Merge tag 'printk-for-6.9' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux
Pull printk updates from Petr Mladek:
"Improve the behavior during panic. The issues were found when testing
the ongoing changes introducing atomic consoles and printk kthreads:
- pr_flush() has to wait for the last reserved record instead of the
last finalized one. Note that records are finalized in random order
when generated by more CPUs in parallel.
- Ignore non-finalized records during panic(). Messages printed on
panic-CPU are always finalized. Messages printed by other CPUs
might never be finalized when the CPUs get stopped.
- Block new printk() calls on non-panic CPUs completely. Backtraces
are printed before entering the panic mode. Later messages would
just mess information printed by the panic CPU.
- Do not take console_lock in console_flush_on_panic() at all. The
original code did try_lock()/console_unlock(). The unlock part
might cause a deadlock when panic() happened in a scheduler code.
- Fix conversion of 64-bit sequence number for 32-bit atomic
operations"
* tag 'printk-for-6.9' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux:
dump_stack: Do not get cpu_sync for panic CPU
panic: Flush kernel log buffer at the end
printk: Avoid non-panic CPUs writing to ringbuffer
printk: Disable passing console lock owner completely during panic()
printk: ringbuffer: Skip non-finalized records in panic
printk: Wait for all reserved records with pr_flush()
printk: ringbuffer: Cleanup reader terminology
printk: Add this_cpu_in_panic()
printk: For @suppress_panic_printk check for other CPU in panic
printk: ringbuffer: Clarify special lpos values
printk: ringbuffer: Do not skip non-finalized records with prb_next_seq()
printk: Use prb_first_seq() as base for 32bit seq macros
printk: Adjust mapping for 32bit seq macros
printk: nbcon: Relocate 32bit seq macros
diff --git a/include/linux/printk.h b/include/linux/printk.h
index 8ef499a..955e318 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -273,6 +273,8 @@
}
#endif
+bool this_cpu_in_panic(void);
+
#ifdef CONFIG_SMP
extern int __printk_cpu_sync_try_get(void);
extern void __printk_cpu_sync_wait(void);
diff --git a/kernel/panic.c b/kernel/panic.c
index 2807639..f22d8f3 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -446,6 +446,14 @@
/* Do not scroll important messages printed above */
suppress_printk = 1;
+
+ /*
+ * The final messages may not have been printed if in a context that
+ * defers printing (such as NMI) and irq_work is not available.
+ * Explicitly flush the kernel log buffer one last time.
+ */
+ console_flush_on_panic(CONSOLE_FLUSH_PENDING);
+
local_irq_enable();
for (i = 0; ; i += PANIC_TIMER_STEP) {
touch_softlockup_watchdog();
diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c
index b960771..c8093bc 100644
--- a/kernel/printk/nbcon.c
+++ b/kernel/printk/nbcon.c
@@ -140,39 +140,6 @@
return atomic_try_cmpxchg(&ACCESS_PRIVATE(con, nbcon_state), &cur->atom, new->atom);
}
-#ifdef CONFIG_64BIT
-
-#define __seq_to_nbcon_seq(seq) (seq)
-#define __nbcon_seq_to_seq(seq) (seq)
-
-#else /* CONFIG_64BIT */
-
-#define __seq_to_nbcon_seq(seq) ((u32)seq)
-
-static inline u64 __nbcon_seq_to_seq(u32 nbcon_seq)
-{
- u64 seq;
- u64 rb_next_seq;
-
- /*
- * The provided sequence is only the lower 32 bits of the ringbuffer
- * sequence. It needs to be expanded to 64bit. Get the next sequence
- * number from the ringbuffer and fold it.
- *
- * Having a 32bit representation in the console is sufficient.
- * If a console ever gets more than 2^31 records behind
- * the ringbuffer then this is the least of the problems.
- *
- * Also the access to the ring buffer is always safe.
- */
- rb_next_seq = prb_next_seq(prb);
- seq = rb_next_seq - ((u32)rb_next_seq - nbcon_seq);
-
- return seq;
-}
-
-#endif /* CONFIG_64BIT */
-
/**
* nbcon_seq_read - Read the current console sequence
* @con: Console to read the sequence of
@@ -183,7 +150,7 @@
{
unsigned long nbcon_seq = atomic_long_read(&ACCESS_PRIVATE(con, nbcon_seq));
- return __nbcon_seq_to_seq(nbcon_seq);
+ return __ulseq_to_u64seq(prb, nbcon_seq);
}
/**
@@ -204,7 +171,7 @@
*/
u64 valid_seq = max_t(u64, seq, prb_first_valid_seq(prb));
- atomic_long_set(&ACCESS_PRIVATE(con, nbcon_seq), __seq_to_nbcon_seq(valid_seq));
+ atomic_long_set(&ACCESS_PRIVATE(con, nbcon_seq), __u64seq_to_ulseq(valid_seq));
/* Clear con->seq since nbcon consoles use con->nbcon_seq instead. */
con->seq = 0;
@@ -223,11 +190,11 @@
*/
static void nbcon_seq_try_update(struct nbcon_context *ctxt, u64 new_seq)
{
- unsigned long nbcon_seq = __seq_to_nbcon_seq(ctxt->seq);
+ unsigned long nbcon_seq = __u64seq_to_ulseq(ctxt->seq);
struct console *con = ctxt->console;
if (atomic_long_try_cmpxchg(&ACCESS_PRIVATE(con, nbcon_seq), &nbcon_seq,
- __seq_to_nbcon_seq(new_seq))) {
+ __u64seq_to_ulseq(new_seq))) {
ctxt->seq = new_seq;
} else {
ctxt->seq = nbcon_seq_read(con);
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 1c6e7df..b06f63e 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -347,6 +347,29 @@
return unlikely(atomic_read(&panic_cpu) != PANIC_CPU_INVALID);
}
+/* Return true if a panic is in progress on the current CPU. */
+bool this_cpu_in_panic(void)
+{
+ /*
+ * We can use raw_smp_processor_id() here because it is impossible for
+ * the task to be migrated to the panic_cpu, or away from it. If
+ * panic_cpu has already been set, and we're not currently executing on
+ * that CPU, then we never will be.
+ */
+ return unlikely(atomic_read(&panic_cpu) == raw_smp_processor_id());
+}
+
+/*
+ * Return true if a panic is in progress on a remote CPU.
+ *
+ * On true, the local CPU should immediately release any printing resources
+ * that may be needed by the panic CPU.
+ */
+bool other_cpu_in_panic(void)
+{
+ return (panic_in_progress() && !this_cpu_in_panic());
+}
+
/*
* This is used for debugging the mess that is the VT code by
* keeping track if we have the console semaphore held. It's
@@ -439,12 +462,6 @@
static DEFINE_MUTEX(syslog_lock);
#ifdef CONFIG_PRINTK
-/*
- * During panic, heavy printk by other CPUs can delay the
- * panic and risk deadlock on console resources.
- */
-static int __read_mostly suppress_panic_printk;
-
DECLARE_WAIT_QUEUE_HEAD(log_wait);
/* All 3 protected by @syslog_lock. */
/* the next printk record to read by syslog(READ) or /proc/kmsg */
@@ -1835,10 +1852,23 @@
*/
static void console_lock_spinning_enable(void)
{
+ /*
+ * Do not use spinning in panic(). The panic CPU wants to keep the lock.
+ * Non-panic CPUs abandon the flush anyway.
+ *
+ * Just keep the lockdep annotation. The panic-CPU should avoid
+ * taking console_owner_lock because it might cause a deadlock.
+ * This looks like the easiest way how to prevent false lockdep
+ * reports without handling races a lockless way.
+ */
+ if (panic_in_progress())
+ goto lockdep;
+
raw_spin_lock(&console_owner_lock);
console_owner = current;
raw_spin_unlock(&console_owner_lock);
+lockdep:
/* The waiter may spin on us after setting console_owner */
spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_);
}
@@ -1863,6 +1893,22 @@
{
int waiter;
+ /*
+ * Ignore spinning waiters during panic() because they might get stopped
+ * or blocked at any time,
+ *
+ * It is safe because nobody is allowed to start spinning during panic
+ * in the first place. If there has been a waiter then non panic CPUs
+ * might stay spinning. They would get stopped anyway. The panic context
+ * will never start spinning and an interrupted spin on panic CPU will
+ * never continue.
+ */
+ if (panic_in_progress()) {
+ /* Keep lockdep happy. */
+ spin_release(&console_owner_dep_map, _THIS_IP_);
+ return 0;
+ }
+
raw_spin_lock(&console_owner_lock);
waiter = READ_ONCE(console_waiter);
console_owner = NULL;
@@ -2259,8 +2305,12 @@
if (unlikely(suppress_printk))
return 0;
- if (unlikely(suppress_panic_printk) &&
- atomic_read(&panic_cpu) != raw_smp_processor_id())
+ /*
+ * The messages on the panic CPU are the most important. If
+ * non-panic CPUs are generating any messages, they will be
+ * silently dropped.
+ */
+ if (other_cpu_in_panic())
return 0;
if (level == LOGLEVEL_SCHED) {
@@ -2590,26 +2640,6 @@
return 0;
}
-/*
- * Return true if a panic is in progress on a remote CPU.
- *
- * On true, the local CPU should immediately release any printing resources
- * that may be needed by the panic CPU.
- */
-bool other_cpu_in_panic(void)
-{
- if (!panic_in_progress())
- return false;
-
- /*
- * We can use raw_smp_processor_id() here because it is impossible for
- * the task to be migrated to the panic_cpu, or away from it. If
- * panic_cpu has already been set, and we're not currently executing on
- * that CPU, then we never will be.
- */
- return atomic_read(&panic_cpu) != raw_smp_processor_id();
-}
-
/**
* console_lock - block the console subsystem from printing
*
@@ -2765,8 +2795,6 @@
bool printk_get_next_message(struct printk_message *pmsg, u64 seq,
bool is_extended, bool may_suppress)
{
- static int panic_console_dropped;
-
struct printk_buffers *pbufs = pmsg->pbufs;
const size_t scratchbuf_sz = sizeof(pbufs->scratchbuf);
const size_t outbuf_sz = sizeof(pbufs->outbuf);
@@ -2794,17 +2822,6 @@
pmsg->seq = r.info->seq;
pmsg->dropped = r.info->seq - seq;
- /*
- * Check for dropped messages in panic here so that printk
- * suppression can occur as early as possible if necessary.
- */
- if (pmsg->dropped &&
- panic_in_progress() &&
- panic_console_dropped++ > 10) {
- suppress_panic_printk = 1;
- pr_warn_once("Too many dropped messages. Suppress messages on non-panic CPUs to prevent livelock.\n");
- }
-
/* Skip record that has level above the console loglevel. */
if (may_suppress && suppress_message_printing(r.info->level))
goto out;
@@ -3750,7 +3767,7 @@
might_sleep();
- seq = prb_next_seq(prb);
+ seq = prb_next_reserve_seq(prb);
/* Flush the consoles so that records up to @seq are printed. */
console_lock();
diff --git a/kernel/printk/printk_ringbuffer.c b/kernel/printk/printk_ringbuffer.c
index fde3386..88e8f3a 100644
--- a/kernel/printk/printk_ringbuffer.c
+++ b/kernel/printk/printk_ringbuffer.c
@@ -6,6 +6,7 @@
#include <linux/errno.h>
#include <linux/bug.h>
#include "printk_ringbuffer.h"
+#include "internal.h"
/**
* DOC: printk_ringbuffer overview
@@ -303,6 +304,9 @@
*
* desc_push_tail:B / desc_reserve:D
* set descriptor reusable (state), then push descriptor tail (id)
+ *
+ * desc_update_last_finalized:A / desc_last_finalized_seq:A
+ * store finalized record, then set new highest finalized sequence number
*/
#define DATA_SIZE(data_ring) _DATA_SIZE((data_ring)->size_bits)
@@ -1030,9 +1034,13 @@
unsigned long next_lpos;
if (size == 0) {
- /* Specify a data-less block. */
- blk_lpos->begin = NO_LPOS;
- blk_lpos->next = NO_LPOS;
+ /*
+ * Data blocks are not created for empty lines. Instead, the
+ * reader will recognize these special lpos values and handle
+ * it appropriately.
+ */
+ blk_lpos->begin = EMPTY_LINE_LPOS;
+ blk_lpos->next = EMPTY_LINE_LPOS;
return NULL;
}
@@ -1210,10 +1218,18 @@
/* Data-less data block description. */
if (BLK_DATALESS(blk_lpos)) {
- if (blk_lpos->begin == NO_LPOS && blk_lpos->next == NO_LPOS) {
+ /*
+ * Records that are just empty lines are also valid, even
+ * though they do not have a data block. For such records
+ * explicitly return empty string data to signify success.
+ */
+ if (blk_lpos->begin == EMPTY_LINE_LPOS &&
+ blk_lpos->next == EMPTY_LINE_LPOS) {
*data_size = 0;
return "";
}
+
+ /* Data lost, invalid, or otherwise unavailable. */
return NULL;
}
@@ -1442,19 +1458,117 @@
}
/*
+ * @last_finalized_seq value guarantees that all records up to and including
+ * this sequence number are finalized and can be read. The only exception are
+ * too old records which have already been overwritten.
+ *
+ * It is also guaranteed that @last_finalized_seq only increases.
+ *
+ * Be aware that finalized records following non-finalized records are not
+ * reported because they are not yet available to the reader. For example,
+ * a new record stored via printk() will not be available to a printer if
+ * it follows a record that has not been finalized yet. However, once that
+ * non-finalized record becomes finalized, @last_finalized_seq will be
+ * appropriately updated and the full set of finalized records will be
+ * available to the printer. And since each printk() caller will either
+ * directly print or trigger deferred printing of all available unprinted
+ * records, all printk() messages will get printed.
+ */
+static u64 desc_last_finalized_seq(struct printk_ringbuffer *rb)
+{
+ struct prb_desc_ring *desc_ring = &rb->desc_ring;
+ unsigned long ulseq;
+
+ /*
+ * Guarantee the sequence number is loaded before loading the
+ * associated record in order to guarantee that the record can be
+ * seen by this CPU. This pairs with desc_update_last_finalized:A.
+ */
+ ulseq = atomic_long_read_acquire(&desc_ring->last_finalized_seq
+ ); /* LMM(desc_last_finalized_seq:A) */
+
+ return __ulseq_to_u64seq(rb, ulseq);
+}
+
+static bool _prb_read_valid(struct printk_ringbuffer *rb, u64 *seq,
+ struct printk_record *r, unsigned int *line_count);
+
+/*
+ * Check if there are records directly following @last_finalized_seq that are
+ * finalized. If so, update @last_finalized_seq to the latest of these
+ * records. It is not allowed to skip over records that are not yet finalized.
+ */
+static void desc_update_last_finalized(struct printk_ringbuffer *rb)
+{
+ struct prb_desc_ring *desc_ring = &rb->desc_ring;
+ u64 old_seq = desc_last_finalized_seq(rb);
+ unsigned long oldval;
+ unsigned long newval;
+ u64 finalized_seq;
+ u64 try_seq;
+
+try_again:
+ finalized_seq = old_seq;
+ try_seq = finalized_seq + 1;
+
+ /* Try to find later finalized records. */
+ while (_prb_read_valid(rb, &try_seq, NULL, NULL)) {
+ finalized_seq = try_seq;
+ try_seq++;
+ }
+
+ /* No update needed if no later finalized record was found. */
+ if (finalized_seq == old_seq)
+ return;
+
+ oldval = __u64seq_to_ulseq(old_seq);
+ newval = __u64seq_to_ulseq(finalized_seq);
+
+ /*
+ * Set the sequence number of a later finalized record that has been
+ * seen.
+ *
+ * Guarantee the record data is visible to other CPUs before storing
+ * its sequence number. This pairs with desc_last_finalized_seq:A.
+ *
+ * Memory barrier involvement:
+ *
+ * If desc_last_finalized_seq:A reads from
+ * desc_update_last_finalized:A, then desc_read:A reads from
+ * _prb_commit:B.
+ *
+ * Relies on:
+ *
+ * RELEASE from _prb_commit:B to desc_update_last_finalized:A
+ * matching
+ * ACQUIRE from desc_last_finalized_seq:A to desc_read:A
+ *
+ * Note: _prb_commit:B and desc_update_last_finalized:A can be
+ * different CPUs. However, the desc_update_last_finalized:A
+ * CPU (which performs the release) must have previously seen
+ * _prb_commit:B.
+ */
+ if (!atomic_long_try_cmpxchg_release(&desc_ring->last_finalized_seq,
+ &oldval, newval)) { /* LMM(desc_update_last_finalized:A) */
+ old_seq = __ulseq_to_u64seq(rb, oldval);
+ goto try_again;
+ }
+}
+
+/*
* Attempt to finalize a specified descriptor. If this fails, the descriptor
* is either already final or it will finalize itself when the writer commits.
*/
-static void desc_make_final(struct prb_desc_ring *desc_ring, unsigned long id)
+static void desc_make_final(struct printk_ringbuffer *rb, unsigned long id)
{
+ struct prb_desc_ring *desc_ring = &rb->desc_ring;
unsigned long prev_state_val = DESC_SV(id, desc_committed);
struct prb_desc *d = to_desc(desc_ring, id);
- atomic_long_cmpxchg_relaxed(&d->state_var, prev_state_val,
- DESC_SV(id, desc_finalized)); /* LMM(desc_make_final:A) */
-
- /* Best effort to remember the last finalized @id. */
- atomic_long_set(&desc_ring->last_finalized_id, id);
+ if (atomic_long_try_cmpxchg_relaxed(&d->state_var, &prev_state_val,
+ DESC_SV(id, desc_finalized))) { /* LMM(desc_make_final:A) */
+ desc_update_last_finalized(rb);
+ }
}
/**
@@ -1550,7 +1664,7 @@
* readers. (For seq==0 there is no previous descriptor.)
*/
if (info->seq > 0)
- desc_make_final(desc_ring, DESC_ID(id - 1));
+ desc_make_final(rb, DESC_ID(id - 1));
r->text_buf = data_alloc(rb, r->text_buf_size, &d->text_blk_lpos, id);
/* If text data allocation fails, a data-less record is committed. */
@@ -1643,7 +1757,7 @@
*/
head_id = atomic_long_read(&desc_ring->head_id); /* LMM(prb_commit:A) */
if (head_id != e->id)
- desc_make_final(desc_ring, e->id);
+ desc_make_final(e->rb, e->id);
}
/**
@@ -1663,12 +1777,9 @@
*/
void prb_final_commit(struct prb_reserved_entry *e)
{
- struct prb_desc_ring *desc_ring = &e->rb->desc_ring;
-
_prb_commit(e, desc_finalized);
- /* Best effort to remember the last finalized @id. */
- atomic_long_set(&desc_ring->last_finalized_id, e->id);
+ desc_update_last_finalized(e->rb);
}
/*
@@ -1832,7 +1943,7 @@
}
/* Get the sequence number of the tail descriptor. */
-static u64 prb_first_seq(struct printk_ringbuffer *rb)
+u64 prb_first_seq(struct printk_ringbuffer *rb)
{
struct prb_desc_ring *desc_ring = &rb->desc_ring;
enum desc_state d_state;
@@ -1875,12 +1986,123 @@
return seq;
}
-/*
- * Non-blocking read of a record. Updates @seq to the last finalized record
- * (which may have no data available).
+/**
+ * prb_next_reserve_seq() - Get the sequence number after the most recently
+ * reserved record.
*
- * See the description of prb_read_valid() and prb_read_valid_info()
- * for details.
+ * @rb: The ringbuffer to get the sequence number from.
+ *
+ * This is the public function available to readers to see what sequence
+ * number will be assigned to the next reserved record.
+ *
+ * Note that depending on the situation, this value can be equal to or
+ * higher than the sequence number returned by prb_next_seq().
+ *
+ * Context: Any context.
+ * Return: The sequence number that will be assigned to the next record
+ * reserved.
+ */
+u64 prb_next_reserve_seq(struct printk_ringbuffer *rb)
+{
+ struct prb_desc_ring *desc_ring = &rb->desc_ring;
+ unsigned long last_finalized_id;
+ atomic_long_t *state_var;
+ u64 last_finalized_seq;
+ unsigned long head_id;
+ struct prb_desc desc;
+ unsigned long diff;
+ struct prb_desc *d;
+ int err;
+
+ /*
+ * It may not be possible to read a sequence number for @head_id.
+ * So the ID of @last_finailzed_seq is used to calculate what the
+ * sequence number of @head_id will be.
+ */
+
+try_again:
+ last_finalized_seq = desc_last_finalized_seq(rb);
+
+ /*
+ * @head_id is loaded after @last_finalized_seq to ensure that
+ * it points to the record with @last_finalized_seq or newer.
+ *
+ * Memory barrier involvement:
+ *
+ * If desc_last_finalized_seq:A reads from
+ * desc_update_last_finalized:A, then
+ * prb_next_reserve_seq:A reads from desc_reserve:D.
+ *
+ * Relies on:
+ *
+ * RELEASE from desc_reserve:D to desc_update_last_finalized:A
+ * matching
+ * ACQUIRE from desc_last_finalized_seq:A to prb_next_reserve_seq:A
+ *
+ * Note: desc_reserve:D and desc_update_last_finalized:A can be
+ * different CPUs. However, the desc_update_last_finalized:A CPU
+ * (which performs the release) must have previously seen
+ * desc_read:C, which implies desc_reserve:D can be seen.
+ */
+ head_id = atomic_long_read(&desc_ring->head_id); /* LMM(prb_next_reserve_seq:A) */
+
+ d = to_desc(desc_ring, last_finalized_seq);
+ state_var = &d->state_var;
+
+ /* Extract the ID, used to specify the descriptor to read. */
+ last_finalized_id = DESC_ID(atomic_long_read(state_var));
+
+ /* Ensure @last_finalized_id is correct. */
+ err = desc_read_finalized_seq(desc_ring, last_finalized_id, last_finalized_seq, &desc);
+
+ if (err == -EINVAL) {
+ if (last_finalized_seq == 0) {
+ /*
+ * No record has been finalized or even reserved yet.
+ *
+ * The @head_id is initialized such that the first
+ * increment will yield the first record (seq=0).
+ * Handle it separately to avoid a negative @diff
+ * below.
+ */
+ if (head_id == DESC0_ID(desc_ring->count_bits))
+ return 0;
+
+ /*
+ * One or more descriptors are already reserved. Use
+ * the descriptor ID of the first one (@seq=0) for
+ * the @diff below.
+ */
+ last_finalized_id = DESC0_ID(desc_ring->count_bits) + 1;
+ } else {
+ /* Record must have been overwritten. Try again. */
+ goto try_again;
+ }
+ }
+
+ /* Diff of known descriptor IDs to compute related sequence numbers. */
+ diff = head_id - last_finalized_id;
+
+ /*
+ * @head_id points to the most recently reserved record, but this
+ * function returns the sequence number that will be assigned to the
+ * next (not yet reserved) record. Thus +1 is needed.
+ */
+ return (last_finalized_seq + diff + 1);
+}
+
+/*
+ * Non-blocking read of a record.
+ *
+ * On success @seq is updated to the record that was read and (if provided)
+ * @r and @line_count will contain the read/calculated data.
+ *
+ * On failure @seq is updated to a record that is not yet available to the
+ * reader, but it will be the next record available to the reader.
+ *
+ * Note: When the current CPU is in panic, this function will skip over any
+ * non-existent/non-finalized records in order to allow the panic CPU
+ * to print any and all records that have been finalized.
*/
static bool _prb_read_valid(struct printk_ringbuffer *rb, u64 *seq,
struct printk_record *r, unsigned int *line_count)
@@ -1899,12 +2121,32 @@
*seq = tail_seq;
} else if (err == -ENOENT) {
- /* Record exists, but no data available. Skip. */
+ /* Record exists, but the data was lost. Skip. */
(*seq)++;
} else {
- /* Non-existent/non-finalized record. Must stop. */
- return false;
+ /*
+ * Non-existent/non-finalized record. Must stop.
+ *
+ * For panic situations it cannot be expected that
+ * non-finalized records will become finalized. But
+ * there may be other finalized records beyond that
+ * need to be printed for a panic situation. If this
+ * is the panic CPU, skip this
+ * non-existent/non-finalized record unless it is
+ * at or beyond the head, in which case it is not
+ * possible to continue.
+ *
+ * Note that new messages printed on panic CPU are
+ * finalized when we are here. The only exception
+ * might be the last message without trailing newline.
+ * But it would have the sequence number returned
+ * by "prb_next_reserve_seq() - 1".
+ */
+ if (this_cpu_in_panic() && ((*seq + 1) < prb_next_reserve_seq(rb)))
+ (*seq)++;
+ else
+ return false;
}
}
@@ -1932,7 +2174,7 @@
* On success, the reader must check r->info.seq to see which record was
* actually read. This allows the reader to detect dropped records.
*
- * Failure means @seq refers to a not yet written record.
+ * Failure means @seq refers to a record not yet available to the reader.
*/
bool prb_read_valid(struct printk_ringbuffer *rb, u64 seq,
struct printk_record *r)
@@ -1962,7 +2204,7 @@
* On success, the reader must check info->seq to see which record meta data
* was actually read. This allows the reader to detect dropped records.
*
- * Failure means @seq refers to a not yet written record.
+ * Failure means @seq refers to a record not yet available to the reader.
*/
bool prb_read_valid_info(struct printk_ringbuffer *rb, u64 seq,
struct printk_info *info, unsigned int *line_count)
@@ -2008,7 +2250,9 @@
* newest sequence number available to readers will be.
*
* This provides readers a sequence number to jump to if all currently
- * available records should be skipped.
+ * available records should be skipped. It is guaranteed that all records
+ * previous to the returned value have been finalized and are (or were)
+ * available to the reader.
*
* Context: Any context.
* Return: The sequence number of the next newest (not yet available) record
@@ -2016,34 +2260,19 @@
*/
u64 prb_next_seq(struct printk_ringbuffer *rb)
{
- struct prb_desc_ring *desc_ring = &rb->desc_ring;
- enum desc_state d_state;
- unsigned long id;
u64 seq;
- /* Check if the cached @id still points to a valid @seq. */
- id = atomic_long_read(&desc_ring->last_finalized_id);
- d_state = desc_read(desc_ring, id, NULL, &seq, NULL);
+ seq = desc_last_finalized_seq(rb);
- if (d_state == desc_finalized || d_state == desc_reusable) {
- /*
- * Begin searching after the last finalized record.
- *
- * On 0, the search must begin at 0 because of hack#2
- * of the bootstrapping phase it is not known if a
- * record at index 0 exists.
- */
- if (seq != 0)
- seq++;
- } else {
- /*
- * The information about the last finalized sequence number
- * has gone. It should happen only when there is a flood of
- * new messages and the ringbuffer is rapidly recycled.
- * Give up and start from the beginning.
- */
- seq = 0;
- }
+ /*
+ * Begin searching after the last finalized record.
+ *
+ * On 0, the search must begin at 0 because of hack#2
+ * of the bootstrapping phase it is not known if a
+ * record at index 0 exists.
+ */
+ if (seq != 0)
+ seq++;
/*
* The information about the last finalized @seq might be inaccurate.
@@ -2085,7 +2314,7 @@
rb->desc_ring.infos = infos;
atomic_long_set(&rb->desc_ring.head_id, DESC0_ID(descbits));
atomic_long_set(&rb->desc_ring.tail_id, DESC0_ID(descbits));
- atomic_long_set(&rb->desc_ring.last_finalized_id, DESC0_ID(descbits));
+ atomic_long_set(&rb->desc_ring.last_finalized_seq, 0);
rb->text_data_ring.size_bits = textbits;
rb->text_data_ring.data = text_buf;
diff --git a/kernel/printk/printk_ringbuffer.h b/kernel/printk/printk_ringbuffer.h
index 18cd25e..52626d0 100644
--- a/kernel/printk/printk_ringbuffer.h
+++ b/kernel/printk/printk_ringbuffer.h
@@ -75,7 +75,7 @@
struct printk_info *infos;
atomic_long_t head_id;
atomic_long_t tail_id;
- atomic_long_t last_finalized_id;
+ atomic_long_t last_finalized_seq;
};
/*
@@ -127,8 +127,22 @@
#define DESC_SV(id, state) (((unsigned long)state << DESC_FLAGS_SHIFT) | id)
#define DESC_ID_MASK (~DESC_FLAGS_MASK)
#define DESC_ID(sv) ((sv) & DESC_ID_MASK)
+
+/*
+ * Special data block logical position values (for fields of
+ * @prb_desc.text_blk_lpos).
+ *
+ * - Bit0 is used to identify if the record has no data block. (Implemented in
+ * the LPOS_DATALESS() macro.)
+ *
+ * - Bit1 specifies the reason for not having a data block.
+ *
+ * These special values could never be real lpos values because of the
+ * meta data and alignment padding of data blocks. (See to_blk_size() for
+ * details.)
+ */
#define FAILED_LPOS 0x1
-#define NO_LPOS 0x3
+#define EMPTY_LINE_LPOS 0x3
#define FAILED_BLK_LPOS \
{ \
@@ -259,7 +273,7 @@
.infos = &_##name##_infos[0], \
.head_id = ATOMIC_INIT(DESC0_ID(descbits)), \
.tail_id = ATOMIC_INIT(DESC0_ID(descbits)), \
- .last_finalized_id = ATOMIC_INIT(DESC0_ID(descbits)), \
+ .last_finalized_seq = ATOMIC_INIT(0), \
}, \
.text_data_ring = { \
.size_bits = (avgtextbits) + (descbits), \
@@ -378,7 +392,41 @@
bool prb_read_valid_info(struct printk_ringbuffer *rb, u64 seq,
struct printk_info *info, unsigned int *line_count);
+u64 prb_first_seq(struct printk_ringbuffer *rb);
u64 prb_first_valid_seq(struct printk_ringbuffer *rb);
u64 prb_next_seq(struct printk_ringbuffer *rb);
+u64 prb_next_reserve_seq(struct printk_ringbuffer *rb);
+
+#ifdef CONFIG_64BIT
+
+#define __u64seq_to_ulseq(u64seq) (u64seq)
+#define __ulseq_to_u64seq(rb, ulseq) (ulseq)
+
+#else /* CONFIG_64BIT */
+
+#define __u64seq_to_ulseq(u64seq) ((u32)u64seq)
+
+static inline u64 __ulseq_to_u64seq(struct printk_ringbuffer *rb, u32 ulseq)
+{
+ u64 rb_first_seq = prb_first_seq(rb);
+ u64 seq;
+
+ /*
+ * The provided sequence is only the lower 32 bits of the ringbuffer
+ * sequence. It needs to be expanded to 64bit. Get the first sequence
+ * number from the ringbuffer and fold it.
+ *
+ * Having a 32bit representation in the console is sufficient.
+ * If a console ever gets more than 2^31 records behind
+ * the ringbuffer then this is the least of the problems.
+ *
+ * Also the access to the ring buffer is always safe.
+ */
+ seq = rb_first_seq - (s32)((u32)rb_first_seq - ulseq);
+
+ return seq;
+}
+
+#endif /* CONFIG_64BIT */
#endif /* _KERNEL_PRINTK_RINGBUFFER_H */
diff --git a/lib/dump_stack.c b/lib/dump_stack.c
index 83471e8..222c6d6 100644
--- a/lib/dump_stack.c
+++ b/lib/dump_stack.c
@@ -96,15 +96,25 @@
*/
asmlinkage __visible void dump_stack_lvl(const char *log_lvl)
{
+ bool in_panic = this_cpu_in_panic();
unsigned long flags;
/*
* Permit this cpu to perform nested stack dumps while serialising
- * against other CPUs
+ * against other CPUs, unless this CPU is in panic.
+ *
+ * When in panic, non-panic CPUs are not permitted to store new
+ * printk messages so there is no need to synchronize the output.
+ * This avoids potential deadlock in panic() if another CPU is
+ * holding and unable to release the printk_cpu_sync.
*/
- printk_cpu_sync_get_irqsave(flags);
+ if (!in_panic)
+ printk_cpu_sync_get_irqsave(flags);
+
__dump_stack(log_lvl);
- printk_cpu_sync_put_irqrestore(flags);
+
+ if (!in_panic)
+ printk_cpu_sync_put_irqrestore(flags);
}
EXPORT_SYMBOL(dump_stack_lvl);
