNT, &next_page->entries);
local_inc(&cpu_buffer->pages_touched);
/*
* Just make sure we have seen our old_write and synchronize
* with any interrupts that come in.
*/
barrier();
/*
* If the tail page is still the same as what we think
* it is, then it is up to us to update the tail
* pointer.
*/
if (tail_page == READ_ONCE(cpu_buffer->tail_page)) {
/* Zero the write counter */
unsigned long val = old_write & ~RB_WRITE_MASK;
unsigned long eval = old_entries & ~RB_WRITE_MASK;
/*
* This will only succeed if an interrupt did
* not come in and change it. In which case, we
* do not want to modify it.
*
* We add (void) to let the compiler know that we do not care
* about the return value of these functions. We use the
* cmpxchg to only update if an interrupt did not already
* do it for us. If the cmpxchg fails, we don't care.
*/
(void)local_cmpxchg(&next_page->write, old_write, val);
(void)local_cmpxchg(&next_page->entries, old_entries, eval);
/*
* No need to worry about races with clearing out the commit.
* it only can increment when a commit takes place. But that
* only happens in the outer most nested commit.
*/
local_set(&next_page->page->commit, 0);
/* Again, either we update tail_page or an interrupt does */
(void)cmpxchg(&cpu_buffer->tail_page, tail_page, next_page);
}
if (READ_ONCE(cpu_buffer->mapped)) {
/* Ensure the meta_page is ready */
smp_rmb();
WRITE_ONCE(cpu_buffer->meta_page->pages_touched,
local_read(&cpu_buffer->pages_touched));
}
}
static void rb_check_bpage(struct ring_buffer_per_cpu *cpu_buffer,
struct buffer_page *bpage)
{
unsigned long val = (unsigned long)bpage;
RB_WARN_ON(cpu_buffer, val & RB_FLAG_MASK);
}
/**
* rb_check_pages - integrity check of buffer pages
* @cpu_buffer: CPU buffer with pages to test
*
* As a safety measure we check to make sure the data pages have not
* been corrupted.
*/
static void rb_check_pages(struct ring_buffer_per_cpu *cpu_buffer)
{
struct list_head *head = rb_list_head(cpu_buffer->pages);
struct list_head *tmp;
if (RB_WARN_ON(cpu_buffer,
rb_list_head(rb_list_head(head->next)->prev) != head))
return;
if (RB_WARN_ON(cpu_buffer,
rb_list_head(rb_list_head(head->prev)->next) != head))
return;
for (tmp = rb_list_head(head->next); tmp != head; tmp = rb_list_head(tmp->next)) {
if (RB_WARN_ON(cpu_buffer,
rb_list_head(rb_list_head(tmp->next)->prev) != tmp))
return;
if (RB_WARN_ON(cpu_buffer,
rb_list_head(rb_list_head(tmp->prev)->next) != tmp))
return;
}
}
static int __rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
long nr_pages, struct list_head *pages)
{
struct buffer_page *bpage, *tmp;
bool user_thread = current->mm != NULL;
gfp_t mflags;
long i;
/*
* Check if the available memory is there first.
* Note, si_mem_available() only gives us a rough estimate of available
* memory. It may not be accurate. But we don't care, we just want
* to prevent doing any allocation when it is obvious that it is
* not going to succeed.
*/
i = si_mem_available();
if (i < nr_pages)
return -ENOMEM;
/*
* __GFP_RETRY_MAYFAIL flag makes sure that the allocation fails
* gracefully without invoking oom-killer and the system is not
* destabilized.
*/
mflags = GFP_KERNEL | __GFP_RETRY_MAYFAIL;
/*
* If a user thread allocates too much, and si_mem_available()
* reports there's enough memory, even though there is not.
* Make sure the OOM killer kills this thread. This can happen
* even with RETRY_MAYFAIL because another task may be doing
* an allocation after this task has taken all memory.
* This is the task the OOM killer needs to take out during this
* loop, even if it was triggered by an allocation somewhere else.
*/
if (user_thread)
set_current_oom_origin();
for (i = 0; i < nr_pages; i++) {
struct page *page;
bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
mflags, cpu_to_node(cpu_buffer->cpu));
if (!bpage)
goto free_pages;
rb_check_bpage(cpu_buffer, bpage);
list_add(&bpage->list, pages);
page = alloc_pages_node(cpu_to_node(cpu_buffer->cpu), mflags, 0);
if (!page)
goto free_pages;
bpage->page = page_address(page);
rb_init_page(bpage->page);
if (user_thread && fatal_signal_pending(current))
goto free_pages;
}
if (user_thread)
clear_current_oom_origin();
return 0;
free_pages:
list_for_each_entry_safe(bpage, tmp, pages, list) {
list_del_init(&bpage->list);
free_buffer_page(bpage);
}
if (user_thread)
clear_current_oom_origin();
return -ENOMEM;
}
static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
unsigned long nr_pages)
{
LIST_HEAD(pages);
WARN_ON(!nr_pages);
if (__rb_allocate_pages(cpu_buffer, nr_pages, &pages))
return -ENOMEM;
/*
* The ring buffer page list is a circular list that does not
* start and end with a list head. All page list items point to
* other pages.
*/
cpu_buffer->pages = pages.next;
list_del(&pages);
cpu_buffer->nr_pages = nr_pages;
rb_check_pages(cpu_buffer);
return 0;
}
static struct ring_buffer_per_cpu *
rb_allocate_cpu_buffer(struct trace_buffer *buffer, long nr_pages, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
struct buffer_page *bpage;
struct page *page;
int ret;
cpu_buffer = kzalloc_node(ALIGN(sizeof(*cpu_buffer), cache_line_size()),
GFP_KERNEL, cpu_to_node(cpu));
if (!cpu_buffer)
return NULL;
cpu_buffer->cpu = cpu;
cpu_buffer->buffer = buffer;
raw_spin_lock_init(&cpu_buffer->reader_lock);
lockdep_set_class(&cpu_buffer->reader_lock, buffer->reader_lock_key);
cpu_buffer->lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
INIT_WORK(&cpu_buffer->update_pages_work, update_pages_handler);
init_completion(&cpu_buffer->update_done);
init_irq_work(&cpu_buffer->irq_work.work, rb_wake_up_waiters);
init_waitqueue_head(&cpu_buffer->irq_work.waiters);
init_waitqueue_head(&cpu_buffer->irq_work.full_waiters);
mutex_init(&cpu_buffer->mapping_lock);
bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
GFP_KERNEL, cpu_to_node(cpu));
if (!bpage)
goto fail_free_buffer;
rb_check_bpage(cpu_buffer, bpage);
cpu_buffer->reader_page = bpage;
if (buffer->writer) {
struct rb_page_desc *pdesc = rb_page_desc(buffer->writer->pdesc, cpu);
if (!pdesc)
goto fail_free_reader;
cpu_buffer->writer = buffer->writer;
cpu_buffer->meta_page = (struct ring_buffer_meta *)(void *)pdesc->meta_va;
cpu_buffer->page_ids = pdesc->page_va;
cpu_buffer->nr_pages = pdesc->nr_page_va - 1;
atomic_inc(&cpu_buffer->record_disabled);
atomic_inc(&cpu_buffer->resize_disabled);
bpage->page = rb_page_desc_page(pdesc,
cpu_buffer->meta_page->reader_page.id);
if (!bpage->page)
goto fail_free_reader;
/*
* The meta-page can only describe which of the ring-buffer page
* is the reader. There is no need to init the rest of the
* ring-buffer.
*/
return cpu_buffer;
}
page = alloc_pages_node(cpu_to_node(cpu), GFP_KERNEL, 0);
if (!page)
goto fail_free_reader;
bpage->page = page_address(page);
rb_init_page(bpage->page);
INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
INIT_LIST_HEAD(&cpu_buffer->new_pages);
ret = rb_allocate_pages(cpu_buffer, nr_pages);
if (ret < 0)
goto fail_free_reader;
cpu_buffer->head_page
= list_entry(cpu_buffer->pages, struct buffer_page, list);
cpu_buffer->tail_page = cpu_buffer->commit_page = cpu_buffer->head_page;
rb_head_page_activate(cpu_buffer);
return cpu_buffer;
fail_free_reader:
free_buffer_page(cpu_buffer->reader_page);
fail_free_buffer:
kfree(cpu_buffer);
return NULL;
}
static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
{
struct list_head *head = cpu_buffer->pages;
struct buffer_page *bpage, *tmp;
irq_work_sync(&cpu_buffer->irq_work.work);
if (cpu_buffer->writer)
/* the ring_buffer doesn't own the data pages */
cpu_buffer->reader_page->page = NULL;
free_buffer_page(cpu_buffer->reader_page);
if (head) {
rb_head_page_deactivate(cpu_buffer);
list_for_each_entry_safe(bpage, tmp, head, list) {
list_del_init(&bpage->list);
free_buffer_page(bpage);
}
bpage = list_entry(head, struct buffer_page, list);
free_buffer_page(bpage);
}
free_page((unsigned long)cpu_buffer->free_page);
kfree(cpu_buffer);
}
/**
* __ring_buffer_alloc - allocate a new ring_buffer
* @size: the size in bytes per cpu that is needed.
* @flags: attributes to set for the ring buffer.
* @key: ring buffer reader_lock_key.
*
* Currently the only flag that is available is the RB_FL_OVERWRITE
* flag. This flag means that the buffer will overwrite old data
* when the buffer wraps. If this flag is not set, the buffer will
* drop data when the tail hits the head.
*/
struct trace_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags,
struct lock_class_key *key,
struct ring_buffer_writer *writer)
{
struct trace_buffer *buffer;
long nr_pages;
int bsize;
int cpu;
int ret;
/* keep it in its own cache line */
buffer = kzalloc(ALIGN(sizeof(*buffer), cache_line_size()),
GFP_KERNEL);
if (!buffer)
return NULL;
if (!zalloc_cpumask_var(&buffer->cpumask, GFP_KERNEL))
goto fail_free_buffer;
nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
buffer->flags = flags;
buffer->clock = trace_clock_local;
buffer->reader_lock_key = key;
if (writer) {
buffer->writer = writer;
atomic_inc(&buffer->record_disabled);
}
init_irq_work(&buffer->irq_work.work, rb_wake_up_waiters);
init_waitqueue_head(&buffer->irq_work.waiters);
/* need at least two pages */
if (nr_pages < 2)
nr_pages = 2;
buffer->cpus = nr_cpu_ids;
bsize = sizeof(void *) * nr_cpu_ids;
buffer->buffers = kzalloc(ALIGN(bsize, cache_line_size()),
GFP_KERNEL);
if (!buffer->buffers)
goto fail_free_cpumask;
cpu = raw_smp_processor_id();
cpumask_set_cpu(cpu, buffer->cpumask);
buffer->buffers[cpu] = rb_allocate_cpu_buffer(buffer, nr_pages, cpu);
if (!buffer->buffers[cpu])
goto fail_free_buffers;
ret = cpuhp_state_add_instance(CPUHP_TRACE_RB_PREPARE, &buffer->node);
if (ret < 0)
goto fail_free_buffers;
mutex_init(&buffer->mutex);
return buffer;
fail_free_buffers:
for_each_buffer_cpu(buffer, cpu) {
if (buffer->buffers[cpu])
rb_free_cpu_buffer(buffer->buffers[cpu]);
}
kfree(buffer->buffers);
fail_free_cpumask:
free_cpumask_var(buffer->cpumask);
fail_free_buffer:
kfree(buffer);
return NULL;
}
EXPORT_SYMBOL_GPL(__ring_buffer_alloc);
/**
* ring_buffer_free - free a ring buffer.
* @buffer: the buffer to free.
*/
void
ring_buffer_free(struct trace_buffer *buffer)
{
int cpu;
cpuhp_state_remove_instance(CPUHP_TRACE_RB_PREPARE, &buffer->node);
irq_work_sync(&buffer->irq_work.work);
for_each_buffer_cpu(buffer, cpu)
rb_free_cpu_buffer(buffer->buffers[cpu]);
kfree(buffer->buffers);
free_cpumask_var(buffer->cpumask);
kfree(buffer);
}
EXPORT_SYMBOL_GPL(ring_buffer_free);
void ring_buffer_set_clock(struct trace_buffer *buffer,
u64 (*clock)(void))
{
buffer->clock = clock;
}
void ring_buffer_set_time_stamp_abs(struct trace_buffer *buffer, bool abs)
{
buffer->time_stamp_abs = abs;
}
bool ring_buffer_time_stamp_abs(struct trace_buffer *buffer)
{
return buffer->time_stamp_abs;
}
static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer);
static inline unsigned long rb_page_entries(struct buffer_page *bpage)
{
return local_read(&bpage->entries) & RB_WRITE_MASK;
}
static inline unsigned long rb_page_write(struct buffer_page *bpage)
{
return local_read(&bpage->write) & RB_WRITE_MASK;
}
static bool
rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned long nr_pages)
{
struct list_head *tail_page, *to_remove, *next_page;
struct buffer_page *to_remove_page, *tmp_iter_page;
struct buffer_page *last_page, *first_page;
unsigned long nr_removed;
unsigned long head_bit;
int page_entries;
head_bit = 0;
raw_spin_lock_irq(&cpu_buffer->reader_lock);
atomic_inc(&cpu_buffer->record_disabled);
/*
* We don't race with the readers since we have acquired the reader
* lock. We also don't race with writers after disabling recording.
* This makes it easy to figure out the first and the last page to be
* removed from the list. We unlink all the pages in between including
* the first and last pages. This is done in a busy loop so that we
* lose the least number of traces.
* The pages are freed after we restart recording and unlock readers.
*/
tail_page = &cpu_buffer->tail_page->list;
/*
* tail page might be on reader page, we remove the next page
* from the ring buffer
*/
if (cpu_buffer->tail_page == cpu_buffer->reader_page)
tail_page = rb_list_head(tail_page->next);
to_remove = tail_page;
/* start of pages to remove */
first_page = list_entry(rb_list_head(to_remove->next),
struct buffer_page, list);
for (nr_removed = 0; nr_removed < nr_pages; nr_removed++) {
to_remove = rb_list_head(to_remove)->next;
head_bit |= (unsigned long)to_remove & RB_PAGE_HEAD;
}
/* Read iterators need to reset themselves when some pages removed */
cpu_buffer->pages_removed += nr_removed;
next_page = rb_list_head(to_remove)->next;
/*
* Now we remove all pages between tail_page and next_page.
* Make sure that we have head_bit value preserved for the
* next page
*/
tail_page->next = (struct list_head *)((unsigned long)next_page |
head_bit);
next_page = rb_list_head(next_page);
next_page->prev = tail_page;
/* make sure pages points to a valid page in the ring buffer */
cpu_buffer->pages = next_page;
/* update head page */
if (head_bit)
cpu_buffer->head_page = list_entry(next_page,
struct buffer_page, list);
/* pages are removed, resume tracing and then free the pages */
atomic_dec(&cpu_buffer->record_disabled);
raw_spin_unlock_irq(&cpu_buffer->reader_lock);
RB_WARN_ON(cpu_buffer, list_empty(cpu_buffer->pages));
/* last buffer page to remove */
last_page = list_entry(rb_list_head(to_remove), struct buffer_page,
list);
tmp_iter_page = first_page;
do {
cond_resched();
to_remove_page = tmp_iter_page;
rb_inc_page(&tmp_iter_page);
/* update the counters */
page_entries = rb_page_entries(to_remove_page);
if (page_entries) {
/*
* If something was added to this page, it was full
* since it is not the tail page. So we deduct the
* bytes consumed in ring buffer from here.
* Increment overrun to account for the lost events.
*/
local_add(page_entries, &cpu_buffer->overrun);
local_sub(rb_page_commit(to_remove_page), &cpu_buffer->entries_bytes);
local_inc(&cpu_buffer->pages_lost);
}
/*
* We have already removed references to this list item, just
* free up the buffer_page and its page
*/
free_buffer_page(to_remove_page);
nr_removed--;
} while (to_remove_page != last_page);
RB_WARN_ON(cpu_buffer, nr_removed);
return nr_removed == 0;
}
static bool
rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer)
{
struct list_head *pages = &cpu_buffer->new_pages;
unsigned long flags;
bool success;
int retries;
/* Can be called at early boot up, where interrupts must not been enabled */
raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
/*
* We are holding the reader lock, so the reader page won't be swapped
* in the ring buffer. Now we are racing with the writer trying to
* move head page and the tail page.
* We are going to adapt the reader page update process where:
* 1. We first splice the start and end of list of new pages between
* the head page and its previous page.
* 2. We cmpxchg the prev_page->next to point from head page to the
* start of new pages list.
* 3. Finally, we update the head->prev to the end of new list.
*
* We will try this process 10 times, to make sure that we don't keep
* spinning.
*/
retries = 10;
success = false;
while (retries--) {
struct list_head *head_page, *prev_page, *r;
struct list_head *last_page, *first_page;
struct list_head *head_page_with_bit;
struct buffer_page *hpage = rb_set_head_page(cpu_buffer);
if (!hpage)
break;
head_page = &hpage->list;
prev_page = head_page->prev;
first_page = pages->next;
last_page = pages->prev;
head_page_with_bit = (struct list_head *)
((unsigned long)head_page | RB_PAGE_HEAD);
last_page->next = head_page_with_bit;
first_page->prev = prev_page;
r = cmpxchg(&prev_page->next, head_page_with_bit, first_page);
if (r == head_page_with_bit) {
/*
* yay, we replaced the page pointer to our new list,
* now, we just have to update to head page's prev
* pointer to point to end of list
*/
head_page->prev = last_page;
success = true;
break;
}
}
if (success)
INIT_LIST_HEAD(pages);
/*
* If we weren't successful in adding in new pages, warn and stop
* tracing
*/
RB_WARN_ON(cpu_buffer, !success);
raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
/* free pages if they weren't inserted */
if (!success) {
struct buffer_page *bpage, *tmp;
list_for_each_entry_safe(bpage, tmp, &cpu_buffer->new_pages,
list) {
list_del_init(&bpage->list);
free_buffer_page(bpage);
}
}
return success;
}
static void rb_update_pages(struct ring_buffer_per_cpu *cpu_buffer)
{
bool success;
if (cpu_buffer->nr_pages_to_update > 0)
success = rb_insert_pages(cpu_buffer);
else
success = rb_remove_pages(cpu_buffer,
-cpu_buffer->nr_pages_to_update);
if (success)
cpu_buffer->nr_pages += cpu_buffer->nr_pages_to_update;
}
static void update_pages_handler(struct work_struct *work)
{
struct ring_buffer_per_cpu *cpu_buffer = container_of(work,
struct ring_buffer_per_cpu, update_pages_work);
rb_update_pages(cpu_buffer);
complete(&cpu_buffer->update_done);
}
/**
* ring_buffer_resize - resize the ring buffer
* @buffer: the buffer to resize.
* @size: the new size.
* @cpu_id: the cpu buffer to resize
*
* Minimum size is 2 * BUF_PAGE_SIZE.
*
* Returns 0 on success and < 0 on failure.
*/
int ring_buffer_resize(struct trace_buffer *buffer, unsigned long size,
int cpu_id)
{
struct ring_buffer_per_cpu *cpu_buffer;
unsigned long nr_pages;
int cpu, err;
/*
* Always succeed at resizing a non-existent buffer:
*/
if (!buffer)
return 0;
/* Make sure the requested buffer exists */
if (cpu_id != RING_BUFFER_ALL_CPUS &&
!cpumask_test_cpu(cpu_id, buffer->cpumask))
return 0;
nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
/* we need a minimum of two pages */
if (nr_pages < 2)
nr_pages = 2;
/* prevent another thread from changing buffer sizes */
mutex_lock(&buffer->mutex);
atomic_inc(&buffer->resizing);
if (cpu_id == RING_BUFFER_ALL_CPUS) {
/*
* Don't succeed if resizing is disabled, as a reader might be
* manipulating the ring buffer and is expecting a sane state while
* this is true.
*/
for_each_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
if (atomic_read(&cpu_buffer->resize_disabled)) {
err = -EBUSY;
goto out_err_unlock;
}
}
/* calculate the pages to update */
for_each_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
cpu_buffer->nr_pages_to_update = nr_pages -
cpu_buffer->nr_pages;
/*
* nothing more to do for removing pages or no update
*/
if (cpu_buffer->nr_pages_to_update <= 0)
continue;
/*
* to add pages, make sure all new pages can be
* allocated without receiving ENOMEM
*/
INIT_LIST_HEAD(&cpu_buffer->new_pages);
if (__rb_allocate_pages(cpu_buffer, cpu_buffer->nr_pages_to_update,
&cpu_buffer->new_pages)) {
/* not enough memory for new pages */
err = -ENOMEM;
goto out_err;
}
cond_resched();
}
cpus_read_lock();
/*
* Fire off all the required work handlers
* We can't schedule on offline CPUs, but it's not necessary
* since we can change their buffer sizes without any race.
*/
for_each_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
if (!cpu_buffer->nr_pages_to_update)
continue;
/* Can't run something on an offline CPU. */
if (!cpu_online(cpu)) {
rb_update_pages(cpu_buffer);
cpu_buffer->nr_pages_to_update = 0;
} else {
/* Run directly if possible. */
migrate_disable();
if (cpu != smp_processor_id()) {
migrate_enable();
schedule_work_on(cpu,
&cpu_buffer->update_pages_work);
} else {
update_pages_handler(&cpu_buffer->update_pages_work);
migrate_enable();
}
}
}
/* wait for all the updates to complete */
for_each_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
if (!cpu_buffer->nr_pages_to_update)
continue;
if (cpu_online(cpu))
wait_for_completion(&cpu_buffer->update_done);
cpu_buffer->nr_pages_to_update = 0;
}
cpus_read_unlock();
} else {
cpu_buffer = buffer->buffers[cpu_id];
if (nr_pages == cpu_buffer->nr_pages)
goto out;
/*
* Don't succeed if resizing is disabled, as a reader might be
* manipulating the ring buffer and is expecting a sane state while
* this is true.
*/
if (atomic_read(&cpu_buffer->resize_disabled)) {
err = -EBUSY;
goto out_err_unlock;
}
cpu_buffer->nr_pages_to_update = nr_pages -
cpu_buffer->nr_pages;
INIT_LIST_HEAD(&cpu_buffer->new_pages);
if (cpu_buffer->nr_pages_to_update > 0 &&
__rb_allocate_pages(cpu_buffer, cpu_buffer->nr_pages_to_update,
&cpu_buffer->new_pages)) {
err = -ENOMEM;
goto out_err;
}
cpus_read_lock();
/* Can't run something on an offline CPU. */
if (!cpu_online(cpu_id))
rb_update_pages(cpu_buffer);
else {
/* Run directly if possible. */
migrate_disable();
if (cpu_id == smp_processor_id()) {
rb_update_pages(cpu_buffer);
migrate_enable();
} else {
migrate_enable();
schedule_work_on(cpu_id,
&cpu_buffer->update_pages_work);
wait_for_completion(&cpu_buffer->update_done);
}
}
cpu_buffer->nr_pages_to_update = 0;
cpus_read_unlock();
}
out:
/*
* The ring buffer resize can happen with the ring buffer
* enabled, so that the update disturbs the tracing as little
* as possible. But if the buffer is disabled, we do not need
* to worry about that, and we can take the time to verify
* that the buffer is not corrupt.
*/
if (atomic_read(&buffer->record_disabled)) {
atomic_inc(&buffer->record_disabled);
/*
* Even though the buffer was disabled, we must make sure
* that it is truly disabled before calling rb_check_pages.
* There could have been a race between checking
* record_disable and incrementing it.
*/
synchronize_rcu();
for_each_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
rb_check_pages(cpu_buffer);
}
atomic_dec(&buffer->record_disabled);
}
atomic_dec(&buffer->resizing);
mutex_unlock(&buffer->mutex);
return 0;
out_err:
for_each_buffer_cpu(buffer, cpu) {
struct buffer_page *bpage, *tmp;
cpu_buffer = buffer->buffers[cpu];
cpu_buffer->nr_pages_to_update = 0;
if (list_empty(&cpu_buffer->new_pages))
continue;
list_for_each_entry_safe(bpage, tmp, &cpu_buffer->new_pages,
list) {
list_del_init(&bpage->list);
free_buffer_page(bpage);
}
}
out_err_unlock:
atomic_dec(&buffer->resizing);
mutex_unlock(&buffer->mutex);
return err;
}
EXPORT_SYMBOL_GPL(ring_buffer_resize);
void ring_buffer_change_overwrite(struct trace_buffer *buffer, int val)
{
mutex_lock(&buffer->mutex);
if (val)
buffer->flags |= RB_FL_OVERWRITE;
else
buffer->flags &= ~RB_FL_OVERWRITE;
mutex_unlock(&buffer->mutex);
}
EXPORT_SYMBOL_GPL(ring_buffer_change_overwrite);
static __always_inline void *__rb_page_index(struct buffer_page *bpage, unsigned index)
{
return bpage->page->data + index;
}
static __always_inline struct ring_buffer_event *
rb_reader_event(struct ring_buffer_per_cpu *cpu_buffer)
{
return __rb_page_index(cpu_buffer->reader_page,
cpu_buffer->reader_page->read);
}
static struct ring_buffer_event *
rb_iter_head_event(struct ring_buffer_iter *iter)
{
struct ring_buffer_event *event;
struct buffer_page *iter_head_page = iter->head_page;
unsigned long commit;
unsigned length;
if (iter->head != iter->next_event)
return iter->event;
/*
* When the writer goes across pages, it issues a cmpxchg which
* is a mb(), which will synchronize with the rmb here.
* (see rb_tail_page_update() and __rb_reserve_next())
*/
commit = rb_page_commit(iter_head_page);
smp_rmb();
/* An event needs to be at least 8 bytes in size */
if (iter->head > commit - 8)
goto reset;
event = __rb_page_index(iter_head_page, iter->head);
length = rb_event_length(event);
/*
* READ_ONCE() doesn't work on functions and we don't want the
* compiler doing any crazy optimizations with length.
*/
barrier();
if ((iter->head + length) > commit || length > BUF_PAGE_SIZE)
/* Writer corrupted the read? */
goto reset;
memcpy(iter->event, event, length);
/*
* If the page stamp is still the same after this rmb() then the
* event was safely copied without the writer entering the page.
*/
smp_rmb();
/* Make sure the page didn't change since we read this */
if (iter->page_stamp != iter_head_page->page->time_stamp ||
commit > rb_page_commit(iter_head_page))
goto reset;
iter->next_event = iter->head + length;
return iter->event;
reset:
/* Reset to the beginning */
iter->page_stamp = iter->read_stamp = iter->head_page->page->time_stamp;
iter->head = 0;
iter->next_event = 0;
iter->missed_events = 1;
return NULL;
}
/* Size is determined by what has been committed */
static __always_inline unsigned rb_page_size(struct buffer_page *bpage)
{
return rb_page_commit(bpage);
}
static __always_inline unsigned
rb_commit_index(struct ring_buffer_per_cpu *cpu_buffer)
{
return rb_page_commit(cpu_buffer->commit_page);
}
static __always_inline unsigned
rb_event_index(struct ring_buffer_event *event)
{
unsigned long addr = (unsigned long)event;
return (addr & ~PAGE_MASK) - BUF_PAGE_HDR_SIZE;
}
static void rb_inc_iter(struct ring_buffer_iter *iter)
{
struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
/*
* The iterator could be on the reader page (it starts there).
* But the head could have moved, since the reader was
* found. Check for this case and assign the iterator
* to the head page instead of next.
*/
if (iter->head_page == cpu_buffer->reader_page)
iter->head_page = rb_set_head_page(cpu_buffer);
else
rb_inc_page(&iter->head_page);
iter->page_stamp = iter->read_stamp = iter->head_page->page->time_stamp;
iter->head = 0;
iter->next_event = 0;
}
/*
* rb_handle_head_page - writer hit the head page
*
* Returns: +1 to retry page
* 0 to continue
* -1 on error
*/
static int
rb_handle_head_page(struct ring_buffer_per_cpu *cpu_buffer,
struct buffer_page *tail_page,
struct buffer_page *next_page)
{
struct buffer_page *new_head;
int entries;
int type;
int ret;
entries = rb_page_entries(next_page);
/*
* The hard part is here. We need to move the head
* forward, and protect against both readers on
* other CPUs and writers coming in via interrupts.
*/
type = rb_head_page_set_update(cpu_buffer, next_page, tail_page,
RB_PAGE_HEAD);
/*
* type can be one of four:
* NORMAL - an interrupt already moved it for us
* HEAD - we are the first to get here.
* UPDATE - we are the interrupt interrupting
* a current move.
* MOVED - a reader on another CPU moved the next
* pointer to its reader page. Give up
* and try again.
*/
switch (type) {
case RB_PAGE_HEAD:
/*
* We changed the head to UPDATE, thus
* it is our responsibility to update
* the counters.
*/
local_add(entries, &cpu_buffer->overrun);
local_sub(rb_page_commit(next_page), &cpu_buffer->entries_bytes);
local_inc(&cpu_buffer->pages_lost);
if (READ_ONCE(cpu_buffer->mapped)) {
/* Ensure the meta_page is ready */
smp_rmb();
WRITE_ONCE(cpu_buffer->meta_page->overrun,
local_read(&cpu_buffer->overrun));
WRITE_ONCE(cpu_buffer->meta_page->pages_lost,
local_read(&cpu_buffer->pages_lost));
}
/*
* The entries will be zeroed out when we move the
* tail page.
*/
/* still more to do */
break;
case RB_PAGE_UPDATE:
/*
* This is an interrupt that interrupt the
* previous update. Still more to do.
*/
break;
case RB_PAGE_NORMAL:
/*
* An interrupt came in before the update
* and processed this for us.
* Nothing left to do.
*/
return 1;
case RB_PAGE_MOVED:
/*
* The reader is on another CPU and just did
* a swap with our next_page.
* Try again.
*/
return 1;
default:
RB_WARN_ON(cpu_buffer, 1); /* WTF??? */
return -1;
}
/*
* Now that we are here, the old head pointer is
* set to UPDATE. This will keep the reader from
* swapping the head page with the reader page.
* The reader (on another CPU) will spin till
* we are finished.
*
* We just need to protect against interrupts
* doing the job. We will set the next pointer
* to HEAD. After that, we set the old pointer
* to NORMAL, but only if it was HEAD before.
* otherwise we are an interrupt, and only
* want the outer most commit to reset it.
*/
new_head = next_page;
rb_inc_page(&new_head);
ret = rb_head_page_set_head(cpu_buffer, new_head, next_page,
RB_PAGE_NORMAL);
/*
* Valid returns are:
* HEAD - an interrupt came in and already set it.
* NORMAL - One of two things:
* 1) We really set it.
* 2) A bunch of interrupts came in and moved
* the page forward again.
*/
switch (ret) {
case RB_PAGE_HEAD:
case RB_PAGE_NORMAL:
/* OK */
break;
default:
RB_WARN_ON(cpu_buffer, 1);
return -1;
}
/*
* It is possible that an interrupt came in,
* set the head up, then more interrupts came in
* and moved it again. When we get back here,
* the page would have been set to NORMAL but we
* just set it back to HEAD.
*
* How do you detect this? Well, if that happened
* the tail page would have moved.
*/
if (ret == RB_PAGE_NORMAL) {
struct buffer_page *buffer_tail_page;
buffer_tail_page = READ_ONCE(cpu_buffer->tail_page);
/*
* If the tail had moved passed next, then we need
* to reset the pointer.
*/
if (buffer_tail_page != tail_page &&
buffer_tail_page != next_page)
rb_head_page_set_normal(cpu_buffer, new_head,
next_page,
RB_PAGE_HEAD);
}
/*
* If this was the outer most commit (the one that
* changed the original pointer from HEAD to UPDATE),
* then it is up to us to reset it to NORMAL.
*/
if (type == RB_PAGE_HEAD) {
ret = rb_head_page_set_normal(cpu_buffer, next_page,
tail_page,
RB_PAGE_UPDATE);
if (RB_WARN_ON(cpu_buffer,
ret != RB_PAGE_UPDATE))
return -1;
}
return 0;
}
static inline void
rb_reset_tail(struct ring_buffer_per_cpu *cpu_buffer,
unsigned long tail, struct rb_event_info *info)
{
struct buffer_page *tail_page = info->tail_page;
struct ring_buffer_event *event;
unsigned long length = info->length;
/*
* Only the event that crossed the page boundary
* must fill the old tail_page with padding.
*/
if (tail >= BUF_PAGE_SIZE) {
/*
* If the page was filled, then we still need
* to update the real_end. Reset it to zero
* and the reader will ignore it.
*/
if (tail == BUF_PAGE_SIZE)
tail_page->real_end = 0;
local_sub(length, &tail_page->write);
return;
}
event = __rb_page_index(tail_page, tail);
/*
* Save the original length to the meta data.
* This will be used by the reader to add lost event
* counter.
*/
tail_page->real_end = tail;
/*
* If this event is bigger than the minimum size, then
* we need to be careful that we don't subtract the
* write counter enough to allow another writer to slip
* in on this page.
* We put in a discarded commit instead, to make sure
* that this space is not used again, and this space will
* not be accounted into 'entries_bytes'.
*
* If we are less than the minimum size, we don't need to
* worry about it.
*/
if (tail > (BUF_PAGE_SIZE - RB_EVNT_MIN_SIZE)) {
/* No room for any events */
/* Mark the rest of the page with padding */
rb_event_set_padding(event);
/* Make sure the padding is visible before the write update */
smp_wmb();
/* Set the write back to the previous setting */
local_sub(length, &tail_page->write);
return;
}
/* Put in a discarded event */
event->array[0] = (BUF_PAGE_SIZE - tail) - RB_EVNT_HDR_SIZE;
event->type_len = RINGBUF_TYPE_PADDING;
/* time delta must be non zero */
event->time_delta = 1;
/* account for padding bytes */
local_add(BUF_PAGE_SIZE - tail, &cpu_buffer->entries_bytes);
/* Make sure the padding is visible before the tail_page->write update */
smp_wmb();
/* Set write to end of buffer */
length = (tail + length) - BUF_PAGE_SIZE;
local_sub(length, &tail_page->write);
}
static inline void rb_end_commit(struct ring_buffer_per_cpu *cpu_buffer);
/*
* This is the slow path, force gcc not to inline it.
*/
static noinline struct ring_buffer_event *
rb_move_tail(struct ring_buffer_per_cpu *cpu_buffer,
unsigned long tail, struct rb_event_info *info)
{
struct buffer_page *tail_page = info->tail_page;
struct buffer_page *commit_page = cpu_buffer->commit_page;
struct trace_buffer *buffer = cpu_buffer->buffer;
struct buffer_page *next_page;
int ret;
next_page = tail_page;
rb_inc_page(&next_page);
/*
* If for some reason, we had an interrupt storm that made
* it all the way around the buffer, bail, and warn
* about it.
*/
if (unlikely(next_page == commit_page)) {
local_inc(&cpu_buffer->commit_overrun);
goto out_reset;
}
/*
* This is where the fun begins!
*
* We are fighting against races between a reader that
* could be on another CPU trying to swap its reader
* page with the buffer head.
*
* We are also fighting against interrupts coming in and
* moving the head or tail on us as well.
*
* If the next page is the head page then we have filled
* the buffer, unless the commit page is still on the
* reader page.
*/
if (rb_is_head_page(next_page, &tail_page->list)) {
/*
* If the commit is not on the reader page, then
* move the header page.
*/
if (!rb_is_reader_page(cpu_buffer->commit_page)) {
/*
* If we are not in overwrite mode,
* this is easy, just stop here.
*/
if (!(buffer->flags & RB_FL_OVERWRITE)) {
local_inc(&cpu_buffer->dropped_events);
goto out_reset;
}
ret = rb_handle_head_page(cpu_buffer,
tail_page,
next_page);
if (ret < 0)
goto out_reset;
if (ret)
goto out_again;
} else {
/*
* We need to be careful here too. The
* commit page could still be on the reader
* page. We could have a small buffer, and
* have filled up the buffer with events
* from interrupts and such, and wrapped.
*
* Note, if the tail page is also on the
* reader_page, we let it move out.
*/
if (unlikely((cpu_buffer->commit_page !=
cpu_buffer->tail_page) &&
(cpu_buffer->commit_page ==
cpu_buffer->reader_page))) {
local_inc(&cpu_buffer->commit_overrun);
goto out_reset;
}
}
}
rb_tail_page_update(cpu_buffer, tail_page, next_page);
out_again:
rb_reset_tail(cpu_buffer, tail, info);
/* Commit what we have for now. */
rb_end_commit(cpu_buffer);
/* rb_end_commit() decs committing */
local_inc(&cpu_buffer->committing);
/* fail and let the caller try again */
return ERR_PTR(-EAGAIN);
out_reset:
/* reset write */
rb_reset_tail(cpu_buffer, tail, info);
return NULL;
}
/* Slow path */
static struct ring_buffer_event *
rb_add_time_stamp(struct ring_buffer_event *event, u64 delta, bool abs)
{
if (abs)
event->type_len = RINGBUF_TYPE_TIME_STAMP;
else
event->type_len = RINGBUF_TYPE_TIME_EXTEND;
/* Not the first event on the page, or not delta? */
if (abs || rb_event_index(event)) {
event->time_delta = delta & TS_MASK;
event->array[0] = delta >> TS_SHIFT;
} else {
/* nope, just zero it */
event->time_delta = 0;
event->array[0] = 0;
}
return skip_time_extend(event);
}
#ifndef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
static inline bool sched_clock_stable(void)
{
return true;
}
#endif
static void
rb_check_timestamp(struct ring_buffer_per_cpu *cpu_buffer,
struct rb_event_info *info)
{
u64 write_stamp;
WARN_ONCE(1, "Delta way too big! %llu ts=%llu before=%llu after=%llu write stamp=%llu\n%s",
(unsigned long long)info->delta,
(unsigned long long)info->ts,
(unsigned long long)info->before,
(unsigned long long)info->after,
(unsigned long long)(rb_time_read(&cpu_buffer->write_stamp, &write_stamp) ? write_stamp : 0),
sched_clock_stable() ? "" :
"If you just came from a suspend/resume,\n"
"please switch to the trace global clock:\n"
" echo global > /sys/kernel/tracing/trace_clock\n"
"or add trace_clock=global to the kernel command line\n");
}
static void rb_add_timestamp(struct ring_buffer_per_cpu *cpu_buffer,
struct ring_buffer_event **event,
struct rb_event_info *info,
u64 *delta,
unsigned int *length)
{
bool abs = info->add_timestamp &
(RB_ADD_STAMP_FORCE | RB_ADD_STAMP_ABSOLUTE);
if (unlikely(info->delta > (1ULL << 59))) {
/*
* Some timers can use more than 59 bits, and when a timestamp
* is added to the buffer, it will lose those bits.
*/
if (abs && (info->ts & TS_MSB)) {
info->delta &= ABS_TS_MASK;
/* did the clock go backwards */
} else if (info->before == info->after && info->before > info->ts) {
/* not interrupted */
static int once;
/*
* This is possible with a recalibrating of the TSC.
* Do not produce a call stack, but just report it.
*/
if (!once) {
once++;
pr_warn("Ring buffer clock went backwards: %llu -> %llu\n",
info->before, info->ts);
}
} else
rb_check_timestamp(cpu_buffer, info);
if (!abs)
info->delta = 0;
}
*event = rb_add_time_stamp(*event, info->delta, abs);
*length -= RB_LEN_TIME_EXTEND;
*delta = 0;
}
/**
* rb_update_event - update event type and data
* @cpu_buffer: The per cpu buffer of the @event
* @event: the event to update
* @info: The info to update the @event with (contains length and delta)
*
* Update the type and data fields of the @event. The length
* is the actual size that is written to the ring buffer,
* and with this, we can determine what to place into the
* data field.
*/
static void
rb_update_event(struct ring_buffer_per_cpu *cpu_buffer,
struct ring_buffer_event *event,
struct rb_event_info *info)
{
unsigned length = info->length;
u64 delta = info->delta;
unsigned int nest = local_read(&cpu_buffer->committing) - 1;
if (!WARN_ON_ONCE(nest >= MAX_NEST))
cpu_buffer->event_stamp[nest] = info->ts;
/*
* If we need to add a timestamp, then we
* add it to the start of the reserved space.
*/
if (unlikely(info->add_timestamp))
rb_add_timestamp(cpu_buffer, &event, info, &delta, &length);
event->time_delta = delta;
length -= RB_EVNT_HDR_SIZE;
if (length > RB_MAX_SMALL_DATA || RB_FORCE_8BYTE_ALIGNMENT) {
event->type_len = 0;
event->array[0] = length;
} else
event->type_len = DIV_ROUND_UP(length, RB_ALIGNMENT);
}
static unsigned rb_calculate_event_length(unsigned length)
{
struct ring_buffer_event event; /* Used only for sizeof array */
/* zero length can cause confusions */
if (!length)
length++;
if (length > RB_MAX_SMALL_DATA || RB_FORCE_8BYTE_ALIGNMENT)
length += sizeof(event.array[0]);
length += RB_EVNT_HDR_SIZE;
length = ALIGN(length, RB_ARCH_ALIGNMENT);
/*
* In case the time delta is larger than the 27 bits for it
* in the header, we need to add a timestamp. If another
* event comes in when trying to discard this one to increase
* the length, then the timestamp will be added in the allocated
* space of this event. If length is bigger than the size needed
* for the TIME_EXTEND, then padding has to be used. The events
* length must be either RB_LEN_TIME_EXTEND, or greater than or equal
* to RB_LEN_TIME_EXTEND + 8, as 8 is the minimum size for padding.
* As length is a multiple of 4, we only need to worry if it
* is 12 (RB_LEN_TIME_EXTEND + 4).
*/
if (length == RB_LEN_TIME_EXTEND + RB_ALIGNMENT)
length += RB_ALIGNMENT;
return length;
}
static inline bool
rb_try_to_discard(struct ring_buffer_per_cpu *cpu_buffer,
struct ring_buffer_event *event)
{
unsigned long new_index, old_index;
struct buffer_page *bpage;
unsigned long addr;
new_index = rb_event_index(event);
old_index = new_index + rb_event_ts_length(event);
addr = (unsigned long)event;
addr &= PAGE_MASK;
bpage = READ_ONCE(cpu_buffer->tail_page);
/*
* Make sure the tail_page is still the same and
* the next write location is the end of this event
*/
if (bpage->page == (void *)addr && rb_page_write(bpage) == old_index) {
unsigned long write_mask =
local_read(&bpage->write) & ~RB_WRITE_MASK;
unsigned long event_length = rb_event_length(event);
/*
* For the before_stamp to be different than the write_stamp
* to make sure that the next event adds an absolute
* value and does not rely on the saved write stamp, which
* is now going to be bogus.
*
* By setting the before_stamp to zero, the next event
* is not going to use the write_stamp and will instead
* create an absolute timestamp. This means there's no
* reason to update the wirte_stamp!
*/
rb_time_set(&cpu_buffer->before_stamp, 0);
/*
* If an event were to come in now, it would see that the
* write_stamp and the before_stamp are different, and assume
* that this event just added itself before updating
* the write stamp. The interrupting event will fix the
* write stamp for us, and use an absolute timestamp.
*/
/*
* This is on the tail page. It is possible that
* a write could come in and move the tail page
* and write to the next page. That is fine
* because we just shorten what is on this page.
*/
old_index += write_mask;
new_index += write_mask;
/* caution: old_index gets updated on cmpxchg failure */
if (local_try_cmpxchg(&bpage->write, &old_index, new_index)) {
/* update counters */
local_sub(event_length, &cpu_buffer->entries_bytes);
return true;
}
}
/* could not discard */
return false;
}
static void rb_start_commit(struct ring_buffer_per_cpu *cpu_buffer)
{
local_inc(&cpu_buffer->committing);
local_inc(&cpu_buffer->commits);
}
static __always_inline void
rb_set_commit_to_write(struct ring_buffer_per_cpu *cpu_buffer)
{
unsigned long max_count;
/*
* We only race with interrupts and NMIs on this CPU.
* If we own the commit event, then we can commit
* all others that interrupted us, since the interruptions
* are in stack format (they finish before they come
* back to us). This allows us to do a simple loop to
* assign the commit to the tail.
*/
again:
max_count = cpu_buffer->nr_pages * 100;
while (cpu_buffer->commit_page != READ_ONCE(cpu_buffer->tail_page)) {
if (RB_WARN_ON(cpu_buffer, !(--max_count)))
return;
if (RB_WARN_ON(cpu_buffer,
rb_is_reader_page(cpu_buffer->tail_page)))
return;
/*
* No need for a memory barrier here, as the update
* of the tail_page did it for this page.
*/
local_set(&cpu_buffer->commit_page->page->commit,
rb_page_write(cpu_buffer->commit_page));
rb_inc_page(&cpu_buffer->commit_page);
/* add barrier to keep gcc from optimizing too much */
barrier();
}
while (rb_commit_index(cpu_buffer) !=
rb_page_write(cpu_buffer->commit_page)) {
/* Make sure the readers see the content of what is committed. */
smp_wmb();
local_set(&cpu_buffer->commit_page->page->commit,
rb_page_write(cpu_buffer->commit_page));
RB_WARN_ON(cpu_buffer,
local_read(&cpu_buffer->commit_page->page->commit) &
~RB_WRITE_MASK);
barrier();
}
/* again, keep gcc from optimizing */
barrier();
/*
* If an interrupt came in just after the first while loop
* and pushed the tail page forward, we will be left with
* a dangling commit that will never go forward.
*/
if (unlikely(cpu_buffer->commit_page != READ_ONCE(cpu_buffer->tail_page)))
goto again;
}
static __always_inline void rb_end_commit(struct ring_buffer_per_cpu *cpu_buffer)
{
unsigned long commits;
if (RB_WARN_ON(cpu_buffer,
!local_read(&cpu_buffer->committing)))
return;
again:
commits = local_read(&cpu_buffer->commits);
/* synchronize with interrupts */
barrier();
if (local_read(&cpu_buffer->committing) == 1)
rb_set_commit_to_write(cpu_buffer);
local_dec(&cpu_buffer->committing);
/* synchronize with interrupts */
barrier();
/*
* Need to account for interrupts coming in between the
* updating of the commit page and the clearing of the
* committing counter.
*/
if (unlikely(local_read(&cpu_buffer->commits) != commits) &&
!local_read(&cpu_buffer->committing)) {
local_inc(&cpu_buffer->committing);
goto again;
}
}
static inline void rb_event_discard(struct ring_buffer_event *event)
{
if (extended_time(event))
event = skip_time_extend(event);
/* array[0] holds the actual length for the discarded event */
event->array[0] = rb_event_data_length(event) - RB_EVNT_HDR_SIZE;
event->type_len = RINGBUF_TYPE_PADDING;
/* time delta must be non zero */
if (!event->time_delta)
event->time_delta = 1;
}
static void rb_commit(struct ring_buffer_per_cpu *cpu_buffer)
{
local_inc(&cpu_buffer->entries);
if (READ_ONCE(cpu_buffer->mapped)) {
/* Ensure the meta_page is ready */
smp_rmb();
WRITE_ONCE(cpu_buffer->meta_page->entries,
local_read(&cpu_buffer->entries));
}
rb_end_commit(cpu_buffer);
}
static __always_inline void
rb_wakeups(struct trace_buffer *buffer, struct ring_buffer_per_cpu *cpu_buffer)
{
if (buffer->irq_work.waiters_pending) {
buffer->irq_work.waiters_pending = false;
/* irq_work_queue() supplies it's own memory barriers */
irq_work_queue(&buffer->irq_work.work);
}
if (cpu_buffer->irq_work.waiters_pending) {
cpu_buffer->irq_work.waiters_pending = false;
/* irq_work_queue() supplies it's own memory barriers */
irq_work_queue(&cpu_buffer->irq_work.work);
}
if (cpu_buffer->last_pages_touch == local_read(&cpu_buffer->pages_touched))
return;
if (cpu_buffer->reader_page == cpu_buffer->commit_page)
return;
if (!cpu_buffer->irq_work.full_waiters_pending)
return;
cpu_buffer->last_pages_touch = local_read(&cpu_buffer->pages_touched);
if (!full_hit(buffer, cpu_buffer->cpu, cpu_buffer->shortest_full))
return;
cpu_buffer->irq_work.wakeup_full = true;
cpu_buffer->irq_work.full_waiters_pending = false;
/* irq_work_queue() supplies it's own memory barriers */
irq_work_queue(&cpu_buffer->irq_work.work);
}
#ifdef CONFIG_RING_BUFFER_RECORD_RECURSION
# define do_ring_buffer_record_recursion() \
do_ftrace_record_recursion(_THIS_IP_, _RET_IP_)
#else
# define do_ring_buffer_record_recursion() do { } while (0)
#endif
/*
* The lock and unlock are done within a preempt disable section.
* The current_context per_cpu variable can only be modified
* by the current task between lock and unlock. But it can
* be modified more than once via an interrupt. To pass this
* information from the lock to the unlock without having to
* access the 'in_interrupt()' functions again (which do show
* a bit of overhead in something as critical as function tracing,
* we use a bitmask trick.
*
* bit 1 = NMI context
* bit 2 = IRQ context
* bit 3 = SoftIRQ context
* bit 4 = normal context.
*
* This works because this is the order of contexts that can
* preempt other contexts. A SoftIRQ never preempts an IRQ
* context.
*
* When the context is determined, the corresponding bit is
* checked and set (if it was set, then a recursion of that context
* happened).
*
* On unlock, we need to clear this bit. To do so, just subtract
* 1 from the current_context and AND it to itself.
*
* (binary)
* 101 - 1 = 100
* 101 & 100 = 100 (clearing bit zero)
*
* 1010 - 1 = 1001
* 1010 & 1001 = 1000 (clearing bit 1)
*
* The least significant bit can be cleared this way, and it
* just so happens that it is the same bit corresponding to
* the current context.
*
* Now the TRANSITION bit breaks the above slightly. The TRANSITION bit
* is set when a recursion is detected at the current context, and if
* the TRANSITION bit is already set, it will fail the recursion.
* This is needed because there's a lag between the changing of
* interrupt context and updating the preempt count. In this case,
* a false positive will be found. To handle this, one extra recursion
* is allowed, and this is done by the TRANSITION bit. If the TRANSITION
* bit is already set, then it is considered a recursion and the function
* ends. Otherwise, the TRANSITION bit is set, and that bit is returned.
*
* On the trace_recursive_unlock(), the TRANSITION bit will be the first
* to be cleared. Even if it wasn't the context that set it. That is,
* if an interrupt comes in while NORMAL bit is set and the ring buffer
* is called before preempt_count() is updated, since the check will
* be on the NORMAL bit, the TRANSITION bit will then be set. If an
* NMI then comes in, it will set the NMI bit, but when the NMI code
* does the trace_recursive_unlock() it will clear the TRANSITION bit
* and leave the NMI bit set. But this is fine, because the interrupt
* code that set the TRANSITION bit will then clear the NMI bit when it
* calls trace_recursive_unlock(). If another NMI comes in, it will
* set the TRANSITION bit and continue.
*
* Note: The TRANSITION bit only handles a single transition between context.
*/
static __always_inline bool
trace_recursive_lock(struct ring_buffer_per_cpu *cpu_buffer)
{
unsigned int val = cpu_buffer->current_context;
int bit = interrupt_context_level();
bit = RB_CTX_NORMAL - bit;
if (unlikely(val & (1 << (bit + cpu_buffer->nest)))) {
/*
* It is possible that this was called by transitioning
* between interrupt context, and preempt_count() has not
* been updated yet. In this case, use the TRANSITION bit.
*/
bit = RB_CTX_TRANSITION;
if (val & (1 << (bit + cpu_buffer->nest))) {
do_ring_buffer_record_recursion();
return true;
}
}
val |= (1 << (bit + cpu_buffer->nest));
cpu_buffer->current_context = val;
return false;
}
static __always_inline void
trace_recursive_unlock(struct ring_buffer_per_cpu *cpu_buffer)
{
cpu_buffer->current_context &=
cpu_buffer->current_context - (1 << cpu_buffer->nest);
}
/* The recursive locking above uses 5 bits */
#define NESTED_BITS 5
/**
* ring_buffer_nest_start - Allow to trace while nested
* @buffer: The ring buffer to modify
*
* The ring buffer has a safety mechanism to prevent recursion.
* But there may be a case where a trace needs to be done while
* tracing something else. In this case, calling this function
* will allow this function to nest within a currently active
* ring_buffer_lock_reserve().
*
* Call this function before calling another ring_buffer_lock_reserve() and
* call ring_buffer_nest_end() after the nested ring_buffer_unlock_commit().
*/
void ring_buffer_nest_start(struct trace_buffer *buffer)
{
struct ring_buffer_per_cpu *cpu_buffer;
int cpu;
/* Enabled by ring_buffer_nest_end() */
preempt_disable_notrace();
cpu = raw_smp_processor_id();
cpu_buffer = buffer->buffers[cpu];
/* This is the shift value for the above recursive locking */
cpu_buffer->nest += NESTED_BITS;
}
/**
* ring_buffer_nest_end - Allow to trace while nested
* @buffer: The ring buffer to modify
*
* Must be called after ring_buffer_nest_start() and after the
* ring_buffer_unlock_commit().
*/
void ring_buffer_nest_end(struct trace_buffer *buffer)
{
struct ring_buffer_per_cpu *cpu_buffer;
int cpu;
/* disabled by ring_buffer_nest_start() */
cpu = raw_smp_processor_id();
cpu_buffer = buffer->buffers[cpu];
/* This is the shift value for the above recursive locking */
cpu_buffer->nest -= NESTED_BITS;
preempt_enable_notrace();
}
/**
* ring_buffer_unlock_commit - commit a reserved
* @buffer: The buffer to commit to
*
* This commits the data to the ring buffer, and releases any locks held.
*
* Must be paired with ring_buffer_lock_reserve.
*/
int ring_buffer_unlock_commit(struct trace_buffer *buffer)
{
struct ring_buffer_per_cpu *cpu_buffer;
int cpu = raw_smp_processor_id();
cpu_buffer = buffer->buffers[cpu];
rb_commit(cpu_buffer);
rb_wakeups(buffer, cpu_buffer);
trace_recursive_unlock(cpu_buffer);
preempt_enable_notrace();
return 0;
}
EXPORT_SYMBOL_GPL(ring_buffer_unlock_commit);
/* Special value to validate all deltas on a page. */
#define CHECK_FULL_PAGE 1L
#ifdef CONFIG_RING_BUFFER_VALIDATE_TIME_DELTAS
static void dump_buffer_page(struct buffer_data_page *bpage,
struct rb_event_info *info,
unsigned long tail)
{
struct ring_buffer_event *event;
u64 ts, delta;
int e;
ts = bpage->time_stamp;
pr_warn(" [%lld] PAGE TIME STAMP\n", ts);
for (e = 0; e < tail; e += rb_event_length(event)) {
event = (struct ring_buffer_event *)(bpage->data + e);
switch (event->type_len) {
case RINGBUF_TYPE_TIME_EXTEND:
delta = rb_event_time_stamp(event);
ts += delta;
pr_warn(" [%lld] delta:%lld TIME EXTEND\n", ts, delta);
break;
case RINGBUF_TYPE_TIME_STAMP:
delta = rb_event_time_stamp(event);
ts = rb_fix_abs_ts(delta, ts);
pr_warn(" [%lld] absolute:%lld TIME STAMP\n", ts, delta);
break;
case RINGBUF_TYPE_PADDING:
ts += event->time_delta;
pr_warn(" [%lld] delta:%d PADDING\n", ts, event->time_delta);
break;
case RINGBUF_TYPE_DATA:
ts += event->time_delta;
pr_warn(" [%lld] delta:%d\n", ts, event->time_delta);
break;
default:
break;
}
}
}
static DEFINE_PER_CPU(atomic_t, checking);
static atomic_t ts_dump;
/*
* Check if the current event time stamp matches the deltas on
* the buffer page.
*/
static void check_buffer(struct ring_buffer_per_cpu *cpu_buffer,
struct rb_event_info *info,
unsigned long tail)
{
struct ring_buffer_event *event;
struct buffer_data_page *bpage;
u64 ts, delta;
bool full = false;
int e;
bpage = info->tail_page->page;
if (tail == CHECK_FULL_PAGE) {
full = true;
tail = local_read(&bpage->commit);
} else if (info->add_timestamp &
(RB_ADD_STAMP_FORCE | RB_ADD_STAMP_ABSOLUTE)) {
/* Ignore events with absolute time stamps */
return;
}
/*
* Do not check the first event (skip possible extends too).
* Also do not check if previous events have not been committed.
*/
if (tail <= 8 || tail > local_read(&bpage->commit))
return;
/*
* If this interrupted another event,
*/
if (atomic_inc_return(this_cpu_ptr(&checking)) != 1)
goto out;
ts = bpage->time_stamp;
for (e = 0; e < tail; e += rb_event_length(event)) {
event = (struct ring_buffer_event *)(bpage->data + e);
switch (event->type_len) {
case RINGBUF_TYPE_TIME_EXTEND:
delta = rb_event_time_stamp(event);
ts += delta;
break;
case RINGBUF_TYPE_TIME_STAMP:
delta = rb_event_time_stamp(event);
ts = rb_fix_abs_ts(delta, ts);
break;
case RINGBUF_TYPE_PADDING:
if (event->time_delta == 1)
break;
fallthrough;
case RINGBUF_TYPE_DATA:
ts += event->time_delta;
break;
default:
RB_WARN_ON(cpu_buffer, 1);
}
}
if ((full && ts > info->ts) ||
(!full && ts + info->delta != info->ts)) {
/* If another report is happening, ignore this one */
if (atomic_inc_return(&ts_dump) != 1) {
atomic_dec(&ts_dump);
goto out;
}
atomic_inc(&cpu_buffer->record_disabled);
/* There's some cases in boot up that this can happen */
WARN_ON_ONCE(system_state != SYSTEM_BOOTING);
pr_warn("[CPU: %d]TIME DOES NOT MATCH expected:%lld actual:%lld delta:%lld before:%lld after:%lld%s\n",
cpu_buffer->cpu,
ts + info->delta, info->ts, info->delta,
info->before, info->after,
full ? " (full)" : "");
dump_buffer_page(bpage, info, tail);
atomic_dec(&ts_dump);
/* Do not re-enable checking */
return;
}
out:
atomic_dec(this_cpu_ptr(&checking));
}
#else
static inline void check_buffer(struct ring_buffer_per_cpu *cpu_buffer,
struct rb_event_info *info,
unsigned long tail)
{
}
#endif /* CONFIG_RING_BUFFER_VALIDATE_TIME_DELTAS */
static struct ring_buffer_event *
__rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
struct rb_event_info *info)
{
struct ring_buffer_event *event;
struct buffer_page *tail_page;
unsigned long tail, write, w;
bool a_ok;
bool b_ok;
/* Don't let the compiler play games with cpu_buffer->tail_page */
tail_page = info->tail_page = READ_ONCE(cpu_buffer->tail_page);
/*A*/ w = local_read(&tail_page->write) & RB_WRITE_MASK;
barrier();
b_ok = rb_time_read(&cpu_buffer->before_stamp, &info->before);
a_ok = rb_time_read(&cpu_buffer->write_stamp, &info->after);
barrier();
info->ts = rb_time_stamp(cpu_buffer->buffer);
if ((info->add_timestamp & RB_ADD_STAMP_ABSOLUTE)) {
info->delta = info->ts;
} else {
/*
* If interrupting an event time update, we may need an
* absolute timestamp.
* Don't bother if this is the start of a new page (w == 0).
*/
if (!w) {
/* Use the sub-buffer timestamp */
info->delta = 0;
} else if (unlikely(!a_ok || !b_ok || info->before != info->after)) {
info->add_timestamp |= RB_ADD_STAMP_FORCE | RB_ADD_STAMP_EXTEND;
info->length += RB_LEN_TIME_EXTEND;
} else {
info->delta = info->ts - info->after;
if (unlikely(test_time_stamp(info->delta))) {
info->add_timestamp |= RB_ADD_STAMP_EXTEND;
info->length += RB_LEN_TIME_EXTEND;
}
}
}
/*B*/ rb_time_set(&cpu_buffer->before_stamp, info->ts);
/*C*/ write = local_add_return(info->length, &tail_page->write);
/* set write to only the index of the write */
write &= RB_WRITE_MASK;
tail = write - info->length;
/* See if we shot pass the end of this buffer page */
if (unlikely(write > BUF_PAGE_SIZE)) {
check_buffer(cpu_buffer, info, CHECK_FULL_PAGE);
return rb_move_tail(cpu_buffer, tail, info);
}
if (likely(tail == w)) {
/* Nothing interrupted us between A and C */
/*D*/ rb_time_set(&cpu_buffer->write_stamp, info->ts);
/*
* If something came in between C and D, the write stamp
* may now not be in sync. But that's fine as the before_stamp
* will be different and then next event will just be forced
* to use an absolute timestamp.
*/
if (likely(!(info->add_timestamp &
(RB_ADD_STAMP_FORCE | RB_ADD_STAMP_ABSOLUTE))))
/* This did not interrupt any time update */
info->delta = info->ts - info->after;
else
/* Just use full timestamp for interrupting event */
info->delta = info->ts;
check_buffer(cpu_buffer, info, tail);
} else {
u64 ts;
/* SLOW PATH - Interrupted between A and C */
/* Save the old before_stamp */
a_ok = rb_time_read(&cpu_buffer->before_stamp, &info->before);
RB_WARN_ON(cpu_buffer, !a_ok);
/*
* Read a new timestamp and update the before_stamp to make
* the next event after this one force using an absolute
* timestamp. This is in case an interrupt were to come in
* between E and F.
*/
ts = rb_time_stamp(cpu_buffer->buffer);
rb_time_set(&cpu_buffer->before_stamp, ts);
barrier();
/*E*/ a_ok = rb_time_read(&cpu_buffer->write_stamp, &info->after);
/* Was interrupted before here, write_stamp must be valid */
RB_WARN_ON(cpu_buffer, !a_ok);
barrier();
/*F*/ if (write == (local_read(&tail_page->write) & RB_WRITE_MASK) &&
info->after == info->before && info->after < ts) {
/*
* Nothing came after this event between C and F, it is
* safe to use info->after for the delta as it
* matched info->before and is still valid.
*/
info->delta = ts - info->after;
} else {
/*
* Interrupted between C and F:
* Lost the previous events time stamp. Just set the
* delta to zero, and this will be the same time as
* the event this event interrupted. And the events that
* came after this will still be correct (as they would
* have built their delta on the previous event.
*/
info->delta = 0;
}
info->ts = ts;
info->add_timestamp &= ~RB_ADD_STAMP_FORCE;
}
/*
* If this is the first commit on the page, then it has the same
* timestamp as the page itself.
*/
if (unlikely(!tail && !(info->add_timestamp &
(RB_ADD_STAMP_FORCE | RB_ADD_STAMP_ABSOLUTE))))
info->delta = 0;
/* We reserved something on the buffer */
event = __rb_page_index(tail_page, tail);
rb_update_event(cpu_buffer, event, info);
local_inc(&tail_page->entries);
/*
* If this is the first commit on the page, then update
* its timestamp.
*/
if (unlikely(!tail))
tail_page->page->time_stamp = info->ts;
/* account for these added bytes */
local_add(info->length, &cpu_buffer->entries_bytes);
return event;
}
static __always_inline struct ring_buffer_event *
rb_reserve_next_event(struct trace_buffer *buffer,
struct ring_buffer_per_cpu *cpu_buffer,
unsigned long length)
{
struct ring_buffer_event *event;
struct rb_event_info info;
int nr_loops = 0;
int add_ts_default;
rb_start_commit(cpu_buffer);
/* The commit page can not change after this */
#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
/*
* Due to the ability to swap a cpu buffer from a buffer
* it is possible it was swapped before we committed.
* (committing stops a swap). We check for it here and
* if it happened, we have to fail the write.
*/
barrier();
if (unlikely(READ_ONCE(cpu_buffer->buffer) != buffer)) {
local_dec(&cpu_buffer->committing);
local_dec(&cpu_buffer->commits);
return NULL;
}
#endif
info.length = rb_calculate_event_length(length);
if (ring_buffer_time_stamp_abs(cpu_buffer->buffer)) {
add_ts_default = RB_ADD_STAMP_ABSOLUTE;
info.length += RB_LEN_TIME_EXTEND;
if (info.length > BUF_MAX_DATA_SIZE)
goto out_fail;
} else {
add_ts_default = RB_ADD_STAMP_NONE;
}
again:
info.add_timestamp = add_ts_default;
info.delta = 0;
/*
* We allow for interrupts to reenter here and do a trace.
* If one does, it will cause this original code to loop
* back here. Even with heavy interrupts happening, this
* should only happen a few times in a row. If this happens
* 1000 times in a row, there must be either an interrupt
* storm or we have something buggy.
* Bail!
*/
if (RB_WARN_ON(cpu_buffer, ++nr_loops > 1000))
goto out_fail;
event = __rb_reserve_next(cpu_buffer, &info);
if (unlikely(PTR_ERR(event) == -EAGAIN)) {
if (info.add_timestamp & (RB_ADD_STAMP_FORCE | RB_ADD_STAMP_EXTEND))
info.length -= RB_LEN_TIME_EXTEND;
goto again;
}
if (likely(event))
return event;
out_fail:
rb_end_commit(cpu_buffer);
return NULL;
}
/**
* ring_buffer_lock_reserve - reserve a part of the buffer
* @buffer: the ring buffer to reserve from
* @length: the length of the data to reserve (excluding event header)
*
* Returns a reserved event on the ring buffer to copy directly to.
* The user of this interface will need to get the body to write into
* and can use the ring_buffer_event_data() interface.
*
* The length is the length of the data needed, not the event length
* which also includes the event header.
*
* Must be paired with ring_buffer_unlock_commit, unless NULL is returned.
* If NULL is returned, then nothing has been allocated or locked.
*/
struct ring_buffer_event *
ring_buffer_lock_reserve(struct trace_buffer *buffer, unsigned long length)
{
struct ring_buffer_per_cpu *cpu_buffer;
struct ring_buffer_event *event;
int cpu;
/* If we are tracing schedule, we don't want to recurse */
preempt_disable_notrace();
if (unlikely(atomic_read(&buffer->record_disabled)))
goto out;
cpu = raw_smp_processor_id();
if (unlikely(!cpumask_test_cpu(cpu, buffer->cpumask)))
goto out;
cpu_buffer = buffer->buffers[cpu];
if (unlikely(atomic_read(&cpu_buffer->record_disabled)))
goto out;
if (unlikely(length > BUF_MAX_DATA_SIZE))
goto out;
if (unlikely(trace_recursive_lock(cpu_buffer)))
goto out;
event = rb_reserve_next_event(buffer, cpu_buffer, length);
if (!event)
goto out_unlock;
return event;
out_unlock:
trace_recursive_unlock(cpu_buffer);
out:
preempt_enable_notrace();
return NULL;
}
EXPORT_SYMBOL_GPL(ring_buffer_lock_reserve);
/*
* Decrement the entries to the page that an event is on.
* The event does not even need to exist, only the pointer
* to the page it is on. This may only be called before the commit
* takes place.
*/
static inline void
rb_decrement_entry(struct ring_buffer_per_cpu *cpu_buffer,
struct ring_buffer_event *event)
{
unsigned long addr = (unsigned long)event;
struct buffer_page *bpage = cpu_buffer->commit_page;
struct buffer_page *start;
addr &= PAGE_MASK;
/* Do the likely case first */
if (likely(bpage->page == (void *)addr)) {
local_dec(&bpage->entries);
return;
}
/*
* Because the commit page may be on the reader page we
* start with the next page and check the end loop there.
*/
rb_inc_page(&bpage);
start = bpage;
do {
if (bpage->page == (void *)addr) {
local_dec(&bpage->entries);
return;
}
rb_inc_page(&bpage);
} while (bpage != start);
/* commit not part of this buffer?? */
RB_WARN_ON(cpu_buffer, 1);
}
/**
* ring_buffer_discard_commit - discard an event that has not been committed
* @buffer: the ring buffer
* @event: non committed event to discard
*
* Sometimes an event that is in the ring buffer needs to be ignored.
* This function lets the user discard an event in the ring buffer
* and then that event will not be read later.
*
* This function only works if it is called before the item has been
* committed. It will try to free the event from the ring buffer
* if another event has not been added behind it.
*
* If another event has been added behind it, it will set the event
* up as discarded, and perform the commit.
*
* If this function is called, do not call ring_buffer_unlock_commit on
* the event.
*/
void ring_buffer_discard_commit(struct trace_buffer *buffer,
struct ring_buffer_event *event)
{
struct ring_buffer_per_cpu *cpu_buffer;
int cpu;
/* The event is discarded regardless */
rb_event_discard(event);
cpu = smp_processor_id();
cpu_buffer = buffer->buffers[cpu];
/*
* This must only be called if the event has not been
* committed yet. Thus we can assume that preemption
* is still disabled.
*/
RB_WARN_ON(buffer, !local_read(&cpu_buffer->committing));
rb_decrement_entry(cpu_buffer, event);
if (rb_try_to_discard(cpu_buffer, event))
goto out;
out:
rb_end_commit(cpu_buffer);
trace_recursive_unlock(cpu_buffer);
preempt_enable_notrace();
}
EXPORT_SYMBOL_GPL(ring_buffer_discard_commit);
/**
* ring_buffer_write - write data to the buffer without reserving
* @buffer: The ring buffer to write to.
* @length: The length of the data being written (excluding the event header)
* @data: The data to write to the buffer.
*
* This is like ring_buffer_lock_reserve and ring_buffer_unlock_commit as
* one function. If you already have the data to write to the buffer, it
* may be easier to simply call this function.
*
* Note, like ring_buffer_lock_reserve, the length is the length of the data
* and not the length of the event which would hold the header.
*/
int ring_buffer_write(struct trace_buffer *buffer,
unsigned long length,
void *data)
{
struct ring_buffer_per_cpu *cpu_buffer;
struct ring_buffer_event *event;
void *body;
int ret = -EBUSY;
int cpu;
preempt_disable_notrace();
if (atomic_read(&buffer->record_disabled))
goto out;
cpu = raw_smp_processor_id();
if (!cpumask_test_cpu(cpu, buffer->cpumask))
goto out;
cpu_buffer = buffer->buffers[cpu];
if (atomic_read(&cpu_buffer->record_disabled))
goto out;
if (length > BUF_MAX_DATA_SIZE)
goto out;
if (unlikely(trace_recursive_lock(cpu_buffer)))
goto out;
event = rb_reserve_next_event(buffer, cpu_buffer, length);
if (!event)
goto out_unlock;
body = rb_event_data(event);
memcpy(body, data, length);
rb_commit(cpu_buffer);
rb_wakeups(buffer, cpu_buffer);
ret = 0;
out_unlock:
trace_recursive_unlock(cpu_buffer);
out:
preempt_enable_notrace();
return ret;
}
EXPORT_SYMBOL_GPL(ring_buffer_write);
/*
* The total entries in the ring buffer is the running counter
* of entries entered into the ring buffer, minus the sum of
* the entries read from the ring buffer and the number of
* entries that were overwritten.
*/
static inline unsigned long
rb_num_of_entries(struct ring_buffer_per_cpu *cpu_buffer)
{
return local_read(&cpu_buffer->entries) -
(local_read(&cpu_buffer->overrun) + cpu_buffer->read);
}
static bool rb_per_cpu_empty(struct ring_buffer_per_cpu *cpu_buffer)
{
return !rb_num_of_entries(cpu_buffer);
}
/**
* ring_buffer_record_disable - stop all writes into the buffer
* @buffer: The ring buffer to stop writes to.
*
* This prevents all writes to the buffer. Any attempt to write
* to the buffer after this will fail and return NULL.
*
* The caller should call synchronize_rcu() after this.
*/
void ring_buffer_record_disable(struct trace_buffer *buffer)
{
atomic_inc(&buffer->record_disabled);
}
EXPORT_SYMBOL_GPL(ring_buffer_record_disable);
/**
* ring_buffer_record_enable - enable writes to the buffer
* @buffer: The ring buffer to enable writes
*
* Note, multiple disables will need the same number of enables
* to truly enable the writing (much like preempt_disable).
*/
void ring_buffer_record_enable(struct trace_buffer *buffer)
{
atomic_dec(&buffer->record_disabled);
}
EXPORT_SYMBOL_GPL(ring_buffer_record_enable);
/**
* ring_buffer_record_off - stop all writes into the buffer
* @buffer: The ring buffer to stop writes to.
*
* This prevents all writes to the buffer. Any attempt to write
* to the buffer after this will fail and return NULL.
*
* This is different than ring_buffer_record_disable() as
* it works like an on/off switch, where as the disable() version
* must be paired with a enable().
*/
void ring_buffer_record_off(struct trace_buffer *buffer)
{
unsigned int rd;
unsigned int new_rd;
rd = atomic_read(&buffer->record_disabled);
do {
new_rd = rd | RB_BUFFER_OFF;
} while (!atomic_try_cmpxchg(&buffer->record_disabled, &rd, new_rd));
}
EXPORT_SYMBOL_GPL(ring_buffer_record_off);
/**
* ring_buffer_record_on - restart writes into the buffer
* @buffer: The ring buffer to start writes to.
*
* This enables all writes to the buffer that was disabled by
* ring_buffer_record_off().
*
* This is different than ring_buffer_record_enable() as
* it works like an on/off switch, where as the enable() version
* must be paired with a disable().
*/
void ring_buffer_record_on(struct trace_buffer *buffer)
{
unsigned int rd;
unsigned int new_rd;
rd = atomic_read(&buffer->record_disabled);
do {
new_rd = rd & ~RB_BUFFER_OFF;
} while (!atomic_try_cmpxchg(&buffer->record_disabled, &rd, new_rd));
}
EXPORT_SYMBOL_GPL(ring_buffer_record_on);
/**
* ring_buffer_record_is_on - return true if the ring buffer can write
* @buffer: The ring buffer to see if write is enabled
*
* Returns true if the ring buffer is in a state that it accepts writes.
*/
bool ring_buffer_record_is_on(struct trace_buffer *buffer)
{
return !atomic_read(&buffer->record_disabled);
}
/**
* ring_buffer_record_is_set_on - return true if the ring buffer is set writable
* @buffer: The ring buffer to see if write is set enabled
*
* Returns true if the ring buffer is set writable by ring_buffer_record_on().
* Note that this does NOT mean it is in a writable state.
*
* It may return true when the ring buffer has been disabled by
* ring_buffer_record_disable(), as that is a temporary disabling of
* the ring buffer.
*/
bool ring_buffer_record_is_set_on(struct trace_buffer *buffer)
{
return !(atomic_read(&buffer->record_disabled) & RB_BUFFER_OFF);
}
/**
* ring_buffer_record_disable_cpu - stop all writes into the cpu_buffer
* @buffer: The ring buffer to stop writes to.
* @cpu: The CPU buffer to stop
*
* This prevents all writes to the buffer. Any attempt to write
* to the buffer after this will fail and return NULL.
*
* The caller should call synchronize_rcu() after this.
*/
void ring_buffer_record_disable_cpu(struct trace_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return;
cpu_buffer = buffer->buffers[cpu];
atomic_inc(&cpu_buffer->record_disabled);
}
EXPORT_SYMBOL_GPL(ring_buffer_record_disable_cpu);
/**
* ring_buffer_record_enable_cpu - enable writes to the buffer
* @buffer: The ring buffer to enable writes
* @cpu: The CPU to enable.
*
* Note, multiple disables will need the same number of enables
* to truly enable the writing (much like preempt_disable).
*/
void ring_buffer_record_enable_cpu(struct trace_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return;
cpu_buffer = buffer->buffers[cpu];
atomic_dec(&cpu_buffer->record_disabled);
}
EXPORT_SYMBOL_GPL(ring_buffer_record_enable_cpu);
/**
* ring_buffer_oldest_event_ts - get the oldest event timestamp from the buffer
* @buffer: The ring buffer
* @cpu: The per CPU buffer to read from.
*/
u64 ring_buffer_oldest_event_ts(struct trace_buffer *buffer, int cpu)
{
unsigned long flags;
struct ring_buffer_per_cpu *cpu_buffer;
struct buffer_page *bpage;
u64 ret = 0;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return 0;
cpu_buffer = buffer->buffers[cpu];
raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
/*
* if the tail is on reader_page, oldest time stamp is on the reader
* page
*/
if (cpu_buffer->tail_page == cpu_buffer->reader_page)
bpage = cpu_buffer->reader_page;
else
bpage = rb_set_head_page(cpu_buffer);
if (bpage)
ret = bpage->page->time_stamp;
raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
return ret;
}
EXPORT_SYMBOL_GPL(ring_buffer_oldest_event_ts);
/**
* ring_buffer_bytes_cpu - get the number of bytes unconsumed in a cpu buffer
* @buffer: The ring buffer
* @cpu: The per CPU buffer to read from.
*/
unsigned long ring_buffer_bytes_cpu(struct trace_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
unsigned long ret;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return 0;
cpu_buffer = buffer->buffers[cpu];
ret = local_read(&cpu_buffer->entries_bytes) - cpu_buffer->read_bytes;
return ret;
}
EXPORT_SYMBOL_GPL(ring_buffer_bytes_cpu);
/**
* ring_buffer_entries_cpu - get the number of entries in a cpu buffer
* @buffer: The ring buffer
* @cpu: The per CPU buffer to get the entries from.
*/
unsigned long ring_buffer_entries_cpu(struct trace_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return 0;
cpu_buffer = buffer->buffers[cpu];
return rb_num_of_entries(cpu_buffer);
}
EXPORT_SYMBOL_GPL(ring_buffer_entries_cpu);
/**
* ring_buffer_overrun_cpu - get the number of overruns caused by the ring
* buffer wrapping around (only if RB_FL_OVERWRITE is on).
* @buffer: The ring buffer
* @cpu: The per CPU buffer to get the number of overruns from
*/
unsigned long ring_buffer_overrun_cpu(struct trace_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
unsigned long ret;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return 0;
cpu_buffer = buffer->buffers[cpu];
ret = local_read(&cpu_buffer->overrun);
return ret;
}
EXPORT_SYMBOL_GPL(ring_buffer_overrun_cpu);
/**
* ring_buffer_commit_overrun_cpu - get the number of overruns caused by
* commits failing due to the buffer wrapping around while there are uncommitted
* events, such as during an interrupt storm.
* @buffer: The ring buffer
* @cpu: The per CPU buffer to get the number of overruns from
*/
unsigned long
ring_buffer_commit_overrun_cpu(struct trace_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
unsigned long ret;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return 0;
cpu_buffer = buffer->buffers[cpu];
ret = local_read(&cpu_buffer->commit_overrun);
return ret;
}
EXPORT_SYMBOL_GPL(ring_buffer_commit_overrun_cpu);
/**
* ring_buffer_dropped_events_cpu - get the number of dropped events caused by
* the ring buffer filling up (only if RB_FL_OVERWRITE is off).
* @buffer: The ring buffer
* @cpu: The per CPU buffer to get the number of overruns from
*/
unsigned long
ring_buffer_dropped_events_cpu(struct trace_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
unsigned long ret;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return 0;
cpu_buffer = buffer->buffers[cpu];
ret = local_read(&cpu_buffer->dropped_events);
return ret;
}
EXPORT_SYMBOL_GPL(ring_buffer_dropped_events_cpu);
/**
* ring_buffer_read_events_cpu - get the number of events successfully read
* @buffer: The ring buffer
* @cpu: The per CPU buffer to get the number of events read
*/
unsigned long
ring_buffer_read_events_cpu(struct trace_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return 0;
cpu_buffer = buffer->buffers[cpu];
return cpu_buffer->read;
}
EXPORT_SYMBOL_GPL(ring_buffer_read_events_cpu);
/**
* ring_buffer_entries - get the number of entries in a buffer
* @buffer: The ring buffer
*
* Returns the total number of entries in the ring buffer
* (all CPU entries)
*/
unsigned long ring_buffer_entries(struct trace_buffer *buffer)
{
struct ring_buffer_per_cpu *cpu_buffer;
unsigned long entries = 0;
int cpu;
/* if you care about this being correct, lock the buffer */
for_each_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
entries += rb_num_of_entries(cpu_buffer);
}
return entries;
}
EXPORT_SYMBOL_GPL(ring_buffer_entries);
/**
* ring_buffer_overruns - get the number of overruns in buffer
* @buffer: The ring buffer
*
* Returns the total number of overruns in the ring buffer
* (all CPU entries)
*/
unsigned long ring_buffer_overruns(struct trace_buffer *buffer)
{
struct ring_buffer_per_cpu *cpu_buffer;
unsigned long overruns = 0;
int cpu;
/* if you care about this being correct, lock the buffer */
for_each_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
overruns += local_read(&cpu_buffer->overrun);
}
return overruns;
}
EXPORT_SYMBOL_GPL(ring_buffer_overruns);
static void rb_iter_reset(struct ring_buffer_iter *iter)
{
struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
/* Iterator usage is expected to have record disabled */
iter->head_page = cpu_buffer->reader_page;
iter->head = cpu_buffer->reader_page->read;
iter->next_event = iter->head;
iter->cache_reader_page = iter->head_page;
iter->cache_read = cpu_buffer->read;
iter->cache_pages_removed = cpu_buffer->pages_removed;
if (iter->head) {
iter->read_stamp = cpu_buffer->read_stamp;
iter->page_stamp = cpu_buffer->reader_page->page->time_stamp;
} else {
iter->read_stamp = iter->head_page->page->time_stamp;
iter->page_stamp = iter->read_stamp;
}
}
/**
* ring_buffer_iter_reset - reset an iterator
* @iter: The iterator to reset
*
* Resets the iterator, so that it will start from the beginning
* again.
*/
void ring_buffer_iter_reset(struct ring_buffer_iter *iter)
{
struct ring_buffer_per_cpu *cpu_buffer;
unsigned long flags;
if (!iter)
return;
cpu_buffer = iter->cpu_buffer;
raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
rb_iter_reset(iter);
raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
}
EXPORT_SYMBOL_GPL(ring_buffer_iter_reset);
/**
* ring_buffer_iter_empty - check if an iterator has no more to read
* @iter: The iterator to check
*/
int ring_buffer_iter_empty(struct ring_buffer_iter *iter)
{
struct ring_buffer_per_cpu *cpu_buffer;
struct buffer_page *reader;
struct buffer_page *head_page;
struct buffer_page *commit_page;
struct buffer_page *curr_commit_page;
unsigned commit;
u64 curr_commit_ts;
u64 commit_ts;
cpu_buffer = iter->cpu_buffer;
reader = cpu_buffer->reader_page;
head_page = cpu_buffer->head_page;
commit_page = cpu_buffer->commit_page;
commit_ts = commit_page->page->time_stamp;
/*
* When the writer goes across pages, it issues a cmpxchg which
* is a mb(), which will synchronize with the rmb here.
* (see rb_tail_page_update())
*/
smp_rmb();
commit = rb_page_commit(commit_page);
/* We want to make sure that the commit page doesn't change */
smp_rmb();
/* Make sure commit page didn't change */
curr_commit_page = READ_ONCE(cpu_buffer->commit_page);
curr_commit_ts = READ_ONCE(curr_commit_page->page->time_stamp);
/* If the commit page changed, then there's more data */
if (curr_commit_page != commit_page ||
curr_commit_ts != commit_ts)
return 0;
/* Still racy, as it may return a false positive, but that's OK */
return ((iter->head_page == commit_page && iter->head >= commit) ||
(iter->head_page == reader && commit_page == head_page &&
head_page->read == commit &&
iter->head == rb_page_commit(cpu_buffer->reader_page)));
}
EXPORT_SYMBOL_GPL(ring_buffer_iter_empty);
static void
rb_update_read_stamp(struct ring_buffer_per_cpu *cpu_buffer,
struct ring_buffer_event *event)
{
u64 delta;
switch (event->type_len) {
case RINGBUF_TYPE_PADDING:
return;
case RINGBUF_TYPE_TIME_EXTEND:
delta = rb_event_time_stamp(event);
cpu_buffer->read_stamp += delta;
return;
case RINGBUF_TYPE_TIME_STAMP:
delta = rb_event_time_stamp(event);
delta = rb_fix_abs_ts(delta, cpu_buffer->read_stamp);
cpu_buffer->read_stamp = delta;
return;
case RINGBUF_TYPE_DATA:
cpu_buffer->read_stamp += event->time_delta;
return;
default:
RB_WARN_ON(cpu_buffer, 1);
}
}
static void
rb_update_iter_read_stamp(struct ring_buffer_iter *iter,
struct ring_buffer_event *event)
{
u64 delta;
switch (event->type_len) {
case RINGBUF_TYPE_PADDING:
return;
case RINGBUF_TYPE_TIME_EXTEND:
delta = rb_event_time_stamp(event);
iter->read_stamp += delta;
return;
case RINGBUF_TYPE_TIME_STAMP:
delta = rb_event_time_stamp(event);
delta = rb_fix_abs_ts(delta, iter->read_stamp);
iter->read_stamp = delta;
return;
case RINGBUF_TYPE_DATA:
iter->read_stamp += event->time_delta;
return;
default:
RB_WARN_ON(iter->cpu_buffer, 1);
}
}
static bool rb_read_writer_meta_page(struct ring_buffer_per_cpu *cpu_buffer)
{
local_set(&cpu_buffer->entries, READ_ONCE(cpu_buffer->meta_page->entries));
local_set(&cpu_buffer->overrun, READ_ONCE(cpu_buffer->meta_page->overrun));
local_set(&cpu_buffer->pages_touched, READ_ONCE(cpu_buffer->meta_page->pages_touched));
local_set(&cpu_buffer->pages_lost, READ_ONCE(cpu_buffer->meta_page->pages_lost));
/*
* No need to get the "read" field, it can be tracked here as any
* reader will have to go through a rign_buffer_per_cpu.
*/
return rb_num_of_entries(cpu_buffer);
}
static struct buffer_page *
__rb_get_reader_page_from_writer(struct ring_buffer_per_cpu *cpu_buffer)
{
u32 prev_reader;
if (!rb_read_writer_meta_page(cpu_buffer))
return NULL;
/* More to read on the reader page */
if (cpu_buffer->reader_page->read < rb_page_size(cpu_buffer->reader_page))
return cpu_buffer->reader_page;
prev_reader = cpu_buffer->meta_page->reader_page.id;
WARN_ON(cpu_buffer->writer->get_reader_page(cpu_buffer->cpu));
/* nr_pages doesn't include the reader page */
if (cpu_buffer->meta_page->reader_page.id > cpu_buffer->nr_pages) {
WARN_ON(1);
return NULL;
}
cpu_buffer->reader_page->page =
(void *)cpu_buffer->page_ids[cpu_buffer->meta_page->reader_page.id];
cpu_buffer->reader_page->read = 0;
cpu_buffer->read_stamp = cpu_buffer->reader_page->page->time_stamp;
cpu_buffer->lost_events = cpu_buffer->meta_page->reader_page.lost_events;
WARN_ON(prev_reader == cpu_buffer->meta_page->reader_page.id);
return cpu_buffer->reader_page;
}
static struct buffer_page *
__rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
{
struct buffer_page *reader = NULL;
unsigned long overwrite;
unsigned long flags;
int nr_loops = 0;
bool ret;
local_irq_save(flags);
arch_spin_lock(&cpu_buffer->lock);
again:
/*
* This should normally only loop twice. But because the
* start of the reader inserts an empty page, it causes
* a case where we will loop three times. There should be no
* reason to loop four times (that I know of).
*/
if (RB_WARN_ON(cpu_buffer, ++nr_loops > 3)) {
reader = NULL;
goto out;
}
reader = cpu_buffer->reader_page;
/* If there's more to read, return this page */
if (cpu_buffer->reader_page->read < rb_page_size(reader))
goto out;
/* Never should we have an index greater than the size */
if (RB_WARN_ON(cpu_buffer,
cpu_buffer->reader_page->read > rb_page_size(reader)))
goto out;
/* check if we caught up to the tail */
reader = NULL;
if (cpu_buffer->commit_page == cpu_buffer->reader_page)
goto out;
/* Don't bother swapping if the ring buffer is empty */
if (rb_num_of_entries(cpu_buffer) == 0)
goto out;
/*
* Reset the reader page to size zero.
*/
local_set(&cpu_buffer->reader_page->write, 0);
local_set(&cpu_buffer->reader_page->entries, 0);
local_set(&cpu_buffer->reader_page->page->commit, 0);
cpu_buffer->reader_page->real_end = 0;
spin:
/*
* Splice the empty reader page into the list around the head.
*/
reader = rb_set_head_page(cpu_buffer);
if (!reader)
goto out;
cpu_buffer->reader_page->list.next = rb_list_head(reader->list.next);
cpu_buffer->reader_page->list.prev = reader->list.prev;
/*
* cpu_buffer->pages just needs to point to the buffer, it
* has no specific buffer page to point to. Lets move it out
* of our way so we don't accidentally swap it.
*/
cpu_buffer->pages = reader->list.prev;
/* The reader page will be pointing to the new head */
rb_set_list_to_head(&cpu_buffer->reader_page->list);
/*
* We want to make sure we read the overruns after we set up our
* pointers to the next object. The writer side does a
* cmpxchg to cross pages which acts as the mb on the writer
* side. Note, the reader will constantly fail the swap
* while the writer is updating the pointers, so this
* guarantees that the overwrite recorded here is the one we
* want to compare with the last_overrun.
*/
smp_mb();
overwrite = local_read(&(cpu_buffer->overrun));
/*
* Here's the tricky part.
*
* We need to move the pointer past the header page.
* But we can only do that if a writer is not currently
* moving it. The page before the header page has the
* flag bit '1' set if it is pointing to the page we want.
* but if the writer is in the process of moving it
* than it will be '2' or already moved '0'.
*/
ret = rb_head_page_replace(reader, cpu_buffer->reader_page);
/*
* If we did not convert it, then we must try again.
*/
if (!ret)
goto spin;
/*
* Yay! We succeeded in replacing the page.
*
* Now make the new head point back to the reader page.
*/
rb_list_head(reader->list.next)->prev = &cpu_buffer->reader_page->list;
rb_inc_page(&cpu_buffer->head_page);
local_inc(&cpu_buffer->pages_read);
/* Finally update the reader page to the new head */
cpu_buffer->reader_page = reader;
cpu_buffer->reader_page->read = 0;
if (overwrite != cpu_buffer->last_overrun) {
cpu_buffer->lost_events = overwrite - cpu_buffer->last_overrun;
cpu_buffer->last_overrun = overwrite;
}
if (cpu_buffer->mapped) {
WRITE_ONCE(cpu_buffer->meta_page->reader_page.read, 0);
WRITE_ONCE(cpu_buffer->meta_page->reader_page.id, reader->id);
WRITE_ONCE(cpu_buffer->meta_page->reader_page.lost_events, cpu_buffer->lost_events);
WRITE_ONCE(cpu_buffer->meta_page->pages_read, local_read(&cpu_buffer->pages_read));
}
goto again;
out:
/* Update the read_stamp on the first event */
if (reader && reader->read == 0)
cpu_buffer->read_stamp = reader->page->time_stamp;
arch_spin_unlock(&cpu_buffer->lock);
local_irq_restore(flags);
/*
* The writer has preempt disable, wait for it. But not forever
* Although, 1 second is pretty much "forever"
*/
#define USECS_WAIT 1000000
for (nr_loops = 0; nr_loops < USECS_WAIT; nr_loops++) {
/* If the write is past the end of page, a writer is still updating it */
if (likely(!reader || rb_page_write(reader) <= BUF_PAGE_SIZE))
break;
udelay(1);
/* Get the latest version of the reader write value */
smp_rmb();
}
/* The writer is not moving forward? Something is wrong */
if (RB_WARN_ON(cpu_buffer, nr_loops == USECS_WAIT))
reader = NULL;
/*
* Make sure we see any padding after the write update
* (see rb_reset_tail()).
*
* In addition, a writer may be writing on the reader page
* if the page has not been fully filled, so the read barrier
* is also needed to make sure we see the content of what is
* committed by the writer (see rb_set_commit_to_write()).
*/
smp_rmb();
return reader;
}
static struct buffer_page *
rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
{
return cpu_buffer->writer ? __rb_get_reader_page_from_writer(cpu_buffer) :
__rb_get_reader_page(cpu_buffer);
}
static void rb_advance_reader(struct ring_buffer_per_cpu *cpu_buffer)
{
struct ring_buffer_event *event;
struct buffer_page *reader;
unsigned length;
reader = rb_get_reader_page(cpu_buffer);
/* This function should not be called when buffer is empty */
if (RB_WARN_ON(cpu_buffer, !reader))
return;
event = rb_reader_event(cpu_buffer);
if (event->type_len <= RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
cpu_buffer->read++;
rb_update_read_stamp(cpu_buffer, event);
length = rb_event_length(event);
cpu_buffer->reader_page->read += length;
cpu_buffer->read_bytes += length;
if (cpu_buffer->mapped) {
WRITE_ONCE(cpu_buffer->meta_page->reader_page.read,
cpu_buffer->reader_page->read);
WRITE_ONCE(cpu_buffer->meta_page->read,
cpu_buffer->read);
}
}
static void rb_advance_iter(struct ring_buffer_iter *iter)
{
struct ring_buffer_per_cpu *cpu_buffer;
cpu_buffer = iter->cpu_buffer;
/* If head == next_event then we need to jump to the next event */
if (iter->head == iter->next_event) {
/* If the event gets overwritten again, there's nothing to do */
if (rb_iter_head_event(iter) == NULL)
return;
}
iter->head = iter->next_event;
/*
* Check if we are at the end of the buffer.
*/
if (iter->next_event >= rb_page_size(iter->head_page)) {
/* discarded commits can make the page empty */
if (iter->head_page == cpu_buffer->commit_page)
return;
rb_inc_iter(iter);
return;
}
rb_update_iter_read_stamp(iter, iter->event);
}
static int rb_lost_events(struct ring_buffer_per_cpu *cpu_buffer)
{
return cpu_buffer->lost_events;
}
static struct ring_buffer_event *
rb_buffer_peek(struct ring_buffer_per_cpu *cpu_buffer, u64 *ts,
unsigned long *lost_events)
{
struct ring_buffer_event *event;
struct buffer_page *reader;
int nr_loops = 0;
if (ts)
*ts = 0;
again:
/*
* We repeat when a time extend is encountered.
* Since the time extend is always attached to a data event,
* we should never loop more than once.
* (We never hit the following condition more than twice).
*/
if (RB_WARN_ON(cpu_buffer, ++nr_loops > 2))
return NULL;
reader = rb_get_reader_page(cpu_buffer);
if (!reader)
return NULL;
event = rb_reader_event(cpu_buffer);
switch (event->type_len) {
case RINGBUF_TYPE_PADDING:
if (rb_null_event(event))
RB_WARN_ON(cpu_buffer, 1);
/*
* Because the writer could be discarding every
* event it creates (which would probably be bad)
* if we were to go back to "again" then we may never
* catch up, and will trigger the warn on, or lock
* the box. Return the padding, and we will release
* the current locks, and try again.
*/
return event;
case RINGBUF_TYPE_TIME_EXTEND:
/* Internal data, OK to advance */
rb_advance_reader(cpu_buffer);
goto again;
case RINGBUF_TYPE_TIME_STAMP:
if (ts) {
*ts = rb_event_time_stamp(event);
*ts = rb_fix_abs_ts(*ts, reader->page->time_stamp);
ring_buffer_normalize_time_stamp(cpu_buffer->buffer,
cpu_buffer->cpu, ts);
}
/* Internal data, OK to advance */
rb_advance_reader(cpu_buffer);
goto again;
case RINGBUF_TYPE_DATA:
if (ts && !(*ts)) {
*ts = cpu_buffer->read_stamp + event->time_delta;
ring_buffer_normalize_time_stamp(cpu_buffer->buffer,
cpu_buffer->cpu, ts);
}
if (lost_events)
*lost_events = rb_lost_events(cpu_buffer);
return event;
default:
RB_WARN_ON(cpu_buffer, 1);
}
return NULL;
}
EXPORT_SYMBOL_GPL(ring_buffer_peek);
static struct ring_buffer_event *
rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
{
struct trace_buffer *buffer;
struct ring_buffer_per_cpu *cpu_buffer;
struct ring_buffer_event *event;
int nr_loops = 0;
if (ts)
*ts = 0;
cpu_buffer = iter->cpu_buffer;
buffer = cpu_buffer->buffer;
/*
* Check if someone performed a consuming read to the buffer
* or removed some pages from the buffer. In these cases,
* iterator was invalidated and we need to reset it.
*/
if (unlikely(iter->cache_read != cpu_buffer->read ||
iter->cache_reader_page != cpu_buffer->reader_page ||
iter->cache_pages_removed != cpu_buffer->pages_removed))
rb_iter_reset(iter);
again:
if (ring_buffer_iter_empty(iter))
return NULL;
/*
* As the writer can mess with what the iterator is trying
* to read, just give up if we fail to get an event after
* three tries. The iterator is not as reliable when reading
* the ring buffer with an active write as the consumer is.
* Do not warn if the three failures is reached.
*/
if (++nr_loops > 3)
return NULL;
if (rb_per_cpu_empty(cpu_buffer))
return NULL;
if (iter->head >= rb_page_size(iter->head_page)) {
rb_inc_iter(iter);
goto again;
}
event = rb_iter_head_event(iter);
if (!event)
goto again;
switch (event->type_len) {
case RINGBUF_TYPE_PADDING:
if (rb_null_event(event)) {
rb_inc_iter(iter);
goto again;
}
rb_advance_iter(iter);
return event;
case RINGBUF_TYPE_TIME_EXTEND:
/* Internal data, OK to advance */
rb_advance_iter(iter);
goto again;
case RINGBUF_TYPE_TIME_STAMP:
if (ts) {
*ts = rb_event_time_stamp(event);
*ts = rb_fix_abs_ts(*ts, iter->head_page->page->time_stamp);
ring_buffer_normalize_time_stamp(cpu_buffer->buffer,
cpu_buffer->cpu, ts);
}
/* Internal data, OK to advance */
rb_advance_iter(iter);
goto again;
case RINGBUF_TYPE_DATA:
if (ts && !(*ts)) {
*ts = iter->read_stamp + event->time_delta;
ring_buffer_normalize_time_stamp(buffer,
cpu_buffer->cpu, ts);
}
return event;
default:
RB_WARN_ON(cpu_buffer, 1);
}
return NULL;
}
EXPORT_SYMBOL_GPL(ring_buffer_iter_peek);
static inline bool rb_reader_lock(struct ring_buffer_per_cpu *cpu_buffer)
{
if (likely(!in_nmi())) {
raw_spin_lock(&cpu_buffer->reader_lock);
return true;
}
/*
* If an NMI die dumps out the content of the ring buffer
* trylock must be used to prevent a deadlock if the NMI
* preempted a task that holds the ring buffer locks. If
* we get the lock then all is fine, if not, then continue
* to do the read, but this can corrupt the ring buffer,
* so it must be permanently disabled from future writes.
* Reading from NMI is a oneshot deal.
*/
if (raw_spin_trylock(&cpu_buffer->reader_lock))
return true;
/* Continue without locking, but disable the ring buffer */
atomic_inc(&cpu_buffer->record_disabled);
return false;
}
static inline void
rb_reader_unlock(struct ring_buffer_per_cpu *cpu_buffer, bool locked)
{
if (likely(locked))
raw_spin_unlock(&cpu_buffer->reader_lock);
}
/**
* ring_buffer_peek - peek at the next event to be read
* @buffer: The ring buffer to read
* @cpu: The cpu to peak at
* @ts: The timestamp counter of this event.
* @lost_events: a variable to store if events were lost (may be NULL)
*
* This will return the event that will be read next, but does
* not consume the data.
*/
struct ring_buffer_event *
ring_buffer_peek(struct trace_buffer *buffer, int cpu, u64 *ts,
unsigned long *lost_events)
{
struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
struct ring_buffer_event *event;
unsigned long flags;
bool dolock;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return NULL;
again:
local_irq_save(flags);
dolock = rb_reader_lock(cpu_buffer);
event = rb_buffer_peek(cpu_buffer, ts, lost_events);
if (event && event->type_len == RINGBUF_TYPE_PADDING)
rb_advance_reader(cpu_buffer);
rb_reader_unlock(cpu_buffer, dolock);
local_irq_restore(flags);
if (event && event->type_len == RINGBUF_TYPE_PADDING)
goto again;
return event;
}
/** ring_buffer_iter_dropped - report if there are dropped events
* @iter: The ring buffer iterator
*
* Returns true if there was dropped events since the last peek.
*/
bool ring_buffer_iter_dropped(struct ring_buffer_iter *iter)
{
bool ret = iter->missed_events != 0;
iter->missed_events = 0;
return ret;
}
EXPORT_SYMBOL_GPL(ring_buffer_iter_dropped);
/**
* ring_buffer_iter_peek - peek at the next event to be read
* @iter: The ring buffer iterator
* @ts: The timestamp counter of this event.
*
* This will return the event that will be read next, but does
* not increment the iterator.
*/
struct ring_buffer_event *
ring_buffer_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
{
struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
struct ring_buffer_event *event;
unsigned long flags;
again:
raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
event = rb_iter_peek(iter, ts);
raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
if (event && event->type_len == RINGBUF_TYPE_PADDING)
goto again;
return event;
}
/**
* ring_buffer_consume - return an event and consume it
* @buffer: The ring buffer to get the next event from
* @cpu: the cpu to read the buffer from
* @ts: a variable to store the timestamp (may be NULL)
* @lost_events: a variable to store if events were lost (may be NULL)
*
* Returns the next event in the ring buffer, and that event is consumed.
* Meaning, that sequential reads will keep returning a different event,
* and eventually empty the ring buffer if the producer is slower.
*/
struct ring_buffer_event *
ring_buffer_consume(struct trace_buffer *buffer, int cpu, u64 *ts,
unsigned long *lost_events)
{
struct ring_buffer_per_cpu *cpu_buffer;
struct ring_buffer_event *event = NULL;
unsigned long flags;
bool dolock;
again:
/* might be called in atomic */
preempt_disable();
if (!cpumask_test_cpu(cpu, buffer->cpumask))
goto out;
cpu_buffer = buffer->buffers[cpu];
local_irq_save(flags);
dolock = rb_reader_lock(cpu_buffer);
event = rb_buffer_peek(cpu_buffer, ts, lost_events);
if (event) {
cpu_buffer->lost_events = 0;
rb_advance_reader(cpu_buffer);
}
rb_reader_unlock(cpu_buffer, dolock);
local_irq_restore(flags);
out:
preempt_enable();
if (event && event->type_len == RINGBUF_TYPE_PADDING)
goto again;
return event;
}
EXPORT_SYMBOL_GPL(ring_buffer_consume);
/**
* ring_buffer_read_prepare - Prepare for a non consuming read of the buffer
* @buffer: The ring buffer to read from
* @cpu: The cpu buffer to iterate over
* @flags: gfp flags to use for memory allocation
*
* This performs the initial preparations necessary to iterate
* through the buffer. Memory is allocated, buffer recording
* is disabled, and the iterator pointer is returned to the caller.
*
* Disabling buffer recording prevents the reading from being
* corrupted. This is not a consuming read, so a producer is not
* expected.
*
* After a sequence of ring_buffer_read_prepare calls, the user is
* expected to make at least one call to ring_buffer_read_prepare_sync.
* Afterwards, ring_buffer_read_start is invoked to get things going
* for real.
*
* This overall must be paired with ring_buffer_read_finish.
*/
struct ring_buffer_iter *
ring_buffer_read_prepare(struct trace_buffer *buffer, int cpu, gfp_t flags)
{
struct ring_buffer_per_cpu *cpu_buffer;
struct ring_buffer_iter *iter;
if (!cpumask_test_cpu(cpu, buffer->cpumask) || buffer->writer)
return NULL;
iter = kzalloc(sizeof(*iter), flags);
if (!iter)
return NULL;
/* Holds the entire event: data and meta data */
iter->event = kmalloc(BUF_PAGE_SIZE, flags);
if (!iter->event) {
kfree(iter);
return NULL;
}
cpu_buffer = buffer->buffers[cpu];
iter->cpu_buffer = cpu_buffer;
atomic_inc(&cpu_buffer->resize_disabled);
return iter;
}
EXPORT_SYMBOL_GPL(ring_buffer_read_prepare);
/**
* ring_buffer_read_prepare_sync - Synchronize a set of prepare calls
*
* All previously invoked ring_buffer_read_prepare calls to prepare
* iterators will be synchronized. Afterwards, read_buffer_read_start
* calls on those iterators are allowed.
*/
void
ring_buffer_read_prepare_sync(void)
{
synchronize_rcu();
}
EXPORT_SYMBOL_GPL(ring_buffer_read_prepare_sync);
/**
* ring_buffer_read_start - start a non consuming read of the buffer
* @iter: The iterator returned by ring_buffer_read_prepare
*
* This finalizes the startup of an iteration through the buffer.
* The iterator comes from a call to ring_buffer_read_prepare and
* an intervening ring_buffer_read_prepare_sync must have been
* performed.
*
* Must be paired with ring_buffer_read_finish.
*/
void
ring_buffer_read_start(struct ring_buffer_iter *iter)
{
struct ring_buffer_per_cpu *cpu_buffer;
unsigned long flags;
if (!iter)
return;
cpu_buffer = iter->cpu_buffer;
raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
arch_spin_lock(&cpu_buffer->lock);
rb_iter_reset(iter);
arch_spin_unlock(&cpu_buffer->lock);
raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
}
EXPORT_SYMBOL_GPL(ring_buffer_read_start);
/**
* ring_buffer_read_finish - finish reading the iterator of the buffer
* @iter: The iterator retrieved by ring_buffer_start
*
* This re-enables the recording to the buffer, and frees the
* iterator.
*/
void
ring_buffer_read_finish(struct ring_buffer_iter *iter)
{
struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
unsigned long flags;
/*
* Ring buffer is disabled from recording, here's a good place
* to check the integrity of the ring buffer.
* Must prevent readers from trying to read, as the check
* clears the HEAD page and readers require it.
*/
raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
rb_check_pages(cpu_buffer);
raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
atomic_dec(&cpu_buffer->resize_disabled);
kfree(iter->event);
kfree(iter);
}
EXPORT_SYMBOL_GPL(ring_buffer_read_finish);
/**
* ring_buffer_iter_advance - advance the iterator to the next location
* @iter: The ring buffer iterator
*
* Move the location of the iterator such that the next read will
* be the next location of the iterator.
*/
void ring_buffer_iter_advance(struct ring_buffer_iter *iter)
{
struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
unsigned long flags;
raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
rb_advance_iter(iter);
raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
}
EXPORT_SYMBOL_GPL(ring_buffer_iter_advance);
/**
* ring_buffer_size - return the size of the ring buffer (in bytes)
* @buffer: The ring buffer.
* @cpu: The CPU to get ring buffer size from.
*/
unsigned long ring_buffer_size(struct trace_buffer *buffer, int cpu)
{
/*
* Earlier, this method returned
* BUF_PAGE_SIZE * buffer->nr_pages
* Since the nr_pages field is now removed, we have converted this to
* return the per cpu buffer value.
*/
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return 0;
return BUF_PAGE_SIZE * buffer->buffers[cpu]->nr_pages;
}
EXPORT_SYMBOL_GPL(ring_buffer_size);
static void rb_clear_buffer_page(struct buffer_page *page)
{
local_set(&page->write, 0);
local_set(&page->entries, 0);
rb_init_page(page->page);
page->read = 0;
}
static void rb_reset_meta_page(struct ring_buffer_per_cpu *cpu_buffer)
{
struct ring_buffer_meta *meta = cpu_buffer->meta_page;
WRITE_ONCE(meta->entries, 0);
WRITE_ONCE(meta->overrun, 0);
WRITE_ONCE(meta->read, cpu_buffer->read);
WRITE_ONCE(meta->pages_touched, 0);
WRITE_ONCE(meta->pages_lost, 0);
WRITE_ONCE(meta->pages_read, local_read(&cpu_buffer->pages_read));
WRITE_ONCE(meta->reader_page.read, cpu_buffer->reader_page->read);
}
static void
rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
{
struct buffer_page *page;
if (cpu_buffer->writer)
return;
rb_head_page_deactivate(cpu_buffer);
cpu_buffer->head_page
= list_entry(cpu_buffer->pages, struct buffer_page, list);
rb_clear_buffer_page(cpu_buffer->head_page);
list_for_each_entry(page, cpu_buffer->pages, list) {
rb_clear_buffer_page(page);
}
cpu_buffer->tail_page = cpu_buffer->head_page;
cpu_buffer->commit_page = cpu_buffer->head_page;
INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
INIT_LIST_HEAD(&cpu_buffer->new_pages);
rb_clear_buffer_page(cpu_buffer->reader_page);
local_set(&cpu_buffer->entries_bytes, 0);
local_set(&cpu_buffer->overrun, 0);
local_set(&cpu_buffer->commit_overrun, 0);
local_set(&cpu_buffer->dropped_events, 0);
local_set(&cpu_buffer->entries, 0);
local_set(&cpu_buffer->committing, 0);
local_set(&cpu_buffer->commits, 0);
local_set(&cpu_buffer->pages_touched, 0);
local_set(&cpu_buffer->pages_lost, 0);
local_set(&cpu_buffer->pages_read, 0);
cpu_buffer->last_pages_touch = 0;
cpu_buffer->shortest_full = 0;
cpu_buffer->read = 0;
cpu_buffer->read_bytes = 0;
rb_time_set(&cpu_buffer->write_stamp, 0);
rb_time_set(&cpu_buffer->before_stamp, 0);
memset(cpu_buffer->event_stamp, 0, sizeof(cpu_buffer->event_stamp));
cpu_buffer->lost_events = 0;
cpu_buffer->last_overrun = 0;
if (cpu_buffer->mapped)
rb_reset_meta_page(cpu_buffer);
rb_head_page_activate(cpu_buffer);
cpu_buffer->pages_removed = 0;
}
/* Must have disabled the cpu buffer then done a synchronize_rcu */
static void reset_disabled_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
{
unsigned long flags;
raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
if (RB_WARN_ON(cpu_buffer, local_read(&cpu_buffer->committing)))
goto out;
arch_spin_lock(&cpu_buffer->lock);
rb_reset_cpu(cpu_buffer);
arch_spin_unlock(&cpu_buffer->lock);
out:
raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
}
/**
* ring_buffer_reset_cpu - reset a ring buffer per CPU buffer
* @buffer: The ring buffer to reset a per cpu buffer of
* @cpu: The CPU buffer to be reset
*/
void ring_buffer_reset_cpu(struct trace_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return;
/* prevent another thread from changing buffer sizes */
mutex_lock(&buffer->mutex);
atomic_inc(&cpu_buffer->resize_disabled);
atomic_inc(&cpu_buffer->record_disabled);
/* Make sure all commits have finished */
synchronize_rcu();
reset_disabled_cpu_buffer(cpu_buffer);
atomic_dec(&cpu_buffer->record_disabled);
atomic_dec(&cpu_buffer->resize_disabled);
mutex_unlock(&buffer->mutex);
}
EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);
/* Flag to ensure proper resetting of atomic variables */
#define RESET_BIT (1 << 30)
/**
* ring_buffer_reset_online_cpus - reset a ring buffer per CPU buffer
* @buffer: The ring buffer to reset a per cpu buffer of
*/
void ring_buffer_reset_online_cpus(struct trace_buffer *buffer)
{
struct ring_buffer_per_cpu *cpu_buffer;
int cpu;
/* prevent another thread from changing buffer sizes */
mutex_lock(&buffer->mutex);
for_each_online_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
atomic_add(RESET_BIT, &cpu_buffer->resize_disabled);
atomic_inc(&cpu_buffer->record_disabled);
}
/* Make sure all commits have finished */
synchronize_rcu();
for_each_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
/*
* If a CPU came online during the synchronize_rcu(), then
* ignore it.
*/
if (!(atomic_read(&cpu_buffer->resize_disabled) & RESET_BIT))
continue;
reset_disabled_cpu_buffer(cpu_buffer);
atomic_dec(&cpu_buffer->record_disabled);
atomic_sub(RESET_BIT, &cpu_buffer->resize_disabled);
}
mutex_unlock(&buffer->mutex);
}
/**
* ring_buffer_reset - reset a ring buffer
* @buffer: The ring buffer to reset all cpu buffers
*/
void ring_buffer_reset(struct trace_buffer *buffer)
{
struct ring_buffer_per_cpu *cpu_buffer;
int cpu;
/* prevent another thread from changing buffer sizes */
mutex_lock(&buffer->mutex);
for_each_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
atomic_inc(&cpu_buffer->resize_disabled);
atomic_inc(&cpu_buffer->record_disabled);
}
/* Make sure all commits have finished */
synchronize_rcu();
for_each_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
reset_disabled_cpu_buffer(cpu_buffer);
atomic_dec(&cpu_buffer->record_disabled);
atomic_dec(&cpu_buffer->resize_disabled);
}
mutex_unlock(&buffer->mutex);
}
EXPORT_SYMBOL_GPL(ring_buffer_reset);
/**
* ring_buffer_empty - is the ring buffer empty?
* @buffer: The ring buffer to test
*/
bool ring_buffer_empty(struct trace_buffer *buffer)
{
struct ring_buffer_per_cpu *cpu_buffer;
unsigned long flags;
bool dolock;
bool ret;
int cpu;
/* yes this is racy, but if you don't like the race, lock the buffer */
for_each_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
local_irq_save(flags);
dolock = rb_reader_lock(cpu_buffer);
ret = rb_per_cpu_empty(cpu_buffer);
rb_reader_unlock(cpu_buffer, dolock);
local_irq_restore(flags);
if (!ret)
return false;
}
return true;
}
EXPORT_SYMBOL_GPL(ring_buffer_empty);
/**
* ring_buffer_empty_cpu - is a cpu buffer of a ring buffer empty?
* @buffer: The ring buffer
* @cpu: The CPU buffer to test
*/
bool ring_buffer_empty_cpu(struct trace_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
unsigned long flags;
bool dolock;
bool ret;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return true;
cpu_buffer = buffer->buffers[cpu];
local_irq_save(flags);
dolock = rb_reader_lock(cpu_buffer);
ret = rb_per_cpu_empty(cpu_buffer);
rb_reader_unlock(cpu_buffer, dolock);
local_irq_restore(flags);
return ret;
}
EXPORT_SYMBOL_GPL(ring_buffer_empty_cpu);
int ring_buffer_poll_writer(struct trace_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
unsigned long flags;
if (cpu != RING_BUFFER_ALL_CPUS) {
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return -EINVAL;
cpu_buffer = buffer->buffers[cpu];
raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
if (rb_read_writer_meta_page(cpu_buffer))
rb_wakeups(buffer, cpu_buffer);
raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
return 0;
}
/*
* Make sure all the ring buffers are up to date before we start reading
* them.
*/
for_each_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
rb_read_writer_meta_page(buffer->buffers[cpu]);
raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
}
for_each_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
if (rb_num_of_entries(cpu_buffer))
rb_wakeups(buffer, buffer->buffers[cpu]);
raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
}
return 0;
}
#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
/**
* ring_buffer_swap_cpu - swap a CPU buffer between two ring buffers
* @buffer_a: One buffer to swap with
* @buffer_b: The other buffer to swap with
* @cpu: the CPU of the buffers to swap
*
* This function is useful for tracers that want to take a "snapshot"
* of a CPU buffer and has another back up buffer lying around.
* it is expected that the tracer handles the cpu buffer not being
* used at the moment.
*/
int ring_buffer_swap_cpu(struct trace_buffer *buffer_a,
struct trace_buffer *buffer_b, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer_a;
struct ring_buffer_per_cpu *cpu_buffer_b;
int ret = -EINVAL;
if (!cpumask_test_cpu(cpu, buffer_a->cpumask) ||
!cpumask_test_cpu(cpu, buffer_b->cpumask))
goto out;
cpu_buffer_a = buffer_a->buffers[cpu];
cpu_buffer_b = buffer_b->buffers[cpu];
if (READ_ONCE(cpu_buffer_a->mapped) || READ_ONCE(cpu_buffer_b->mapped)) {
ret = -EBUSY;
goto out;
}
/* At least make sure the two buffers are somewhat the same */
if (cpu_buffer_a->nr_pages != cpu_buffer_b->nr_pages)
goto out;
ret = -EAGAIN;
if (atomic_read(&buffer_a->record_disabled))
goto out;
if (atomic_read(&buffer_b->record_disabled))
goto out;
if (atomic_read(&cpu_buffer_a->record_disabled))
goto out;
if (atomic_read(&cpu_buffer_b->record_disabled))
goto out;
/*
* We can't do a synchronize_rcu here because this
* function can be called in atomic context.
* Normally this will be called from the same CPU as cpu.
* If not it's up to the caller to protect this.
*/
atomic_inc(&cpu_buffer_a->record_disabled);
atomic_inc(&cpu_buffer_b->record_disabled);
ret = -EBUSY;
if (local_read(&cpu_buffer_a->committing))
goto out_dec;
if (local_read(&cpu_buffer_b->committing))
goto out_dec;
/*
* When resize is in progress, we cannot swap it because
* it will mess the state of the cpu buffer.
*/
if (atomic_read(&buffer_a->resizing))
goto out_dec;
if (atomic_read(&buffer_b->resizing))
goto out_dec;
buffer_a->buffers[cpu] = cpu_buffer_b;
buffer_b->buffers[cpu] = cpu_buffer_a;
cpu_buffer_b->buffer = buffer_a;
cpu_buffer_a->buffer = buffer_b;
ret = 0;
out_dec:
atomic_dec(&cpu_buffer_a->record_disabled);
atomic_dec(&cpu_buffer_b->record_disabled);
out:
return ret;
}
EXPORT_SYMBOL_GPL(ring_buffer_swap_cpu);
#endif /* CONFIG_RING_BUFFER_ALLOW_SWAP */
/**
* ring_buffer_alloc_read_page - allocate a page to read from buffer
* @buffer: the buffer to allocate for.
* @cpu: the cpu buffer to allocate.
*
* This function is used in conjunction with ring_buffer_read_page.
* When reading a full page from the ring buffer, these functions
* can be used to speed up the process. The calling function should
* allocate a few pages first with this function. Then when it
* needs to get pages from the ring buffer, it passes the result
* of this function into ring_buffer_read_page, which will swap
* the page that was allocated, with the read page of the buffer.
*
* Returns:
* The page allocated, or ERR_PTR
*/
void *ring_buffer_alloc_read_page(struct trace_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
struct buffer_data_page *bpage = NULL;
unsigned long flags;
struct page *page;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return ERR_PTR(-ENODEV);
cpu_buffer = buffer->buffers[cpu];
local_irq_save(flags);
arch_spin_lock(&cpu_buffer->lock);
if (cpu_buffer->free_page) {
bpage = cpu_buffer->free_page;
cpu_buffer->free_page = NULL;
}
arch_spin_unlock(&cpu_buffer->lock);
local_irq_restore(flags);
if (bpage)
goto out;
page = alloc_pages_node(cpu_to_node(cpu),
GFP_KERNEL | __GFP_NORETRY, 0);
if (!page)
return ERR_PTR(-ENOMEM);
bpage = page_address(page);
out:
rb_init_page(bpage);
return bpage;
}
EXPORT_SYMBOL_GPL(ring_buffer_alloc_read_page);
/**
* ring_buffer_free_read_page - free an allocated read page
* @buffer: the buffer the page was allocate for
* @cpu: the cpu buffer the page came from
* @data: the page to free
*
* Free a page allocated from ring_buffer_alloc_read_page.
*/
void ring_buffer_free_read_page(struct trace_buffer *buffer, int cpu, void *data)
{
struct ring_buffer_per_cpu *cpu_buffer;
struct buffer_data_page *bpage = data;
struct page *page = virt_to_page(bpage);
unsigned long flags;
if (!buffer || !buffer->buffers || !buffer->buffers[cpu])
return;
cpu_buffer = buffer->buffers[cpu];
/* If the page is still in use someplace else, we can't reuse it */
if (page_ref_count(page) > 1)
goto out;
local_irq_save(flags);
arch_spin_lock(&cpu_buffer->lock);
if (!cpu_buffer->free_page) {
cpu_buffer->free_page = bpage;
bpage = NULL;
}
arch_spin_unlock(&cpu_buffer->lock);
local_irq_restore(flags);
out:
free_page((unsigned long)bpage);
}
EXPORT_SYMBOL_GPL(ring_buffer_free_read_page);
/**
* ring_buffer_read_page - extract a page from the ring buffer
* @buffer: buffer to extract from
* @data_page: the page to use allocated from ring_buffer_alloc_read_page
* @len: amount to extract
* @cpu: the cpu of the buffer to extract
* @full: should the extraction only happen when the page is full.
*
* This function will pull out a page from the ring buffer and consume it.
* @data_page must be the address of the variable that was returned
* from ring_buffer_alloc_read_page. This is because the page might be used
* to swap with a page in the ring buffer.
*
* for example:
* rpage = ring_buffer_alloc_read_page(buffer, cpu);
* if (IS_ERR(rpage))
* return PTR_ERR(rpage);
* ret = ring_buffer_read_page(buffer, &rpage, len, cpu, 0);
* if (ret >= 0)
* process_page(rpage, ret);
*
* When @full is set, the function will not return true unless
* the writer is off the reader page.
*
* Note: it is up to the calling functions to handle sleeps and wakeups.
* The ring buffer can be used anywhere in the kernel and can not
* blindly call wake_up. The layer that uses the ring buffer must be
* responsible for that.
*
* Returns:
* >=0 if data has been transferred, returns the offset of consumed data.
* <0 if no data has been transferred.
*/
int ring_buffer_read_page(struct trace_buffer *buffer,
void **data_page, size_t len, int cpu, int full)
{
struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
struct ring_buffer_event *event;
struct buffer_data_page *bpage;
struct buffer_page *reader;
unsigned long missed_events;
unsigned long flags;
unsigned int commit;
unsigned int read;
u64 save_timestamp;
bool force_memcpy;
int ret = -1;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
goto out;
/*
* If len is not big enough to hold the page header, then
* we can not copy anything.
*/
if (len <= BUF_PAGE_HDR_SIZE)
goto out;
len -= BUF_PAGE_HDR_SIZE;
if (!data_page)
goto out;
bpage = *data_page;
if (!bpage)
goto out;
raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
reader = rb_get_reader_page(cpu_buffer);
if (!reader)
goto out_unlock;
event = rb_reader_event(cpu_buffer);
read = reader->read;
commit = rb_page_commit(reader);
/* Check if any events were dropped */
missed_events = cpu_buffer->lost_events;
force_memcpy = cpu_buffer->mapped || cpu_buffer->writer;
/*
* If this page has been partially read or
* if len is not big enough to read the rest of the page or
* a writer is still on the page, then
* we must copy the data from the page to the buffer.
* Otherwise, we can simply swap the page with the one passed in.
*/
if (read || (len < (commit - read)) ||
cpu_buffer->reader_page == cpu_buffer->commit_page ||
force_memcpy) {
struct buffer_data_page *rpage = cpu_buffer->reader_page->page;
unsigned int rpos = read;
unsigned int pos = 0;
unsigned int size;
/*
* If a full page is expected, this can still be returned
* if there's been a previous partial read and the
* rest of the page can be read and the commit page is off
* the reader page.
*/
if (full &&
(!read || (len < (commit - read)) ||
cpu_buffer->reader_page == cpu_buffer->commit_page))
goto out_unlock;
if (len > (commit - read))
len = (commit - read);
/* Always keep the time extend and data together */
size = rb_event_ts_length(event);
if (len < size)
goto out_unlock;
/* save the current timestamp, since the user will need it */
save_timestamp = cpu_buffer->read_stamp;
/* Need to copy one event at a time */
do {
/* We need the size of one event, because
* rb_advance_reader only advances by one event,
* whereas rb_event_ts_length may include the size of
* one or two events.
* We have already ensured there's enough space if this
* is a time extend. */
size = rb_event_length(event);
memcpy(bpage->data + pos, rpage->data + rpos, size);
len -= size;
rb_advance_reader(cpu_buffer);
rpos = reader->read;
pos += size;
if (rpos >= commit)
break;
event = rb_reader_event(cpu_buffer);
/* Always keep the time extend and data together */
size = rb_event_ts_length(event);
} while (len >= size);
/* update bpage */
local_set(&bpage->commit, pos);
bpage->time_stamp = save_timestamp;
/* we copied everything to the beginning */
read = 0;
} else {
/* update the entry counter */
cpu_buffer->read += rb_page_entries(reader);
cpu_buffer->read_bytes += rb_page_commit(reader);
/* swap the pages */
rb_init_page(bpage);
bpage = reader->page;
reader->page = *data_page;
local_set(&reader->write, 0);
local_set(&reader->entries, 0);
reader->read = 0;
*data_page = bpage;
/*
* Use the real_end for the data size,
* This gives us a chance to store the lost events
* on the page.
*/
if (reader->real_end)
local_set(&bpage->commit, reader->real_end);
}
ret = read;
cpu_buffer->lost_events = 0;
commit = local_read(&bpage->commit);
/*
* Set a flag in the commit field if we lost events
*/
if (missed_events) {
/* If there is room at the end of the page to save the
* missed events, then record it there.
*/
if (BUF_PAGE_SIZE - commit >= sizeof(missed_events)) {
memcpy(&bpage->data[commit], &missed_events,
sizeof(missed_events));
local_add(RB_MISSED_STORED, &bpage->commit);
commit += sizeof(missed_events);
}
local_add(RB_MISSED_EVENTS, &bpage->commit);
}
/*
* This page may be off to user land. Zero it out here.
*/
if (commit < BUF_PAGE_SIZE)
memset(&bpage->data[commit], 0, BUF_PAGE_SIZE - commit);
out_unlock:
raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
out:
return ret;
}
EXPORT_SYMBOL_GPL(ring_buffer_read_page);
static void rb_free_page_ids(struct ring_buffer_per_cpu *cpu_buffer)
{
int i;
for (i = 0; i < cpu_buffer->nr_pages + 1; i++)
virt_to_page((const void *)cpu_buffer->page_ids[i])->mapping = NULL;
kfree(cpu_buffer->page_ids);
cpu_buffer->page_ids = NULL;
}
static int rb_alloc_meta_page(struct ring_buffer_per_cpu *cpu_buffer)
{
if (cpu_buffer->meta_page)
return 0;
cpu_buffer->meta_page = page_to_virt(alloc_page(GFP_USER));
if (!cpu_buffer->meta_page)
return -ENOMEM;
return 0;
}
static void rb_free_meta_page(struct ring_buffer_per_cpu *cpu_buffer)
{
unsigned long addr = (unsigned long)cpu_buffer->meta_page;
virt_to_page((const void *)addr)->mapping = NULL;
free_page(addr);
cpu_buffer->meta_page = NULL;
}
static void rb_setup_ids_meta_page(struct ring_buffer_per_cpu *cpu_buffer,
unsigned long *page_ids)
{
struct ring_buffer_meta *meta = cpu_buffer->meta_page;
unsigned int nr_data_pages = cpu_buffer->nr_pages + 1;
struct buffer_page *first_page, *bpage;
int id = 0;
page_ids[id] = (unsigned long)cpu_buffer->reader_page->page;
cpu_buffer->reader_page->id = id++;
first_page = bpage = rb_set_head_page(cpu_buffer);
do {
if (id >= nr_data_pages) {
WARN_ON(1);
break;
}
page_ids[id] = (unsigned long)bpage->page;
bpage->id = id;
rb_inc_page(&bpage);
id++;
} while (bpage != first_page);
/* install page ID to kern VA translation */
cpu_buffer->page_ids = page_ids;
meta->meta_page_size = PAGE_SIZE;
meta->nr_data_pages = nr_data_pages;
meta->reader_page.id = cpu_buffer->reader_page->id;
rb_reset_meta_page(cpu_buffer);
}
static inline struct ring_buffer_per_cpu *
rb_get_mapped_buffer(struct trace_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return ERR_PTR(-EINVAL);
cpu_buffer = buffer->buffers[cpu];
mutex_lock(&cpu_buffer->mapping_lock);
if (!cpu_buffer->mapped) {
mutex_unlock(&cpu_buffer->mapping_lock);
return ERR_PTR(-ENODEV);
}
return cpu_buffer;
}
static inline void rb_put_mapped_buffer(struct ring_buffer_per_cpu *cpu_buffer)
{
mutex_unlock(&cpu_buffer->mapping_lock);
}
int ring_buffer_map(struct trace_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
unsigned long flags, *page_ids;
int err = 0;
if (!cpumask_test_cpu(cpu, buffer->cpumask) || buffer->writer)
return -EINVAL;
cpu_buffer = buffer->buffers[cpu];
mutex_lock(&cpu_buffer->mapping_lock);
if (cpu_buffer->mapped) {
WRITE_ONCE(cpu_buffer->mapped, cpu_buffer->mapped + 1);
goto unlock;
}
/* prevent another thread from changing buffer sizes */
mutex_lock(&buffer->mutex);
atomic_inc(&cpu_buffer->resize_disabled);
mutex_unlock(&buffer->mutex);
err = rb_alloc_meta_page(cpu_buffer);
if (err) {
atomic_dec(&cpu_buffer->resize_disabled);
goto unlock;
}
/* page_ids include the reader page while nr_pages does not */
page_ids = kzalloc(sizeof(*page_ids) * (cpu_buffer->nr_pages + 1),
GFP_KERNEL);
if (!page_ids) {
rb_free_meta_page(cpu_buffer);
atomic_dec(&cpu_buffer->resize_disabled);
err = -ENOMEM;
goto unlock;
}
/*
* Lock all readers to block any page swap until the page IDs are
* assigned.
*/
raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
rb_setup_ids_meta_page(cpu_buffer, page_ids);
/*
* Ensure the writer will observe the meta-page before
* cpu_buffer->mapped.
*/
smp_wmb();
WRITE_ONCE(cpu_buffer->mapped, 1);
/* Init meta_page values unless the writer did it already */
cmpxchg(&cpu_buffer->meta_page->entries, 0,
local_read(&cpu_buffer->entries));
cmpxchg(&cpu_buffer->meta_page->overrun, 0,
local_read(&cpu_buffer->overrun));
cmpxchg(&cpu_buffer->meta_page->pages_touched, 0,
local_read(&cpu_buffer->pages_touched));
cmpxchg(&cpu_buffer->meta_page->pages_lost, 0,
local_read(&cpu_buffer->pages_lost));
raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
unlock:
mutex_unlock(&cpu_buffer->mapping_lock);
return err;
}
int ring_buffer_unmap(struct trace_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
int err = 0;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return -EINVAL;
cpu_buffer = buffer->buffers[cpu];
mutex_lock(&cpu_buffer->mapping_lock);
if (!cpu_buffer->mapped) {
err = -ENODEV;
goto unlock;
}
WRITE_ONCE(cpu_buffer->mapped, cpu_buffer->mapped - 1);
if (!cpu_buffer->mapped) {
/* Wait the writer and readers to observe !mapped */
synchronize_rcu();
rb_free_page_ids(cpu_buffer);
rb_free_meta_page(cpu_buffer);
atomic_dec(&cpu_buffer->resize_disabled);
}
unlock:
mutex_unlock(&cpu_buffer->mapping_lock);
return err;
}
/*
* +--------------+
* | meta page | pgoff=0
* +--------------+
* | data page1 | page_ids=0
* +--------------+
* | data page2 | page_ids=1
* ...
*/
struct page *ring_buffer_map_fault(struct trace_buffer *buffer, int cpu,
unsigned long pgoff)
{
struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
if (!pgoff)
return virt_to_page((void *)cpu_buffer->meta_page);
pgoff--;
if (pgoff > cpu_buffer->nr_pages)
return NULL;
return virt_to_page((const void *)cpu_buffer->page_ids[pgoff]);
}
int ring_buffer_map_get_reader_page(struct trace_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
unsigned long reader_size, flags;
cpu_buffer = rb_get_mapped_buffer(buffer, cpu);
if (IS_ERR(cpu_buffer))
return (int)PTR_ERR(cpu_buffer);
raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
consume:
if (rb_per_cpu_empty(cpu_buffer))
goto out;
reader_size = rb_page_size(cpu_buffer->reader_page);
if (cpu_buffer->reader_page->read < reader_size) {
while (cpu_buffer->reader_page->read < reader_size)
rb_advance_reader(cpu_buffer);
goto out;
}
if (WARN_ON(!rb_get_reader_page(cpu_buffer)))
goto out;
goto consume;
out:
raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
rb_put_mapped_buffer(cpu_buffer);
return 0;
}
/*
* We only allocate new buffers, never free them if the CPU goes down.
* If we were to free the buffer, then the user would lose any trace that was in
* the buffer.
*/
int trace_rb_cpu_prepare(unsigned int cpu, struct hlist_node *node)
{
struct trace_buffer *buffer;
long nr_pages_same;
int cpu_i;
unsigned long nr_pages;
buffer = container_of(node, struct trace_buffer, node);
if (cpumask_test_cpu(cpu, buffer->cpumask))
return 0;
nr_pages = 0;
nr_pages_same = 1;
/* check if all cpu sizes are same */
for_each_buffer_cpu(buffer, cpu_i) {
/* fill in the size from first enabled cpu */
if (nr_pages == 0)
nr_pages = buffer->buffers[cpu_i]->nr_pages;
if (nr_pages != buffer->buffers[cpu_i]->nr_pages) {
nr_pages_same = 0;
break;
}
}
/* allocate minimum pages, user can later expand it */
if (!nr_pages_same)
nr_pages = 2;
buffer->buffers[cpu] =
rb_allocate_cpu_buffer(buffer, nr_pages, cpu);
if (!buffer->buffers[cpu]) {
WARN(1, "failed to allocate ring buffer on CPU %u\n",
cpu);
return -ENOMEM;
}
smp_wmb();
cpumask_set_cpu(cpu, buffer->cpumask);
return 0;
}
#ifdef CONFIG_RING_BUFFER_STARTUP_TEST
/*
* This is a basic integrity check of the ring buffer.
* Late in the boot cycle this test will run when configured in.
* It will kick off a thread per CPU that will go into a loop
* writing to the per cpu ring buffer various sizes of data.
* Some of the data will be large items, some small.
*
* Another thread is created that goes into a spin, sending out
* IPIs to the other CPUs to also write into the ring buffer.
* this is to test the nesting ability of the buffer.
*
* Basic stats are recorded and reported. If something in the
* ring buffer should happen that's not expected, a big warning
* is displayed and all ring buffers are disabled.
*/
static struct task_struct *rb_threads[NR_CPUS] __initdata;
struct rb_test_data {
struct trace_buffer *buffer;
unsigned long events;
unsigned long bytes_written;
unsigned long bytes_alloc;
unsigned long bytes_dropped;
unsigned long events_nested;
unsigned long bytes_written_nested;
unsigned long bytes_alloc_nested;
unsigned long bytes_dropped_nested;
int min_size_nested;
int max_size_nested;
int max_size;
int min_size;
int cpu;
int cnt;
};
static struct rb_test_data rb_data[NR_CPUS] __initdata;
/* 1 meg per cpu */
#define RB_TEST_BUFFER_SIZE 1048576
static char rb_string[] __initdata =
"abcdefghijklmnopqrstuvwxyz1234567890!@#$%^&*()?+\\"
"?+|:';\",.<>/?abcdefghijklmnopqrstuvwxyz1234567890"
"!@#$%^&*()?+\\?+|:';\",.<>/?abcdefghijklmnopqrstuv";
static bool rb_test_started __initdata;
struct rb_item {
int size;
char str[];
};
static __init int rb_write_something(struct rb_test_data *data, bool nested)
{
struct ring_buffer_event *event;
struct rb_item *item;
bool started;
int event_len;
int size;
int len;
int cnt;
/* Have nested writes different that what is written */
cnt = data->cnt + (nested ? 27 : 0);
/* Multiply cnt by ~e, to make some unique increment */
size = (cnt * 68 / 25) % (sizeof(rb_string) - 1);
len = size + sizeof(struct rb_item);
started = rb_test_started;
/* read rb_test_started before checking buffer enabled */
smp_rmb();
event = ring_buffer_lock_reserve(data->buffer, len);
if (!event) {
/* Ignore dropped events before test starts. */
if (started) {
if (nested)
data->bytes_dropped += len;
else
data->bytes_dropped_nested += len;
}
return len;
}
event_len = ring_buffer_event_length(event);
if (RB_WARN_ON(data->buffer, event_len < len))
goto out;
item = ring_buffer_event_data(event);
item->size = size;
memcpy(item->str, rb_string, size);
if (nested) {
data->bytes_alloc_nested += event_len;
data->bytes_written_nested += len;
data->events_nested++;
if (!data->min_size_nested || len < data->min_size_nested)
data->min_size_nested = len;
if (len > data->max_size_nested)
data->max_size_nested = len;
} else {
data->bytes_alloc += event_len;
data->bytes_written += len;
data->events++;
if (!data->min_size || len < data->min_size)
data->max_size = len;
if (len > data->max_size)
data->max_size = len;
}
out:
ring_buffer_unlock_commit(data->buffer);
return 0;
}
static __init int rb_test(void *arg)
{
struct rb_test_data *data = arg;
while (!kthread_should_stop()) {
rb_write_something(data, false);
data->cnt++;
set_current_state(TASK_INTERRUPTIBLE);
/* Now sleep between a min of 100-300us and a max of 1ms */
usleep_range(((data->cnt % 3) + 1) * 100, 1000);
}
return 0;
}
static __init void rb_ipi(void *ignore)
{
struct rb_test_data *data;
int cpu = smp_processor_id();
data = &rb_data[cpu];
rb_write_something(data, true);
}
static __init int rb_hammer_test(void *arg)
{
while (!kthread_should_stop()) {
/* Send an IPI to all cpus to write data! */
smp_call_function(rb_ipi, NULL, 1);
/* No sleep, but for non preempt, let others run */
schedule();
}
return 0;
}
static __init int test_ringbuffer(void)
{
struct task_struct *rb_hammer;
struct trace_buffer *buffer;
int cpu;
int ret = 0;
if (security_locked_down(LOCKDOWN_TRACEFS)) {
pr_warn("Lockdown is enabled, skipping ring buffer tests\n");
return 0;
}
pr_info("Running ring buffer tests...\n");
buffer = ring_buffer_alloc(RB_TEST_BUFFER_SIZE, RB_FL_OVERWRITE);
if (WARN_ON(!buffer))
return 0;
/* Disable buffer so that threads can't write to it yet */
ring_buffer_record_off(buffer);
for_each_online_cpu(cpu) {
rb_data[cpu].buffer = buffer;
rb_data[cpu].cpu = cpu;
rb_data[cpu].cnt = cpu;
rb_threads[cpu] = kthread_run_on_cpu(rb_test, &rb_data[cpu],
cpu, "rbtester/%u");
if (WARN_ON(IS_ERR(rb_threads[cpu]))) {
pr_cont("FAILED\n");
ret = PTR_ERR(rb_threads[cpu]);
goto out_free;
}
}
/* Now create the rb hammer! */
rb_hammer = kthread_run(rb_hammer_test, NULL, "rbhammer");
if (WARN_ON(IS_ERR(rb_hammer))) {
pr_cont("FAILED\n");
ret = PTR_ERR(rb_hammer);
goto out_free;
}
ring_buffer_record_on(buffer);
/*
* Show buffer is enabled before setting rb_test_started.
* Yes there's a small race window where events could be
* dropped and the thread wont catch it. But when a ring
* buffer gets enabled, there will always be some kind of
* delay before other CPUs see it. Thus, we don't care about
* those dropped events. We care about events dropped after
* the threads see that the buffer is active.
*/
smp_wmb();
rb_test_started = true;
set_current_state(TASK_INTERRUPTIBLE);
/* Just run for 10 seconds */;
schedule_timeout(10 * HZ);
kthread_stop(rb_hammer);
out_free:
for_each_online_cpu(cpu) {
if (!rb_threads[cpu])
break;
kthread_stop(rb_threads[cpu]);
}
if (ret) {
ring_buffer_free(buffer);
return ret;
}
/* Report! */
pr_info("finished\n");
for_each_online_cpu(cpu) {
struct ring_buffer_event *event;
struct rb_test_data *data = &rb_data[cpu];
struct rb_item *item;
unsigned long total_events;
unsigned long total_dropped;
unsigned long total_written;
unsigned long total_alloc;
unsigned long total_read = 0;
unsigned long total_size = 0;
unsigned long total_len = 0;
unsigned long total_lost = 0;
unsigned long lost;
int big_event_size;
int small_event_size;
ret = -1;
total_events = data->events + data->events_nested;
total_written = data->bytes_written + data->bytes_written_nested;
total_alloc = data->bytes_alloc + data->bytes_alloc_nested;
total_dropped = data->bytes_dropped + data->bytes_dropped_nested;
big_event_size = data->max_size + data->max_size_nested;
small_event_size = data->min_size + data->min_size_nested;
pr_info("CPU %d:\n", cpu);
pr_info(" events: %ld\n", total_events);
pr_info(" dropped bytes: %ld\n", total_dropped);
pr_info(" alloced bytes: %ld\n", total_alloc);
pr_info(" written bytes: %ld\n", total_written);
pr_info(" biggest event: %d\n", big_event_size);
pr_info(" smallest event: %d\n", small_event_size);
if (RB_WARN_ON(buffer, total_dropped))
break;
ret = 0;
while ((event = ring_buffer_consume(buffer, cpu, NULL, &lost))) {
total_lost += lost;
item = ring_buffer_event_data(event);
total_len += ring_buffer_event_length(event);
total_size += item->size + sizeof(struct rb_item);
if (memcmp(&item->str[0], rb_string, item->size) != 0) {
pr_info("FAILED!\n");
pr_info("buffer had: %.*s\n", item->size, item->str);
pr_info("expected: %.*s\n", item->size, rb_string);
RB_WARN_ON(buffer, 1);
ret = -1;
break;
}
total_read++;
}
if (ret)
break;
ret = -1;
pr_info(" read events: %ld\n", total_read);
pr_info(" lost events: %ld\n", total_lost);
pr_info(" total events: %ld\n", total_lost + total_read);
pr_info(" recorded len bytes: %ld\n", total_len);
pr_info(" recorded size bytes: %ld\n", total_size);
if (total_lost) {
pr_info(" With dropped events, record len and size may not match\n"
" alloced and written from above\n");
} else {
if (RB_WARN_ON(buffer, total_len != total_alloc ||
total_size != total_written))
break;
}
if (RB_WARN_ON(buffer, total_lost + total_read != total_events))
break;
ret = 0;
}
if (!ret)
pr_info("Ring buffer PASSED!\n");
ring_buffer_free(buffer);
return 0;
}
late_initcall(test_ringbuffer);
#endif /* CONFIG_RING_BUFFER_STARTUP_TEST */