kernel/locking/lockdep.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * kernel/lockdep.c
 *
 * Runtime locking correctness validator
 *
 * Started by Ingo Molnar:
 *
 *  Copyright (C) 2006,2007 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
 *  Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra
 *
 * this code maps all the lock dependencies as they occur in a live kernel
 * and will warn about the following classes of locking bugs:
 *
 * - lock inversion scenarios
 * - circular lock dependencies
 * - hardirq/softirq safe/unsafe locking bugs
 *
 * Bugs are reported even if the current locking scenario does not cause
 * any deadlock at this point.
 *
 * I.e. if anytime in the past two locks were taken in a different order,
 * even if it happened for another task, even if those were different
 * locks (but of the same class as this lock), this code will detect it.
 *
 * Thanks to Arjan van de Ven for coming up with the initial idea of
 * mapping lock dependencies runtime.
 */
#define DISABLE_BRANCH_PROFILING
#include <linux/mutex.h>
#include <linux/sched.h>
#include <linux/sched/clock.h>
#include <linux/sched/task.h>
#include <linux/sched/mm.h>
#include <linux/delay.h>
#include <linux/module.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/spinlock.h>
#include <linux/kallsyms.h>
#include <linux/interrupt.h>
#include <linux/stacktrace.h>
#include <linux/debug_locks.h>
#include <linux/irqflags.h>
#include <linux/utsname.h>
#include <linux/hash.h>
#include <linux/ftrace.h>
#include <linux/stringify.h>
#include <linux/bitmap.h>
#include <linux/bitops.h>
#include <linux/gfp.h>
#include <linux/random.h>
#include <linux/jhash.h>
#include <linux/nmi.h>
#include <linux/rcupdate.h>
#include <linux/kprobes.h>
#include <linux/lockdep.h>
#include <linux/context_tracking.h>

#include <asm/sections.h>

#include "lockdep_internals.h"

#include <trace/events/lock.h>

#ifdef CONFIG_PROVE_LOCKING
static int prove_locking = 1;
module_param(prove_locking, int, 0644);
#else
#define prove_locking 0
#endif

#ifdef CONFIG_LOCK_STAT
static int lock_stat = 1;
module_param(lock_stat, int, 0644);
#else
#define lock_stat 0
#endif

#ifdef CONFIG_SYSCTL
static struct ctl_table kern_lockdep_table[] = {
#ifdef CONFIG_PROVE_LOCKING
	{
		.procname       = "prove_locking",
		.data           = &prove_locking,
		.maxlen         = sizeof(int),
		.mode           = 0644,
		.proc_handler   = proc_dointvec,
	},
#endif /* CONFIG_PROVE_LOCKING */
#ifdef CONFIG_LOCK_STAT
	{
		.procname       = "lock_stat",
		.data           = &lock_stat,
		.maxlen         = sizeof(int),
		.mode           = 0644,
		.proc_handler   = proc_dointvec,
	},
#endif /* CONFIG_LOCK_STAT */
};

static __init int kernel_lockdep_sysctls_init(void)
{
	register_sysctl_init("kernel", kern_lockdep_table);
	return 0;
}
late_initcall(kernel_lockdep_sysctls_init);
#endif /* CONFIG_SYSCTL */

DEFINE_PER_CPU(unsigned int, lockdep_recursion);
EXPORT_PER_CPU_SYMBOL_GPL(lockdep_recursion);

static __always_inline bool lockdep_enabled(void)
{
	if (!debug_locks)
		return false;

	if (this_cpu_read(lockdep_recursion))
		return false;

	if (current->lockdep_recursion)
		return false;

	return true;
}

/*
 * lockdep_lock: protects the lockdep graph, the hashes and the
 *               class/list/hash allocators.
 *
 * This is one of the rare exceptions where it's justified
 * to use a raw spinlock - we really dont want the spinlock
 * code to recurse back into the lockdep code...
 */
static arch_spinlock_t __lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
static struct task_struct *__owner;

static inline void lockdep_lock(void)
{
	DEBUG_LOCKS_WARN_ON(!irqs_disabled());

	__this_cpu_inc(lockdep_recursion);
	arch_spin_lock(&__lock);
	__owner = current;
}

static inline void lockdep_unlock(void)
{
	DEBUG_LOCKS_WARN_ON(!irqs_disabled());

	if (debug_locks && DEBUG_LOCKS_WARN_ON(__owner != current))
		return;

	__owner = NULL;
	arch_spin_unlock(&__lock);
	__this_cpu_dec(lockdep_recursion);
}

static inline bool lockdep_assert_locked(void)
{
	return DEBUG_LOCKS_WARN_ON(__owner != current);
}

static struct task_struct *lockdep_selftest_task_struct;


static int graph_lock(void)
{
	lockdep_lock();
	/*
	 * Make sure that if another CPU detected a bug while
	 * walking the graph we dont change it (while the other
	 * CPU is busy printing out stuff with the graph lock
	 * dropped already)
	 */
	if (!debug_locks) {
		lockdep_unlock();
		return 0;
	}
	return 1;
}

static inline void graph_unlock(void)
{
	lockdep_unlock();
}

/*
 * Turn lock debugging off and return with 0 if it was off already,
 * and also release the graph lock:
 */
static inline int debug_locks_off_graph_unlock(void)
{
	int ret = debug_locks_off();

	lockdep_unlock();

	return ret;
}

unsigned long nr_list_entries;
static struct lock_list list_entries[MAX_LOCKDEP_ENTRIES];
static DECLARE_BITMAP(list_entries_in_use, MAX_LOCKDEP_ENTRIES);

/*
 * All data structures here are protected by the global debug_lock.
 *
 * nr_lock_classes is the number of elements of lock_classes[] that is
 * in use.
 */
#define KEYHASH_BITS		(MAX_LOCKDEP_KEYS_BITS - 1)
#define KEYHASH_SIZE		(1UL << KEYHASH_BITS)
static struct hlist_head lock_keys_hash[KEYHASH_SIZE];
unsigned long nr_lock_classes;
unsigned long nr_zapped_classes;
unsigned long max_lock_class_idx;
struct lock_class lock_classes[MAX_LOCKDEP_KEYS];
DECLARE_BITMAP(lock_classes_in_use, MAX_LOCKDEP_KEYS);

static inline struct lock_class *hlock_class(struct held_lock *hlock)
{
	unsigned int class_idx = hlock->class_idx;

	/* Don't re-read hlock->class_idx, can't use READ_ONCE() on bitfield */
	barrier();

	if (!test_bit(class_idx, lock_classes_in_use)) {
		/*
		 * Someone passed in garbage, we give up.
		 */
		DEBUG_LOCKS_WARN_ON(1);
		return NULL;
	}

	/*
	 * At this point, if the passed hlock->class_idx is still garbage,
	 * we just have to live with it
	 */
	return lock_classes + class_idx;
}

#ifdef CONFIG_LOCK_STAT
static DEFINE_PER_CPU(struct lock_class_stats[MAX_LOCKDEP_KEYS], cpu_lock_stats);

static inline u64 lockstat_clock(void)
{
	return local_clock();
}

static int lock_point(unsigned long points[], unsigned long ip)
{
	int i;

	for (i = 0; i < LOCKSTAT_POINTS; i++) {
		if (points[i] == 0) {
			points[i] = ip;
			break;
		}
		if (points[i] == ip)
			break;
	}

	return i;
}

static void lock_time_inc(struct lock_time *lt, u64 time)
{
	if (time > lt->max)
		lt->max = time;

	if (time < lt->min || !lt->nr)
		lt->min = time;

	lt->total += time;
	lt->nr++;
}

static inline void lock_time_add(struct lock_time *src, struct lock_time *dst)
{
	if (!src->nr)
		return;

	if (src->max > dst->max)
		dst->max = src->max;

	if (src->min < dst->min || !dst->nr)
		dst->min = src->min;

	dst->total += src->total;
	dst->nr += src->nr;
}

struct lock_class_stats lock_stats(struct lock_class *class)
{
	struct lock_class_stats stats;
	int cpu, i;

	memset(&stats, 0, sizeof(struct lock_class_stats));
	for_each_possible_cpu(cpu) {
		struct lock_class_stats *pcs =
			&per_cpu(cpu_lock_stats, cpu)[class - lock_classes];

		for (i = 0; i < ARRAY_SIZE(stats.contention_point); i++)
			stats.contention_point[i] += pcs->contention_point[i];

		for (i = 0; i < ARRAY_SIZE(stats.contending_point); i++)
			stats.contending_point[i] += pcs->contending_point[i];

		lock_time_add(&pcs->read_waittime, &stats.read_waittime);
		lock_time_add(&pcs->write_waittime, &stats.write_waittime);

		lock_time_add(&pcs->read_holdtime, &stats.read_holdtime);
		lock_time_add(&pcs->write_holdtime, &stats.write_holdtime);

		for (i = 0; i < ARRAY_SIZE(stats.bounces); i++)
			stats.bounces[i] += pcs->bounces[i];
	}

	return stats;
}

void clear_lock_stats(struct lock_class *class)
{
	int cpu;

	for_each_possible_cpu(cpu) {
		struct lock_class_stats *cpu_stats =
			&per_cpu(cpu_lock_stats, cpu)[class - lock_classes];

		memset(cpu_stats, 0, sizeof(struct lock_class_stats));
	}
	memset(class->contention_point, 0, sizeof(class->contention_point));
	memset(class->contending_point, 0, sizeof(class->contending_point));
}

static struct lock_class_stats *get_lock_stats(struct lock_class *class)
{
	return &this_cpu_ptr(cpu_lock_stats)[class - lock_classes];
}

static void lock_release_holdtime(struct held_lock *hlock)
{
	struct lock_class_stats *stats;
	u64 holdtime;

	if (!lock_stat)
		return;

	holdtime = lockstat_clock() - hlock->holdtime_stamp;

	stats = get_lock_stats(hlock_class(hlock));
	if (hlock->read)
		lock_time_inc(&stats->read_holdtime, holdtime);
	else
		lock_time_inc(&stats->write_holdtime, holdtime);
}
#else
static inline void lock_release_holdtime(struct held_lock *hlock)
{
}
#endif

/*
 * We keep a global list of all lock classes. The list is only accessed with
 * the lockdep spinlock lock held. free_lock_classes is a list with free
 * elements. These elements are linked together by the lock_entry member in
 * struct lock_class.
 */
static LIST_HEAD(all_lock_classes);
static LIST_HEAD(free_lock_classes);

/**
 * struct pending_free - information about data structures about to be freed
 * @zapped: Head of a list with struct lock_class elements.
 * @lock_chains_being_freed: Bitmap that indicates which lock_chains[] elements
 *	are about to be freed.
 */
struct pending_free {
	struct list_head zapped;
	DECLARE_BITMAP(lock_chains_being_freed, MAX_LOCKDEP_CHAINS);
};

/**
 * struct delayed_free - data structures used for delayed freeing
 *
 * A data structure for delayed freeing of data structures that may be
 * accessed by RCU readers at the time these were freed.
 *
 * @rcu_head:  Used to schedule an RCU callback for freeing data structures.
 * @index:     Index of @pf to which freed data structures are added.
 * @scheduled: Whether or not an RCU callback has been scheduled.
 * @pf:        Array with information about data structures about to be freed.
 */
static struct delayed_free {
	struct rcu_head		rcu_head;
	int			index;
	int			scheduled;
	struct pending_free	pf[2];
} delayed_free;

/*
 * The lockdep classes are in a hash-table as well, for fast lookup:
 */
#define CLASSHASH_BITS		(MAX_LOCKDEP_KEYS_BITS - 1)
#define CLASSHASH_SIZE		(1UL << CLASSHASH_BITS)
#define __classhashfn(key)	hash_long((unsigned long)key, CLASSHASH_BITS)
#define classhashentry(key)	(classhash_table + __classhashfn((key)))

static struct hlist_head classhash_table[CLASSHASH_SIZE];

/*
 * We put the lock dependency chains into a hash-table as well, to cache
 * their existence:
 */
#define CHAINHASH_BITS		(MAX_LOCKDEP_CHAINS_BITS-1)
#define CHAINHASH_SIZE		(1UL << CHAINHASH_BITS)
#define __chainhashfn(chain)	hash_long(chain, CHAINHASH_BITS)
#define chainhashentry(chain)	(chainhash_table + __chainhashfn((chain)))

static struct hlist_head chainhash_table[CHAINHASH_SIZE];

/*
 * the id of held_lock
 */
static inline u16 hlock_id(struct held_lock *hlock)
{
	BUILD_BUG_ON(MAX_LOCKDEP_KEYS_BITS + 2 > 16);

	return (hlock->class_idx | (hlock->read << MAX_LOCKDEP_KEYS_BITS));
}

static inline unsigned int chain_hlock_class_idx(u16 hlock_id)
{
	return hlock_id & (MAX_LOCKDEP_KEYS - 1);
}

/*
 * The hash key of the lock dependency chains is a hash itself too:
 * it's a hash of all locks taken up to that lock, including that lock.
 * It's a 64-bit hash, because it's important for the keys to be
 * unique.
 */
static inline u64 iterate_chain_key(u64 key, u32 idx)
{
	u32 k0 = key, k1 = key >> 32;

	__jhash_mix(idx, k0, k1); /* Macro that modifies arguments! */

	return k0 | (u64)k1 << 32;
}

void lockdep_init_task(struct task_struct *task)
{
	task->lockdep_depth = 0; /* no locks held yet */
	task->curr_chain_key = INITIAL_CHAIN_KEY;
	task->lockdep_recursion = 0;
}

static __always_inline void lockdep_recursion_inc(void)
{
	__this_cpu_inc(lockdep_recursion);
}

static __always_inline void lockdep_recursion_finish(void)
{
	if (WARN_ON_ONCE(__this_cpu_dec_return(lockdep_recursion)))
		__this_cpu_write(lockdep_recursion, 0);
}

void lockdep_set_selftest_task(struct task_struct *task)
{
	lockdep_selftest_task_struct = task;
}

/*
 * Debugging switches:
 */

#define VERBOSE			0
#define VERY_VERBOSE		0

#if VERBOSE
# define HARDIRQ_VERBOSE	1
# define SOFTIRQ_VERBOSE	1
#else
# define HARDIRQ_VERBOSE	0
# define SOFTIRQ_VERBOSE	0
#endif

#if VERBOSE || HARDIRQ_VERBOSE || SOFTIRQ_VERBOSE
/*
 * Quick filtering for interesting events:
 */
static int class_filter(struct lock_class *class)
{
#if 0
	/* Example */
	if (class->name_version == 1 &&
			!strcmp(class->name, "lockname"))
		return 1;
	if (class->name_version == 1 &&
			!strcmp(class->name, "&struct->lockfield"))
		return 1;
#endif
	/* Filter everything else. 1 would be to allow everything else */
	return 0;
}
#endif

static int verbose(struct lock_class *class)
{
#if VERBOSE
	return class_filter(class);
#endif
	return 0;
}

static void print_lockdep_off(const char *bug_msg)
{
	printk(KERN_DEBUG "%s\n", bug_msg);
	printk(KERN_DEBUG "turning off the locking correctness validator.\n");
#ifdef CONFIG_LOCK_STAT
	printk(KERN_DEBUG "Please attach the output of /proc/lock_stat to the bug report\n");
#endif
}

unsigned long nr_stack_trace_entries;

#ifdef CONFIG_PROVE_LOCKING
/**
 * struct lock_trace - single stack backtrace
 * @hash_entry:	Entry in a stack_trace_hash[] list.
 * @hash:	jhash() of @entries.
 * @nr_entries:	Number of entries in @entries.
 * @entries:	Actual stack backtrace.
 */
struct lock_trace {
	struct hlist_node	hash_entry;
	u32			hash;
	u32			nr_entries;
	unsigned long		entries[] __aligned(sizeof(unsigned long));
};
#define LOCK_TRACE_SIZE_IN_LONGS				\
	(sizeof(struct lock_trace) / sizeof(unsigned long))
/*
 * Stack-trace: sequence of lock_trace structures. Protected by the graph_lock.
 */
static unsigned long stack_trace[MAX_STACK_TRACE_ENTRIES];
static struct hlist_head stack_trace_hash[STACK_TRACE_HASH_SIZE];

static bool traces_identical(struct lock_trace *t1, struct lock_trace *t2)
{
	return t1->hash == t2->hash && t1->nr_entries == t2->nr_entries &&
		memcmp(t1->entries, t2->entries,
		       t1->nr_entries * sizeof(t1->entries[0])) == 0;
}

static struct lock_trace *save_trace(void)
{
	struct lock_trace *trace, *t2;
	struct hlist_head *hash_head;
	u32 hash;
	int max_entries;

	BUILD_BUG_ON_NOT_POWER_OF_2(STACK_TRACE_HASH_SIZE);
	BUILD_BUG_ON(LOCK_TRACE_SIZE_IN_LONGS >= MAX_STACK_TRACE_ENTRIES);

	trace = (struct lock_trace *)(stack_trace + nr_stack_trace_entries);
	max_entries = MAX_STACK_TRACE_ENTRIES - nr_stack_trace_entries -
		LOCK_TRACE_SIZE_IN_LONGS;

	if (max_entries <= 0) {
		if (!debug_locks_off_graph_unlock())
			return NULL;

		print_lockdep_off("BUG: MAX_STACK_TRACE_ENTRIES too low!");
		dump_stack();

		return NULL;
	}
	trace->nr_entries = stack_trace_save(trace->entries, max_entries, 3);

	hash = jhash(trace->entries, trace->nr_entries *
		     sizeof(trace->entries[0]), 0);
	trace->hash = hash;
	hash_head = stack_trace_hash + (hash & (STACK_TRACE_HASH_SIZE - 1));
	hlist_for_each_entry(t2, hash_head, hash_entry) {
		if (traces_identical(trace, t2))
			return t2;
	}
	nr_stack_trace_entries += LOCK_TRACE_SIZE_IN_LONGS + trace->nr_entries;
	hlist_add_head(&trace->hash_entry, hash_head);

	return trace;
}

/* Return the number of stack traces in the stack_trace[] array. */
u64 lockdep_stack_trace_count(void)
{
	struct lock_trace *trace;
	u64 c = 0;
	int i;

	for (i = 0; i < ARRAY_SIZE(stack_trace_hash); i++) {
		hlist_for_each_entry(trace, &stack_trace_hash[i], hash_entry) {
			c++;
		}
	}

	return c;
}

/* Return the number of stack hash chains that have at least one stack trace. */
u64 lockdep_stack_hash_count(void)
{
	u64 c = 0;
	int i;

	for (i = 0; i < ARRAY_SIZE(stack_trace_hash); i++)
		if (!hlist_empty(&stack_trace_hash[i]))
			c++;

	return c;
}
#endif

unsigned int nr_hardirq_chains;
unsigned int nr_softirq_chains;
unsigned int nr_process_chains;
unsigned int max_lockdep_depth;

#ifdef CONFIG_DEBUG_LOCKDEP
/*
 * Various lockdep statistics:
 */
DEFINE_PER_CPU(struct lockdep_stats, lockdep_stats);
#endif

#ifdef CONFIG_PROVE_LOCKING
/*
 * Locking printouts:
 */

#define __USAGE(__STATE)						\
	[LOCK_USED_IN_##__STATE] = "IN-"__stringify(__STATE)"-W",	\
	[LOCK_ENABLED_##__STATE] = __stringify(__STATE)"-ON-W",		\
	[LOCK_USED_IN_##__STATE##_READ] = "IN-"__stringify(__STATE)"-R",\
	[LOCK_ENABLED_##__STATE##_READ] = __stringify(__STATE)"-ON-R",

static const char *usage_str[] =
{
#define LOCKDEP_STATE(__STATE) __USAGE(__STATE)
#include "lockdep_states.h"
#undef LOCKDEP_STATE
	[LOCK_USED] = "INITIAL USE",
	[LOCK_USED_READ] = "INITIAL READ USE",
	/* abused as string storage for verify_lock_unused() */
	[LOCK_USAGE_STATES] = "IN-NMI",
};
#endif

const char *__get_key_name(const struct lockdep_subclass_key *key, char *str)
{
	return kallsyms_lookup((unsigned long)key, NULL, NULL, NULL, str);
}

static inline unsigned long lock_flag(enum lock_usage_bit bit)
{
	return 1UL << bit;
}

static char get_usage_char(struct lock_class *class, enum lock_usage_bit bit)
{
	/*
	 * The usage character defaults to '.' (i.e., irqs disabled and not in
	 * irq context), which is the safest usage category.
	 */
	char c = '.';

	/*
	 * The order of the following usage checks matters, which will
	 * result in the outcome character as follows:
	 *
	 * - '+': irq is enabled and not in irq context
	 * - '-': in irq context and irq is disabled
	 * - '?': in irq context and irq is enabled
	 */
	if (class->usage_mask & lock_flag(bit + LOCK_USAGE_DIR_MASK)) {
		c = '+';
		if (class->usage_mask & lock_flag(bit))
			c = '?';
	} else if (class->usage_mask & lock_flag(bit))
		c = '-';

	return c;
}

void get_usage_chars(struct lock_class *class, char usage[LOCK_USAGE_CHARS])
{
	int i = 0;

#define LOCKDEP_STATE(__STATE) 						\
	usage[i++] = get_usage_char(class, LOCK_USED_IN_##__STATE);	\
	usage[i++] = get_usage_char(class, LOCK_USED_IN_##__STATE##_READ);
#include "lockdep_states.h"
#undef LOCKDEP_STATE

	usage[i] = '\0';
}

static void __print_lock_name(struct held_lock *hlock, struct lock_class *class)
{
	char str[KSYM_NAME_LEN];
	const char *name;

	name = class->name;
	if (!name) {
		name = __get_key_name(class->key, str);
		printk(KERN_CONT "%s", name);
	} else {
		printk(KERN_CONT "%s", name);
		if (class->name_version > 1)
			printk(KERN_CONT "#%d", class->name_version);
		if (class->subclass)
			printk(KERN_CONT "/%d", class->subclass);
		if (hlock && class->print_fn)
			class->print_fn(hlock->instance);
	}
}

static void print_lock_name(struct held_lock *hlock, struct lock_class *class)
{
	char usage[LOCK_USAGE_CHARS];

	get_usage_chars(class, usage);

	printk(KERN_CONT " (");
	__print_lock_name(hlock, class);
	printk(KERN_CONT "){%s}-{%d:%d}", usage,
			class->wait_type_outer ?: class->wait_type_inner,
			class->wait_type_inner);
}

static void print_lockdep_cache(struct lockdep_map *lock)
{
	const char *name;
	char str[KSYM_NAME_LEN];

	name = lock->name;
	if (!name)
		name = __get_key_name(lock->key->subkeys, str);

	printk(KERN_CONT "%s", name);
}

static void print_lock(struct held_lock *hlock)
{
	/*
	 * We can be called locklessly through debug_show_all_locks() so be
	 * extra careful, the hlock might have been released and cleared.
	 *
	 * If this indeed happens, lets pretend it does not hurt to continue
	 * to print the lock unless the hlock class_idx does not point to a
	 * registered class. The rationale here is: since we don't attempt
	 * to distinguish whether we are in this situation, if it just
	 * happened we can't count on class_idx to tell either.
	 */
	struct lock_class *lock = hlock_class(hlock);

	if (!lock) {
		printk(KERN_CONT "<RELEASED>\n");
		return;
	}

	printk(KERN_CONT "%px", hlock->instance);
	print_lock_name(hlock, lock);
	printk(KERN_CONT ", at: %pS\n", (void *)hlock->acquire_ip);
}

static void lockdep_print_held_locks(struct task_struct *p)
{
	int i, depth = READ_ONCE(p->lockdep_depth);

	if (!depth)
		printk("no locks held by %s/%d.\n", p->comm, task_pid_nr(p));
	else
		printk("%d lock%s held by %s/%d:\n", depth,
		       depth > 1 ? "s" : "", p->comm, task_pid_nr(p));
	/*
	 * It's not reliable to print a task's held locks if it's not sleeping
	 * and it's not the current task.
	 */
	if (p != current && task_is_running(p))
		return;
	for (i = 0; i < depth; i++) {
		printk(" #%d: ", i);
		print_lock(p->held_locks + i);
	}
}

static void print_kernel_ident(void)
{
	printk("%s %.*s %s\n", init_utsname()->release,
		(int)strcspn(init_utsname()->version, " "),
		init_utsname()->version,
		print_tainted());
}

static int very_verbose(struct lock_class *class)
{
#if VERY_VERBOSE
	return class_filter(class);
#endif
	return 0;
}

/*
 * Is this the address of a static object:
 */
#ifdef __KERNEL__
static int static_obj(const void *obj)
{
	unsigned long addr = (unsigned long) obj;

	if (is_kernel_core_data(addr))
		return 1;

	/*
	 * keys are allowed in the __ro_after_init section.
	 */
	if (is_kernel_rodata(addr))
		return 1;

	/*
	 * in initdata section and used during bootup only?
	 * NOTE: On some platforms the initdata section is
	 * outside of the _stext ... _end range.
	 */
	if (system_state < SYSTEM_FREEING_INITMEM &&
		init_section_contains((void *)addr, 1))
		return 1;

	/*
	 * in-kernel percpu var?
	 */
	if (is_kernel_percpu_address(addr))
		return 1;

	/*
	 * module static or percpu var?
	 */
	return is_module_address(addr) || is_module_percpu_address(addr);
}
#endif

/*
 * To make lock name printouts unique, we calculate a unique
 * class->name_version generation counter. The caller must hold the graph
 * lock.
 */
static int count_matching_names(struct lock_class *new_class)
{
	struct lock_class *class;
	int count = 0;

	if (!new_class->name)
		return 0;

	list_for_each_entry(class, &all_lock_classes, lock_entry) {
		if (new_class->key - new_class->subclass == class->key)
			return class->name_version;
		if (class->name && !strcmp(class->name, new_class->name))
			count = max(count, class->name_version);
	}

	return count + 1;
}

/* used from NMI context -- must be lockless */
static noinstr struct lock_class *
look_up_lock_class(const struct lockdep_map *lock, unsigned int subclass)
{
	struct lockdep_subclass_key *key;
	struct hlist_head *hash_head;
	struct lock_class *class;

	if (unlikely(subclass >= MAX_LOCKDEP_SUBCLASSES)) {
		instrumentation_begin();
		debug_locks_off();
		printk(KERN_ERR
			"BUG: looking up invalid subclass: %u\n", subclass);
		printk(KERN_ERR
			"turning off the locking correctness validator.\n");
		dump_stack();
		instrumentation_end();
		return NULL;
	}

	/*
	 * If it is not initialised then it has never been locked,
	 * so it won't be present in the hash table.
	 */
	if (unlikely(!lock->key))
		return NULL;

	/*
	 * NOTE: the class-key must be unique. For dynamic locks, a static
	 * lock_class_key variable is passed in through the mutex_init()
	 * (or spin_lock_init()) call - which acts as the key. For static
	 * locks we use the lock object itself as the key.
	 */
	BUILD_BUG_ON(sizeof(struct lock_class_key) >
			sizeof(struct lockdep_map));

	key = lock->key->subkeys + subclass;

	hash_head = classhashentry(key);

	/*
	 * We do an RCU walk of the hash, see lockdep_free_key_range().
	 */
	if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
		return NULL;

	hlist_for_each_entry_rcu_notrace(class, hash_head, hash_entry) {
		if (class->key == key) {
			/*
			 * Huh! same key, different name? Did someone trample
			 * on some memory? We're most confused.
			 */
			WARN_ONCE(class->name != lock->name &&
				  lock->key != &__lockdep_no_validate__,
				  "Looking for class \"%s\" with key %ps, but found a different class \"%s\" with the same key\n",
				  lock->name, lock->key, class->name);
			return class;
		}
	}

	return NULL;
}

/*
 * Static locks do not have their class-keys yet - for them the key is
 * the lock object itself. If the lock is in the per cpu area, the
 * canonical address of the lock (per cpu offset removed) is used.
 */
static bool assign_lock_key(struct lockdep_map *lock)
{
	unsigned long can_addr, addr = (unsigned long)lock;

#ifdef __KERNEL__
	/*
	 * lockdep_free_key_range() assumes that struct lock_class_key
	 * objects do not overlap. Since we use the address of lock
	 * objects as class key for static objects, check whether the
	 * size of lock_class_key objects does not exceed the size of
	 * the smallest lock object.
	 */
	BUILD_BUG_ON(sizeof(struct lock_class_key) > sizeof(raw_spinlock_t));
#endif

	if (__is_kernel_percpu_address(addr, &can_addr))
		lock->key = (void *)can_addr;
	else if (__is_module_percpu_address(addr, &can_addr))
		lock->key = (void *)can_addr;
	else if (static_obj(lock))
		lock->key = (void *)lock;
	else {
		/* Debug-check: all keys must be persistent! */
		debug_locks_off();
		pr_err("INFO: trying to register non-static key.\n");
		pr_err("The code is fine but needs lockdep annotation, or maybe\n");
		pr_err("you didn't initialize this object before use?\n");
		pr_err("turning off the locking correctness validator.\n");
		dump_stack();
		return false;
	}

	return true;
}

#ifdef CONFIG_DEBUG_LOCKDEP

/* Check whether element @e occurs in list @h */
static bool in_list(struct list_head *e, struct list_head *h)
{
	struct list_head *f;

	list_for_each(f, h) {
		if (e == f)
			return true;
	}

	return false;
}

/*
 * Check whether entry @e occurs in any of the locks_after or locks_before
 * lists.
 */
static bool in_any_class_list(struct list_head *e)
{
	struct lock_class *class;
	int i;

	for (i = 0; i < ARRAY_SIZE(lock_classes); i++) {
		class = &lock_classes[i];
		if (in_list(e, &class->locks_after) ||
		    in_list(e, &class->locks_before))
			return true;
	}
	return false;
}

static bool class_lock_list_valid(struct lock_class *c, struct list_head *h)
{
	struct lock_list *e;

	list_for_each_entry(e, h, entry) {
		if (e->links_to != c) {
			printk(KERN_INFO "class %s: mismatch for lock entry %ld; class %s <> %s",
			       c->name ? : "(?)",
			       (unsigned long)(e - list_entries),
			       e->links_to && e->links_to->name ?
			       e->links_to->name : "(?)",
			       e->class && e->class->name ? e->class->name :
			       "(?)");
			return false;
		}
	}
	return true;
}

#ifdef CONFIG_PROVE_LOCKING
static u16 chain_hlocks[MAX_LOCKDEP_CHAIN_HLOCKS];
#endif

static bool check_lock_chain_key(struct lock_chain *chain)
{
#ifdef CONFIG_PROVE_LOCKING
	u64 chain_key = INITIAL_CHAIN_KEY;
	int i;

	for (i = chain->base; i < chain->base + chain->depth; i++)
		chain_key = iterate_chain_key(chain_key, chain_hlocks[i]);
	/*
	 * The 'unsigned long long' casts avoid that a compiler warning
	 * is reported when building tools/lib/lockdep.
	 */
	if (chain->chain_key != chain_key) {
		printk(KERN_INFO "chain %lld: key %#llx <> %#llx\n",
		       (unsigned long long)(chain - lock_chains),
		       (unsigned long long)chain->chain_key,
		       (unsigned long long)chain_key);
		return false;
	}
#endif
	return true;
}

static bool in_any_zapped_class_list(struct lock_class *class)
{
	struct pending_free *pf;
	int i;

	for (i = 0, pf = delayed_free.pf; i < ARRAY_SIZE(delayed_free.pf); i++, pf++) {
		if (in_list(&class->lock_entry, &pf->zapped))
			return true;
	}

	return false;
}

static bool __check_data_structures(void)
{
	struct lock_class *class;
	struct lock_chain *chain;
	struct hlist_head *head;
	struct lock_list *e;
	int i;

	/* Check whether all classes occur in a lock list. */
	for (i = 0; i < ARRAY_SIZE(lock_classes); i++) {
		class = &lock_classes[i];
		if (!in_list(&class->lock_entry, &all_lock_classes) &&
		    !in_list(&class->lock_entry, &free_lock_classes) &&
		    !in_any_zapped_class_list(class)) {
			printk(KERN_INFO "class %px/%s is not in any class list\n",
			       class, class->name ? : "(?)");
			return false;
		}
	}

	/* Check whether all classes have valid lock lists. */
	for (i = 0; i < ARRAY_SIZE(lock_classes); i++) {
		class = &lock_classes[i];
		if (!class_lock_list_valid(class, &class->locks_before))
			return false;
		if (!class_lock_list_valid(class, &class->locks_after))
			return false;
	}

	/* Check the chain_key of all lock chains. */
	for (i = 0; i < ARRAY_SIZE(chainhash_table); i++) {
		head = chainhash_table + i;
		hlist_for_each_entry_rcu(chain, head, entry) {
			if (!check_lock_chain_key(chain))
				return false;
		}
	}

	/*
	 * Check whether all list entries that are in use occur in a class
	 * lock list.
	 */
	for_each_set_bit(i, list_entries_in_use, ARRAY_SIZE(list_entries)) {
		e = list_entries + i;
		if (!in_any_class_list(&e->entry)) {
			printk(KERN_INFO "list entry %d is not in any class list; class %s <> %s\n",
			       (unsigned int)(e - list_entries),
			       e->class->name ? : "(?)",
			       e->links_to->name ? : "(?)");
			return false;
		}
	}

	/*
	 * Check whether all list entries that are not in use do not occur in
	 * a class lock list.
	 */
	for_each_clear_bit(i, list_entries_in_use, ARRAY_SIZE(list_entries)) {
		e = list_entries + i;
		if (in_any_class_list(&e->entry)) {
			printk(KERN_INFO "list entry %d occurs in a class list; class %s <> %s\n",
			       (unsigned int)(e - list_entries),
			       e->class && e->class->name ? e->class->name :
			       "(?)",
			       e->links_to && e->links_to->name ?
			       e->links_to->name : "(?)");
			return false;
		}
	}

	return true;
}

int check_consistency = 0;
module_param(check_consistency, int, 0644);

static void check_data_structures(void)
{
	static bool once = false;

	if (check_consistency && !once) {
		if (!__check_data_structures()) {
			once = true;
			WARN_ON(once);
		}
	}
}

#else /* CONFIG_DEBUG_LOCKDEP */

static inline void check_data_structures(void) { }

#endif /* CONFIG_DEBUG_LOCKDEP */

static void init_chain_block_buckets(void);

/*
 * Initialize the lock_classes[] array elements, the free_lock_classes list
 * and also the delayed_free structure.
 */
static void init_data_structures_once(void)
{
	static bool __read_mostly ds_initialized, rcu_head_initialized;
	int i;

	if (likely(rcu_head_initialized))
		return;

	if (system_state >= SYSTEM_SCHEDULING) {
		init_rcu_head(&delayed_free.rcu_head);
		rcu_head_initialized = true;
	}

	if (ds_initialized)
		return;

	ds_initialized = true;

	INIT_LIST_HEAD(&delayed_free.pf[0].zapped);
	INIT_LIST_HEAD(&delayed_free.pf[1].zapped);

	for (i = 0; i < ARRAY_SIZE(lock_classes); i++) {
		list_add_tail(&lock_classes[i].lock_entry, &free_lock_classes);
		INIT_LIST_HEAD(&lock_classes[i].locks_after);
		INIT_LIST_HEAD(&lock_classes[i].locks_before);
	}
	init_chain_block_buckets();
}

static inline struct hlist_head *keyhashentry(const struct lock_class_key *key)
{
	unsigned long hash = hash_long((uintptr_t)key, KEYHASH_BITS);

	return lock_keys_hash + hash;
}

/* Register a dynamically allocated key. */
void lockdep_register_key(struct lock_class_key *key)
{
	struct hlist_head *hash_head;
	struct lock_class_key *k;
	unsigned long flags;

	if (WARN_ON_ONCE(static_obj(key)))
		return;
	hash_head = keyhashentry(key);

	raw_local_irq_save(flags);
	if (!graph_lock())
		goto restore_irqs;
	hlist_for_each_entry_rcu(k, hash_head, hash_entry) {
		if (WARN_ON_ONCE(k == key))
			goto out_unlock;
	}
	hlist_add_head_rcu(&key->hash_entry, hash_head);
out_unlock:
	graph_unlock();
restore_irqs:
	raw_local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(lockdep_register_key);

/* Check whether a key has been registered as a dynamic key. */
static bool is_dynamic_key(const struct lock_class_key *key)
{
	struct hlist_head *hash_head;
	struct lock_class_key *k;
	bool found = false;

	if (WARN_ON_ONCE(static_obj(key)))
		return false;

	/*
	 * If lock debugging is disabled lock_keys_hash[] may contain
	 * pointers to memory that has already been freed. Avoid triggering
	 * a use-after-free in that case by returning early.
	 */
	if (!debug_locks)
		return true;

	hash_head = keyhashentry(key);

	rcu_read_lock();
	hlist_for_each_entry_rcu(k, hash_head, hash_entry) {
		if (k == key) {
			found = true;
			break;
		}
	}
	rcu_read_unlock();

	return found;
}

/*
 * Register a lock's class in the hash-table, if the class is not present
 * yet. Otherwise we look it up. We cache the result in the lock object
 * itself, so actual lookup of the hash should be once per lock object.
 */
static struct lock_class *
register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force)
{
	struct lockdep_subclass_key *key;
	struct hlist_head *hash_head;
	struct lock_class *class;
	int idx;

	DEBUG_LOCKS_WARN_ON(!irqs_disabled());

	class = look_up_lock_class(lock, subclass);
	if (likely(class))
		goto out_set_class_cache;

	if (!lock->key) {
		if (!assign_lock_key(lock))
			return NULL;
	} else if (!static_obj(lock->key) && !is_dynamic_key(lock->key)) {
		return NULL;
	}

	key = lock->key->subkeys + subclass;
	hash_head = classhashentry(key);

	if (!graph_lock()) {
		return NULL;
	}
	/*
	 * We have to do the hash-walk again, to avoid races
	 * with another CPU:
	 */
	hlist_for_each_entry_rcu(class, hash_head, hash_entry) {
		if (class->key == key)
			goto out_unlock_set;
	}

	init_data_structures_once();

	/* Allocate a new lock class and add it to the hash. */
	class = list_first_entry_or_null(&free_lock_classes, typeof(*class),
					 lock_entry);
	if (!class) {
		if (!debug_locks_off_graph_unlock()) {
			return NULL;
		}

		print_lockdep_off("BUG: MAX_LOCKDEP_KEYS too low!");
		dump_stack();
		return NULL;
	}
	nr_lock_classes++;
	__set_bit(class - lock_classes, lock_classes_in_use);
	debug_atomic_inc(nr_unused_locks);
	class->key = key;
	class->name = lock->name;
	class->subclass = subclass;
	WARN_ON_ONCE(!list_empty(&class->locks_before));
	WARN_ON_ONCE(!list_empty(&class->locks_after));
	class->name_version = count_matching_names(class);
	class->wait_type_inner = lock->wait_type_inner;
	class->wait_type_outer = lock->wait_type_outer;
	class->lock_type = lock->lock_type;
	/*
	 * We use RCU's safe list-add method to make
	 * parallel walking of the hash-list safe:
	 */
	hlist_add_head_rcu(&class->hash_entry, hash_head);
	/*
	 * Remove the class from the free list and add it to the global list
	 * of classes.
	 */
	list_move_tail(&class->lock_entry, &all_lock_classes);
	idx = class - lock_classes;
	if (idx > max_lock_class_idx)
		max_lock_class_idx = idx;

	if (verbose(class)) {
		graph_unlock();

		printk("\nnew class %px: %s", class->key, class->name);
		if (class->name_version > 1)
			printk(KERN_CONT "#%d", class->name_version);
		printk(KERN_CONT "\n");
		dump_stack();

		if (!graph_lock()) {
			return NULL;
		}
	}
out_unlock_set:
	graph_unlock();

out_set_class_cache:
	if (!subclass || force)
		lock->class_cache[0] = class;
	else if (subclass < NR_LOCKDEP_CACHING_CLASSES)
		lock->class_cache[subclass] = class;

	/*
	 * Hash collision, did we smoke some? We found a class with a matching
	 * hash but the subclass -- which is hashed in -- didn't match.
	 */
	if (DEBUG_LOCKS_WARN_ON(class->subclass != subclass))
		return NULL;

	return class;
}

#ifdef CONFIG_PROVE_LOCKING
/*
 * Allocate a lockdep entry. (assumes the graph_lock held, returns
 * with NULL on failure)
 */
static struct lock_list *alloc_list_entry(void)
{
	int idx = find_first_zero_bit(list_entries_in_use,
				      ARRAY_SIZE(list_entries));

	if (idx >= ARRAY_SIZE(list_entries)) {
		if (!debug_locks_off_graph_unlock())
			return NULL;

		print_lockdep_off("BUG: MAX_LOCKDEP_ENTRIES too low!");
		dump_stack();
		return NULL;
	}
	nr_list_entries++;
	__set_bit(idx, list_entries_in_use);
	return list_entries + idx;
}

/*
 * Add a new dependency to the head of the list:
 */
static int add_lock_to_list(struct lock_class *this,
			    struct lock_class *links_to, struct list_head *head,
			    u16 distance, u8 dep,
			    const struct lock_trace *trace)
{
	struct lock_list *entry;
	/*
	 * Lock not present yet - get a new dependency struct and
	 * add it to the list:
	 */
	entry = alloc_list_entry();
	if (!entry)
		return 0;

	entry->class = this;
	entry->links_to = links_to;
	entry->dep = dep;
	entry->distance = distance;
	entry->trace = trace;
	/*
	 * Both allocation and removal are done under the graph lock; but
	 * iteration is under RCU-sched; see look_up_lock_class() and
	 * lockdep_free_key_range().
	 */
	list_add_tail_rcu(&entry->entry, head);

	return 1;
}

/*
 * For good efficiency of modular, we use power of 2
 */
#define MAX_CIRCULAR_QUEUE_SIZE		(1UL << CONFIG_LOCKDEP_CIRCULAR_QUEUE_BITS)
#define CQ_MASK				(MAX_CIRCULAR_QUEUE_SIZE-1)

/*
 * The circular_queue and helpers are used to implement graph
 * breadth-first search (BFS) algorithm, by which we can determine
 * whether there is a path from a lock to another. In deadlock checks,
 * a path from the next lock to be acquired to a previous held lock
 * indicates that adding the <prev> -> <next> lock dependency will
 * produce a circle in the graph. Breadth-first search instead of
 * depth-first search is used in order to find the shortest (circular)
 * path.
 */
struct circular_queue {
	struct lock_list *element[MAX_CIRCULAR_QUEUE_SIZE];
	unsigned int  front, rear;
};

static struct circular_queue lock_cq;

unsigned int max_bfs_queue_depth;

static unsigned int lockdep_dependency_gen_id;

static inline void __cq_init(struct circular_queue *cq)
{
	cq->front = cq->rear = 0;
	lockdep_dependency_gen_id++;
}

static inline int __cq_empty(struct circular_queue *cq)
{
	return (cq->front == cq->rear);
}

static inline int __cq_full(struct circular_queue *cq)
{
	return ((cq->rear + 1) & CQ_MASK) == cq->front;
}

static inline int __cq_enqueue(struct circular_queue *cq, struct lock_list *elem)
{
	if (__cq_full(cq))
		return -1;

	cq->element[cq->rear] = elem;
	cq->rear = (cq->rear + 1) & CQ_MASK;
	return 0;
}

/*
 * Dequeue an element from the circular_queue, return a lock_list if
 * the queue is not empty, or NULL if otherwise.
 */
static inline struct lock_list * __cq_dequeue(struct circular_queue *cq)
{
	struct lock_list * lock;

	if (__cq_empty(cq))
		return NULL;

	lock = cq->element[cq->front];
	cq->front = (cq->front + 1) & CQ_MASK;

	return lock;
}

static inline unsigned int  __cq_get_elem_count(struct circular_queue *cq)
{
	return (cq->rear - cq->front) & CQ_MASK;
}

static inline void mark_lock_accessed(struct lock_list *lock)
{
	lock->class->dep_gen_id = lockdep_dependency_gen_id;
}

static inline void visit_lock_entry(struct lock_list *lock,
				    struct lock_list *parent)
{
	lock->parent = parent;
}

static inline unsigned long lock_accessed(struct lock_list *lock)
{
	return lock->class->dep_gen_id == lockdep_dependency_gen_id;
}

static inline struct lock_list *get_lock_parent(struct lock_list *child)
{
	return child->parent;
}

static inline int get_lock_depth(struct lock_list *child)
{
	int depth = 0;
	struct lock_list *parent;

	while ((parent = get_lock_parent(child))) {
		child = parent;
		depth++;
	}
	return depth;
}

/*
 * Return the forward or backward dependency list.
 *
 * @lock:   the lock_list to get its class's dependency list
 * @offset: the offset to struct lock_class to determine whether it is
 *          locks_after or locks_before
 */
static inline struct list_head *get_dep_list(struct lock_list *lock, int offset)
{
	void *lock_class = lock->class;

	return lock_class + offset;
}
/*
 * Return values of a bfs search:
 *
 * BFS_E* indicates an error
 * BFS_R* indicates a result (match or not)
 *
 * BFS_EINVALIDNODE: Find a invalid node in the graph.
 *
 * BFS_EQUEUEFULL: The queue is full while doing the bfs.
 *
 * BFS_RMATCH: Find the matched node in the graph, and put that node into
 *             *@target_entry.
 *
 * BFS_RNOMATCH: Haven't found the matched node and keep *@target_entry
 *               _unchanged_.
 */
enum bfs_result {
	BFS_EINVALIDNODE = -2,
	BFS_EQUEUEFULL = -1,
	BFS_RMATCH = 0,
	BFS_RNOMATCH = 1,
};

/*
 * bfs_result < 0 means error
 */
static inline bool bfs_error(enum bfs_result res)
{
	return res < 0;
}

/*
 * DEP_*_BIT in lock_list::dep
 *
 * For dependency @prev -> @next:
 *
 *   SR: @prev is shared reader (->read != 0) and @next is recursive reader
 *       (->read == 2)
 *   ER: @prev is exclusive locker (->read == 0) and @next is recursive reader
 *   SN: @prev is shared reader and @next is non-recursive locker (->read != 2)
 *   EN: @prev is exclusive locker and @next is non-recursive locker
 *
 * Note that we define the value of DEP_*_BITs so that:
 *   bit0 is prev->read == 0
 *   bit1 is next->read != 2
 */
#define DEP_SR_BIT (0 + (0 << 1)) /* 0 */
#define DEP_ER_BIT (1 + (0 << 1)) /* 1 */
#define DEP_SN_BIT (0 + (1 << 1)) /* 2 */
#define DEP_EN_BIT (1 + (1 << 1)) /* 3 */

#define DEP_SR_MASK (1U << (DEP_SR_BIT))
#define DEP_ER_MASK (1U << (DEP_ER_BIT))
#define DEP_SN_MASK (1U << (DEP_SN_BIT))
#define DEP_EN_MASK (1U << (DEP_EN_BIT))

static inline unsigned int
__calc_dep_bit(struct held_lock *prev, struct held_lock *next)
{
	return (prev->read == 0) + ((next->read != 2) << 1);
}

static inline u8 calc_dep(struct held_lock *prev, struct held_lock *next)
{
	return 1U << __calc_dep_bit(prev, next);
}

/*
 * calculate the dep_bit for backwards edges. We care about whether @prev is
 * shared and whether @next is recursive.
 */
static inline unsigned int
__calc_dep_bitb(struct held_lock *prev, struct held_lock *next)
{
	return (next->read != 2) + ((prev->read == 0) << 1);
}

static inline u8 calc_depb(struct held_lock *prev, struct held_lock *next)
{
	return 1U << __calc_dep_bitb(prev, next);
}

/*
 * Initialize a lock_list entry @lock belonging to @class as the root for a BFS
 * search.
 */
static inline void __bfs_init_root(struct lock_list *lock,
				   struct lock_class *class)
{
	lock->class = class;
	lock->parent = NULL;
	lock->only_xr = 0;
}

/*
 * Initialize a lock_list entry @lock based on a lock acquisition @hlock as the
 * root for a BFS search.
 *
 * ->only_xr of the initial lock node is set to @hlock->read == 2, to make sure
 * that <prev> -> @hlock and @hlock -> <whatever __bfs() found> is not -(*R)->
 * and -(S*)->.
 */
static inline void bfs_init_root(struct lock_list *lock,
				 struct held_lock *hlock)
{
	__bfs_init_root(lock, hlock_class(hlock));
	lock->only_xr = (hlock->read == 2);
}

/*
 * Similar to bfs_init_root() but initialize the root for backwards BFS.
 *
 * ->only_xr of the initial lock node is set to @hlock->read != 0, to make sure
 * that <next> -> @hlock and @hlock -> <whatever backwards BFS found> is not
 * -(*S)-> and -(R*)-> (reverse order of -(*R)-> and -(S*)->).
 */
static inline void bfs_init_rootb(struct lock_list *lock,
				  struct held_lock *hlock)
{
	__bfs_init_root(lock, hlock_class(hlock));
	lock->only_xr = (hlock->read != 0);
}

static inline struct lock_list *__bfs_next(struct lock_list *lock, int offset)
{
	if (!lock || !lock->parent)
		return NULL;

	return list_next_or_null_rcu(get_dep_list(lock->parent, offset),
				     &lock->entry, struct lock_list, entry);
}

/*
 * Breadth-First Search to find a strong path in the dependency graph.
 *
 * @source_entry: the source of the path we are searching for.
 * @data: data used for the second parameter of @match function
 * @match: match function for the search
 * @target_entry: pointer to the target of a matched path
 * @offset: the offset to struct lock_class to determine whether it is
 *          locks_after or locks_before
 *
 * We may have multiple edges (considering different kinds of dependencies,
 * e.g. ER and SN) between two nodes in the dependency graph. But
 * only the strong dependency path in the graph is relevant to deadlocks. A
 * strong dependency path is a dependency path that doesn't have two adjacent
 * dependencies as -(*R)-> -(S*)->, please see:
 *
 *         Documentation/locking/lockdep-design.rst
 *
 * for more explanation of the definition of strong dependency paths
 *
 * In __bfs(), we only traverse in the strong dependency path:
 *
 *     In lock_list::only_xr, we record whether the previous dependency only
 *     has -(*R)-> in the search, and if it does (prev only has -(*R)->), we
 *     filter out any -(S*)-> in the current dependency and after that, the
 *     ->only_xr is set according to whether we only have -(*R)-> left.
 */
static enum bfs_result __bfs(struct lock_list *source_entry,
			     void *data,
			     bool (*match)(struct lock_list *entry, void *data),
			     bool (*skip)(struct lock_list *entry, void *data),
			     struct lock_list **target_entry,
			     int offset)
{
	struct circular_queue *cq = &lock_cq;
	struct lock_list *lock = NULL;
	struct lock_list *entry;
	struct list_head *head;
	unsigned int cq_depth;
	bool first;

	lockdep_assert_locked();

	__cq_init(cq);
	__cq_enqueue(cq, source_entry);

	while ((lock = __bfs_next(lock, offset)) || (lock = __cq_dequeue(cq))) {
		if (!lock->class)
			return BFS_EINVALIDNODE;

		/*
		 * Step 1: check whether we already finish on this one.
		 *
		 * If we have visited all the dependencies from this @lock to
		 * others (iow, if we have visited all lock_list entries in
		 * @lock->class->locks_{after,before}) we skip, otherwise go
		 * and visit all the dependencies in the list and mark this
		 * list accessed.
		 */
		if (lock_accessed(lock))
			continue;
		else
			mark_lock_accessed(lock);

		/*
		 * Step 2: check whether prev dependency and this form a strong
		 *         dependency path.
		 */
		if (lock->parent) { /* Parent exists, check prev dependency */
			u8 dep = lock->dep;
			bool prev_only_xr = lock->parent->only_xr;

			/*
			 * Mask out all -(S*)-> if we only have *R in previous
			 * step, because -(*R)-> -(S*)-> don't make up a strong
			 * dependency.
			 */
			if (prev_only_xr)
				dep &= ~(DEP_SR_MASK | DEP_SN_MASK);

			/* If nothing left, we skip */
			if (!dep)
				continue;

			/* If there are only -(*R)-> left, set that for the next step */
			lock->only_xr = !(dep & (DEP_SN_MASK | DEP_EN_MASK));
		}

		/*
		 * Step 3: we haven't visited this and there is a strong
		 *         dependency path to this, so check with @match.
		 *         If @skip is provide and returns true, we skip this
		 *         lock (and any path this lock is in).
		 */
		if (skip && skip(lock, data))
			continue;

		if (match(lock, data)) {
			*target_entry = lock;
			return BFS_RMATCH;
		}

		/*
		 * Step 4: if not match, expand the path by adding the
		 *         forward or backwards dependencies in the search
		 *
		 */
		first = true;
		head = get_dep_list(lock, offset);
		list_for_each_entry_rcu(entry, head, entry) {
			visit_lock_entry(entry, lock);

			/*
			 * Note we only enqueue the first of the list into the
			 * queue, because we can always find a sibling
			 * dependency from one (see __bfs_next()), as a result
			 * the space of queue is saved.
			 */
			if (!first)
				continue;

			first = false;

			if (__cq_enqueue(cq, entry))
				return BFS_EQUEUEFULL;

			cq_depth = __cq_get_elem_count(cq);
			if (max_bfs_queue_depth < cq_depth)
				max_bfs_queue_depth = cq_depth;
		}
	}

	return BFS_RNOMATCH;
}

static inline enum bfs_result
__bfs_forwards(struct lock_list *src_entry,
	       void *data,
	       bool (*match)(struct lock_list *entry, void *data),
	       bool (*skip)(struct lock_list *entry, void *data),
	       struct lock_list **target_entry)
{
	return __bfs(src_entry, data, match, skip, target_entry,
		     offsetof(struct lock_class, locks_after));

}

static inline enum bfs_result
__bfs_backwards(struct lock_list *src_entry,
		void *data,
		bool (*match)(struct lock_list *entry, void *data),
	       bool (*skip)(struct lock_list *entry, void *data),
		struct lock_list **target_entry)
{
	return __bfs(src_entry, data, match, skip, target_entry,
		     offsetof(struct lock_class, locks_before));

}

static void print_lock_trace(const struct lock_trace *trace,
			     unsigned int spaces)
{
	stack_trace_print(trace->entries, trace->nr_entries, spaces);
}

/*
 * Print a dependency chain entry (this is only done when a deadlock
 * has been detected):
 */
static noinline void
print_circular_bug_entry(struct lock_list *target, int depth)
{
	if (debug_locks_silent)
		return;
	printk("\n-> #%u", depth);
	print_lock_name(NULL, target->class);
	printk(KERN_CONT ":\n");
	print_lock_trace(target->trace, 6);
}

static void
print_circular_lock_scenario(struct held_lock *src,
			     struct held_lock *tgt,
			     struct lock_list *prt)
{
	struct lock_class *source = hlock_class(src);
	struct lock_class *target = hlock_class(tgt);
	struct lock_class *parent = prt->class;
	int src_read = src->read;
	int tgt_read = tgt->read;

	/*
	 * A direct locking problem where unsafe_class lock is taken
	 * directly by safe_class lock, then all we need to show
	 * is the deadlock scenario, as it is obvious that the
	 * unsafe lock is taken under the safe lock.
	 *
	 * But if there is a chain instead, where the safe lock takes
	 * an intermediate lock (middle_class) where this lock is
	 * not the same as the safe lock, then the lock chain is
	 * used to describe the problem. Otherwise we would need
	 * to show a different CPU case for each link in the chain
	 * from the safe_class lock to the unsafe_class lock.
	 */
	if (parent != source) {
		printk("Chain exists of:\n  ");
		__print_lock_name(src, source);
		printk(KERN_CONT " --> ");
		__print_lock_name(NULL, parent);
		printk(KERN_CONT " --> ");
		__print_lock_name(tgt, target);
		printk(KERN_CONT "\n\n");
	}

	printk(" Possible unsafe locking scenario:\n\n");
	printk("       CPU0                    CPU1\n");
	printk("       ----                    ----\n");
	if (tgt_read != 0)
		printk("  rlock(");
	else
		printk("  lock(");
	__print_lock_name(tgt, target);
	printk(KERN_CONT ");\n");
	printk("                               lock(");
	__print_lock_name(NULL, parent);
	printk(KERN_CONT ");\n");
	printk("                               lock(");
	__print_lock_name(tgt, target);
	printk(KERN_CONT ");\n");
	if (src_read != 0)
		printk("  rlock(");
	else if (src->sync)
		printk("  sync(");
	else
		printk("  lock(");
	__print_lock_name(src, source);
	printk(KERN_CONT ");\n");
	printk("\n *** DEADLOCK ***\n\n");
}

/*
 * When a circular dependency is detected, print the
 * header first:
 */
static noinline void
print_circular_bug_header(struct lock_list *entry, unsigned int depth,
			struct held_lock *check_src,
			struct held_lock *check_tgt)
{
	struct task_struct *curr = current;

	if (debug_locks_silent)
		return;

	pr_warn("\n");
	pr_warn("======================================================\n");
	pr_warn("WARNING: possible circular locking dependency detected\n");
	print_kernel_ident();
	pr_warn("------------------------------------------------------\n");
	pr_warn("%s/%d is trying to acquire lock:\n",
		curr->comm, task_pid_nr(curr));
	print_lock(check_src);

	pr_warn("\nbut task is already holding lock:\n");

	print_lock(check_tgt);
	pr_warn("\nwhich lock already depends on the new lock.\n\n");
	pr_warn("\nthe existing dependency chain (in reverse order) is:\n");

	print_circular_bug_entry(entry, depth);
}

/*
 * We are about to add A -> B into the dependency graph, and in __bfs() a
 * strong dependency path A -> .. -> B is found: hlock_class equals
 * entry->class.
 *
 * If A -> .. -> B can replace A -> B in any __bfs() search (means the former
 * is _stronger_ than or equal to the latter), we consider A -> B as redundant.
 * For example if A -> .. -> B is -(EN)-> (i.e. A -(E*)-> .. -(*N)-> B), and A
 * -> B is -(ER)-> or -(EN)->, then we don't need to add A -> B into the
 * dependency graph, as any strong path ..-> A -> B ->.. we can get with
 * having dependency A -> B, we could already get a equivalent path ..-> A ->
 * .. -> B -> .. with A -> .. -> B. Therefore A -> B is redundant.
 *
 * We need to make sure both the start and the end of A -> .. -> B is not
 * weaker than A -> B. For the start part, please see the comment in
 * check_redundant(). For the end part, we need:
 *
 * Either
 *
 *     a) A -> B is -(*R)-> (everything is not weaker than that)
 *
 * or
 *
 *     b) A -> .. -> B is -(*N)-> (nothing is stronger than this)
 *
 */
static inline bool hlock_equal(struct lock_list *entry, void *data)
{
	struct held_lock *hlock = (struct held_lock *)data;

	return hlock_class(hlock) == entry->class && /* Found A -> .. -> B */
	       (hlock->read == 2 ||  /* A -> B is -(*R)-> */
		!entry->only_xr); /* A -> .. -> B is -(*N)-> */
}

/*
 * We are about to add B -> A into the dependency graph, and in __bfs() a
 * strong dependency path A -> .. -> B is found: hlock_class equals
 * entry->class.
 *
 * We will have a deadlock case (conflict) if A -> .. -> B -> A is a strong
 * dependency cycle, that means:
 *
 * Either
 *
 *     a) B -> A is -(E*)->
 *
 * or
 *
 *     b) A -> .. -> B is -(*N)-> (i.e. A -> .. -(*N)-> B)
 *
 * as then we don't have -(*R)-> -(S*)-> in the cycle.
 */
static inline bool hlock_conflict(struct lock_list *entry, void *data)
{
	struct held_lock *hlock = (struct held_lock *)data;

	return hlock_class(hlock) == entry->class && /* Found A -> .. -> B */
	       (hlock->read == 0 || /* B -> A is -(E*)-> */
		!entry->only_xr); /* A -> .. -> B is -(*N)-> */
}

static noinline void print_circular_bug(struct lock_list *this,
				struct lock_list *target,
				struct held_lock *check_src,
				struct held_lock *check_tgt)
{
	struct task_struct *curr = current;
	struct lock_list *parent;
	struct lock_list *first_parent;
	int depth;

	if (!debug_locks_off_graph_unlock() || debug_locks_silent)
		return;

	this->trace = save_trace();
	if (!this->trace)
		return;

	depth = get_lock_depth(target);

	print_circular_bug_header(target, depth, check_src, check_tgt);

	parent = get_lock_parent(target);
	first_parent = parent;

	while (parent) {
		print_circular_bug_entry(parent, --depth);
		parent = get_lock_parent(parent);
	}

	printk("\nother info that might help us debug this:\n\n");
	print_circular_lock_scenario(check_src, check_tgt,
				     first_parent);

	lockdep_print_held_locks(curr);

	printk("\nstack backtrace:\n");
	dump_stack();
}

static noinline void print_bfs_bug(int ret)
{
	if (!debug_locks_off_graph_unlock())
		return;

	/*
	 * Breadth-first-search failed, graph got corrupted?
	 */
	WARN(1, "lockdep bfs error:%d\n", ret);
}

static bool noop_count(struct lock_list *entry, void *data)
{
	(*(unsigned long *)data)++;
	return false;
}

static unsigned long __lockdep_count_forward_deps(struct lock_list *this)
{
	unsigned long  count = 0;
	struct lock_list *target_entry;

	__bfs_forwards(this, (void *)&count, noop_count, NULL, &target_entry);

	return count;
}
unsigned long lockdep_count_forward_deps(struct lock_class *class)
{
	unsigned long ret, flags;
	struct lock_list this;

	__bfs_init_root(&this, class);

	raw_local_irq_save(flags);
	lockdep_lock();
	ret = __lockdep_count_forward_deps(&this);
	lockdep_unlock();
	raw_local_irq_restore(flags);

	return ret;
}

static unsigned long __lockdep_count_backward_deps(struct lock_list *this)
{
	unsigned long  count = 0;
	struct lock_list *target_entry;

	__bfs_backwards(this, (void *)&count, noop_count, NULL, &target_entry);

	return count;
}

unsigned long lockdep_count_backward_deps(struct lock_class *class)
{
	unsigned long ret, flags;
	struct lock_list this;

	__bfs_init_root(&this, class);

	raw_local_irq_save(flags);
	lockdep_lock();
	ret = __lockdep_count_backward_deps(&this);
	lockdep_unlock();
	raw_local_irq_restore(flags);

	return ret;
}

/*
 * Check that the dependency graph starting at <src> can lead to
 * <target> or not.
 */
static noinline enum bfs_result
check_path(struct held_lock *target, struct lock_list *src_entry,
	   bool (*match)(struct lock_list *entry, void *data),
	   bool (*skip)(struct lock_list *entry, void *data),
	   struct lock_list **target_entry)
{
	enum bfs_result ret;

	ret = __bfs_forwards(src_entry, target, match, skip, target_entry);

	if (unlikely(bfs_error(ret)))
		print_bfs_bug(ret);

	return ret;
}

static void print_deadlock_bug(struct task_struct *, struct held_lock *, struct held_lock *);

/*
 * Prove that the dependency graph starting at <src> can not
 * lead to <target>. If it can, there is a circle when adding
 * <target> -> <src> dependency.
 *
 * Print an error and return BFS_RMATCH if it does.
 */
static noinline enum bfs_result
check_noncircular(struct held_lock *src, struct held_lock *target,
		  struct lock_trace **const trace)
{
	enum bfs_result ret;
	struct lock_list *target_entry;
	struct lock_list src_entry;

	bfs_init_root(&src_entry, src);

	debug_atomic_inc(nr_cyclic_checks);

	ret = check_path(target, &src_entry, hlock_conflict, NULL, &target_entry);

	if (unlikely(ret == BFS_RMATCH)) {
		if (!*trace) {
			/*
			 * If save_trace fails here, the printing might
			 * trigger a WARN but because of the !nr_entries it
			 * should not do bad things.
			 */
			*trace = save_trace();
		}

		if (src->class_idx == target->class_idx)
			print_deadlock_bug(current, src, target);
		else
			print_circular_bug(&src_entry, target_entry, src, target);
	}

	return ret;
}

#ifdef CONFIG_TRACE_IRQFLAGS

/*
 * Forwards and backwards subgraph searching, for the purposes of
 * proving that two subgraphs can be connected by a new dependency
 * without creating any illegal irq-safe -> irq-unsafe lock dependency.
 *
 * A irq safe->unsafe deadlock happens with the following conditions:
 *
 * 1) We have a strong dependency path A -> ... -> B
 *
 * 2) and we have ENABLED_IRQ usage of B and USED_IN_IRQ usage of A, therefore
 *    irq can create a new dependency B -> A (consider the case that a holder
 *    of B gets interrupted by an irq whose handler will try to acquire A).
 *
 * 3) the dependency circle A -> ... -> B -> A we get from 1) and 2) is a
 *    strong circle:
 *
 *      For the usage bits of B:
 *        a) if A -> B is -(*N)->, then B -> A could be any type, so any
 *           ENABLED_IRQ usage suffices.
 *        b) if A -> B is -(*R)->, then B -> A must be -(E*)->, so only
 *           ENABLED_IRQ_*_READ usage suffices.
 *
 *      For the usage bits of A:
 *        c) if A -> B is -(E*)->, then B -> A could be any type, so any
 *           USED_IN_IRQ usage suffices.
 *        d) if A -> B is -(S*)->, then B -> A must be -(*N)->, so only
 *           USED_IN_IRQ_*_READ usage suffices.
 */

/*
 * There is a strong dependency path in the dependency graph: A -> B, and now
 * we need to decide which usage bit of A should be accumulated to detect
 * safe->unsafe bugs.
 *
 * Note that usage_accumulate() is used in backwards search, so ->only_xr
 * stands for whether A -> B only has -(S*)-> (in this case ->only_xr is true).
 *
 * As above, if only_xr is false, which means A -> B has -(E*)-> dependency
 * path, any usage of A should be considered. Otherwise, we should only
 * consider _READ usage.
 */
static inline bool usage_accumulate(struct lock_list *entry, void *mask)
{
	if (!entry->only_xr)
		*(unsigned long *)mask |= entry->class->usage_mask;
	else /* Mask out _READ usage bits */
		*(unsigned long *)mask |= (entry->class->usage_mask & LOCKF_IRQ);

	return false;
}

/*
 * There is a strong dependency path in the dependency graph: A -> B, and now
 * we need to decide which usage bit of B conflicts with the usage bits of A,
 * i.e. which usage bit of B may introduce safe->unsafe deadlocks.
 *
 * As above, if only_xr is false, which means A -> B has -(*N)-> dependency
 * path, any usage of B should be considered. Otherwise, we should only
 * consider _READ usage.
 */
static inline bool usage_match(struct lock_list *entry, void *mask)
{
	if (!entry->only_xr)
		return !!(entry->class->usage_mask & *(unsigned long *)mask);
	else /* Mask out _READ usage bits */
		return !!((entry->class->usage_mask & LOCKF_IRQ) & *(unsigned long *)mask);
}

static inline bool usage_skip(struct lock_list *entry, void *mask)
{
	if (entry->class->lock_type == LD_LOCK_NORMAL)
		return false;

	/*
	 * Skip local_lock() for irq inversion detection.
	 *
	 * For !RT, local_lock() is not a real lock, so it won't carry any
	 * dependency.
	 *
	 * For RT, an irq inversion happens when we have lock A and B, and on
	 * some CPU we can have:
	 *
	 *	lock(A);
	 *	<interrupted>
	 *	  lock(B);
	 *
	 * where lock(B) cannot sleep, and we have a dependency B -> ... -> A.
	 *
	 * Now we prove local_lock() cannot exist in that dependency. First we
	 * have the observation for any lock chain L1 -> ... -> Ln, for any
	 * 1 <= i <= n, Li.inner_wait_type <= L1.inner_wait_type, otherwise
	 * wait context check will complain. And since B is not a sleep lock,
	 * therefore B.inner_wait_type >= 2, and since the inner_wait_type of
	 * local_lock() is 3, which is greater than 2, therefore there is no
	 * way the local_lock() exists in the dependency B -> ... -> A.
	 *
	 * As a result, we will skip local_lock(), when we search for irq
	 * inversion bugs.
	 */
	if (entry->class->lock_type == LD_LOCK_PERCPU &&
	    DEBUG_LOCKS_WARN_ON(entry->class->wait_type_inner < LD_WAIT_CONFIG))
		return false;

	/*
	 * Skip WAIT_OVERRIDE for irq inversion detection -- it's not actually
	 * a lock and only used to override the wait_type.
	 */

	return true;
}

/*
 * Find a node in the forwards-direction dependency sub-graph starting
 * at @root->class that matches @bit.
 *
 * Return BFS_MATCH if such a node exists in the subgraph, and put that node
 * into *@target_entry.
 */
static enum bfs_result
find_usage_forwards(struct lock_list *root, unsigned long usage_mask,
			struct lock_list **target_entry)
{
	enum bfs_result result;

	debug_atomic_inc(nr_find_usage_forwards_checks);

	result = __bfs_forwards(root, &usage_mask, usage_match, usage_skip, target_entry);

	return result;
}

/*
 * Find a node in the backwards-direction dependency sub-graph starting
 * at @root->class that matches @bit.
 */
static enum bfs_result
find_usage_backwards(struct lock_list *root, unsigned long usage_mask,
			struct lock_list **target_entry)
{
	enum bfs_result result;

	debug_atomic_inc(nr_find_usage_backwards_checks);

	result = __bfs_backwards(root, &usage_mask, usage_match, usage_skip, target_entry);

	return result;
}

static void print_lock_class_header(struct lock_class *class, int depth)
{
	int bit;

	printk("%*s->", depth, "");
	print_lock_name(NULL, class);
#ifdef CONFIG_DEBUG_LOCKDEP
	printk(KERN_CONT " ops: %lu", debug_class_ops_read(class));
#endif
	printk(KERN_CONT " {\n");

	for (bit = 0; bit < LOCK_TRACE_STATES; bit++) {
		if (class->usage_mask & (1 << bit)) {
			int len = depth;

			len += printk("%*s   %s", depth, "", usage_str[bit]);
			len += printk(KERN_CONT " at:\n");
			print_lock_trace(class->usage_traces[bit], len);
		}
	}
	printk("%*s }\n", depth, "");

	printk("%*s ... key      at: [<%px>] %pS\n",
		depth, "", class->key, class->key);
}

/*
 * Dependency path printing:
 *
 * After BFS we get a lock dependency path (linked via ->parent of lock_list),
 * printing out each lock in the dependency path will help on understanding how
 * the deadlock could happen. Here are some details about dependency path
 * printing:
 *
 * 1)	A lock_list can be either forwards or backwards for a lock dependency,
 * 	for a lock dependency A -> B, there are two lock_lists:
 *
 * 	a)	lock_list in the ->locks_after list of A, whose ->class is B and
 * 		->links_to is A. In this case, we can say the lock_list is
 * 		"A -> B" (forwards case).
 *
 * 	b)	lock_list in the ->locks_before list of B, whose ->class is A
 * 		and ->links_to is B. In this case, we can say the lock_list is
 * 		"B <- A" (bacwards case).
 *
 * 	The ->trace of both a) and b) point to the call trace where B was
 * 	acquired with A held.
 *
 * 2)	A "helper" lock_list is introduced during BFS, this lock_list doesn't
 * 	represent a certain lock dependency, it only provides an initial entry
 * 	for BFS. For example, BFS may introduce a "helper" lock_list whose
 * 	->class is A, as a result BFS will search all dependencies starting with
 * 	A, e.g. A -> B or A -> C.
 *
 * 	The notation of a forwards helper lock_list is like "-> A", which means
 * 	we should search the forwards dependencies starting with "A", e.g A -> B
 * 	or A -> C.
 *
 * 	The notation of a bacwards helper lock_list is like "<- B", which means
 * 	we should search the backwards dependencies ending with "B", e.g.
 * 	B <- A or B <- C.
 */

/*
 * printk the shortest lock dependencies from @root to @leaf in reverse order.
 *
 * We have a lock dependency path as follow:
 *
 *    @root                                                                 @leaf
 *      |                                                                     |
 *      V                                                                     V
 *	          ->parent                                   ->parent
 * | lock_list | <--------- | lock_list | ... | lock_list  | <--------- | lock_list |
 * |    -> L1  |            | L1 -> L2  | ... |Ln-2 -> Ln-1|            | Ln-1 -> Ln|
 *
 * , so it's natural that we start from @leaf and print every ->class and
 * ->trace until we reach the @root.
 */
static void __used
print_shortest_lock_dependencies(struct lock_list *leaf,
				 struct lock_list *root)
{
	struct lock_list *entry = leaf;
	int depth;

	/*compute depth from generated tree by BFS*/
	depth = get_lock_depth(leaf);

	do {
		print_lock_class_header(entry->class, depth);
		printk("%*s ... acquired at:\n", depth, "");
		print_lock_trace(entry->trace, 2);
		printk("\n");

		if (depth == 0 && (entry != root)) {
			printk("lockdep:%s bad path found in chain graph\n", __func__);
			break;
		}

		entry = get_lock_parent(entry);
		depth--;
	} while (entry && (depth >= 0));
}

/*
 * printk the shortest lock dependencies from @leaf to @root.
 *
 * We have a lock dependency path (from a backwards search) as follow:
 *
 *    @leaf                                                                 @root
 *      |                                                                     |
 *      V                                                                     V
 *	          ->parent                                   ->parent
 * | lock_list | ---------> | lock_list | ... | lock_list  | ---------> | lock_list |
 * | L2 <- L1  |            | L3 <- L2  | ... | Ln <- Ln-1 |            |    <- Ln  |
 *
 * , so when we iterate from @leaf to @root, we actually print the lock
 * dependency path L1 -> L2 -> .. -> Ln in the non-reverse order.
 *
 * Another thing to notice here is that ->class of L2 <- L1 is L1, while the
 * ->trace of L2 <- L1 is the call trace of L2, in fact we don't have the call
 * trace of L1 in the dependency path, which is alright, because most of the
 * time we can figure out where L1 is held from the call trace of L2.
 */
static void __used
print_shortest_lock_dependencies_backwards(struct lock_list *leaf,
					   struct lock_list *root)
{
	struct lock_list *entry = leaf;
	const struct lock_trace *trace = NULL;
	int depth;

	/*compute depth from generated tree by BFS*/
	depth = get_lock_depth(leaf);

	do {
		print_lock_class_header(entry->class, depth);
		if (trace) {
			printk("%*s ... acquired at:\n", depth, "");
			print_lock_trace(trace, 2);
			printk("\n");
		}

		/*
		 * Record the pointer to the trace for the next lock_list
		 * entry, see the comments for the function.
		 */
		trace = entry->trace;

		if (depth == 0 && (entry != root)) {
			printk("lockdep:%s bad path found in chain graph\n", __func__);
			break;
		}

		entry = get_lock_parent(entry);
		depth--;
	} while (entry && (depth >= 0));
}

static void
print_irq_lock_scenario(struct lock_list *safe_entry,
			struct lock_list *unsafe_entry,
			struct lock_class *prev_class,
			struct lock_class *next_class)
{
	struct lock_class *safe_class = safe_entry->class;
	struct lock_class *unsafe_class = unsafe_entry->class;
	struct lock_class *middle_class = prev_class;

	if (middle_class == safe_class)
		middle_class = next_class;

	/*
	 * A direct locking problem where unsafe_class lock is taken
	 * directly by safe_class lock, then all we need to show
	 * is the deadlock scenario, as it is obvious that the
	 * unsafe lock is taken under the safe lock.
	 *
	 * But if there is a chain instead, where the safe lock takes
	 * an intermediate lock (middle_class) where this lock is
	 * not the same as the safe lock, then the lock chain is
	 * used to describe the problem. Otherwise we would need
	 * to show a different CPU case for each link in the chain
	 * from the safe_class lock to the unsafe_class lock.
	 */
	if (middle_class != unsafe_class) {
		printk("Chain exists of:\n  ");
		__print_lock_name(NULL, safe_class);
		printk(KERN_CONT " --> ");
		__print_lock_name(NULL, middle_class);
		printk(KERN_CONT " --> ");
		__print_lock_name(NULL, unsafe_class);
		printk(KERN_CONT "\n\n");
	}

	printk(" Possible interrupt unsafe locking scenario:\n\n");
	printk("       CPU0                    CPU1\n");
	printk("       ----                    ----\n");
	printk("  lock(");
	__print_lock_name(NULL, unsafe_class);
	printk(KERN_CONT ");\n");
	printk("                               local_irq_disable();\n");
	printk("                               lock(");
	__print_lock_name(NULL, safe_class);
	printk(KERN_CONT ");\n");
	printk("                               lock(");
	__print_lock_name(NULL, middle_class);
	printk(KERN_CONT ");\n");
	printk("  <Interrupt>\n");
	printk("    lock(");
	__print_lock_name(NULL, safe_class);
	printk(KERN_CONT ");\n");
	printk("\n *** DEADLOCK ***\n\n");
}

static void
print_bad_irq_dependency(struct task_struct *curr,
			 struct lock_list *prev_root,
			 struct lock_list *next_root,
			 struct lock_list *backwards_entry,
			 struct lock_list *forwards_entry,
			 struct held_lock *prev,
			 struct held_lock *next,
			 enum lock_usage_bit bit1,
			 enum lock_usage_bit bit2,
			 const char *irqclass)
{
	if (!debug_locks_off_graph_unlock() || debug_locks_silent)
		return;

	pr_warn("\n");
	pr_warn("=====================================================\n");
	pr_warn("WARNING: %s-safe -> %s-unsafe lock order detected\n",
		irqclass, irqclass);
	print_kernel_ident();
	pr_warn("-----------------------------------------------------\n");
	pr_warn("%s/%d [HC%u[%lu]:SC%u[%lu]:HE%u:SE%u] is trying to acquire:\n",
		curr->comm, task_pid_nr(curr),
		lockdep_hardirq_context(), hardirq_count() >> HARDIRQ_SHIFT,
		curr->softirq_context, softirq_count() >> SOFTIRQ_SHIFT,
		lockdep_hardirqs_enabled(),
		curr->softirqs_enabled);
	print_lock(next);

	pr_warn("\nand this task is already holding:\n");
	print_lock(prev);
	pr_warn("which would create a new lock dependency:\n");
	print_lock_name(prev, hlock_class(prev));
	pr_cont(" ->");
	print_lock_name(next, hlock_class(next));
	pr_cont("\n");

	pr_warn("\nbut this new dependency connects a %s-irq-safe lock:\n",
		irqclass);
	print_lock_name(NULL, backwards_entry->class);
	pr_warn("\n... which became %s-irq-safe at:\n", irqclass);

	print_lock_trace(backwards_entry->class->usage_traces[bit1], 1);

	pr_warn("\nto a %s-irq-unsafe lock:\n", irqclass);
	print_lock_name(NULL, forwards_entry->class);
	pr_warn("\n... which became %s-irq-unsafe at:\n", irqclass);
	pr_warn("...");

	print_lock_trace(forwards_entry->class->usage_traces[bit2], 1);

	pr_warn("\nother info that might help us debug this:\n\n");
	print_irq_lock_scenario(backwards_entry, forwards_entry,
				hlock_class(prev), hlock_class(next));

	lockdep_print_held_locks(curr);

	pr_warn("\nthe dependencies between %s-irq-safe lock and the holding lock:\n", irqclass);
	print_shortest_lock_dependencies_backwards(backwards_entry, prev_root);

	pr_warn("\nthe dependencies between the lock to be acquired");
	pr_warn(" and %s-irq-unsafe lock:\n", irqclass);
	next_root->trace = save_trace();
	if (!next_root->trace)
		return;
	print_shortest_lock_dependencies(forwards_entry, next_root);

	pr_warn("\nstack backtrace:\n");
	dump_stack();
}

static const char *state_names[] = {
#define LOCKDEP_STATE(__STATE) \
	__stringify(__STATE),
#include "lockdep_states.h"
#undef LOCKDEP_STATE
};

static const char *state_rnames[] = {
#define LOCKDEP_STATE(__STATE) \
	__stringify(__STATE)"-READ",
#include "lockdep_states.h"
#undef LOCKDEP_STATE
};

static inline const char *state_name(enum lock_usage_bit bit)
{
	if (bit & LOCK_USAGE_READ_MASK)
		return state_rnames[bit >> LOCK_USAGE_DIR_MASK];
	else
		return state_names[bit >> LOCK_USAGE_DIR_MASK];
}

/*
 * The bit number is encoded like:
 *
 *  bit0: 0 exclusive, 1 read lock
 *  bit1: 0 used in irq, 1 irq enabled
 *  bit2-n: state
 */
static int exclusive_bit(int new_bit)
{
	int state = new_bit & LOCK_USAGE_STATE_MASK;
	int dir = new_bit & LOCK_USAGE_DIR_MASK;

	/*
	 * keep state, bit flip the direction and strip read.
	 */
	return state | (dir ^ LOCK_USAGE_DIR_MASK);
}

/*
 * Observe that when given a bitmask where each bitnr is encoded as above, a
 * right shift of the mask transforms the individual bitnrs as -1 and
 * conversely, a left shift transforms into +1 for the individual bitnrs.
 *
 * So for all bits whose number have LOCK_ENABLED_* set (bitnr1 == 1), we can
 * create the mask with those bit numbers using LOCK_USED_IN_* (bitnr1 == 0)
 * instead by subtracting the bit number by 2, or shifting the mask right by 2.
 *
 * Similarly, bitnr1 == 0 becomes bitnr1 == 1 by adding 2, or shifting left 2.
 *
 * So split the mask (note that LOCKF_ENABLED_IRQ_ALL|LOCKF_USED_IN_IRQ_ALL is
 * all bits set) and recompose with bitnr1 flipped.
 */
static unsigned long invert_dir_mask(unsigned long mask)
{
	unsigned long excl = 0;

	/* Invert dir */
	excl |= (mask & LOCKF_ENABLED_IRQ_ALL) >> LOCK_USAGE_DIR_MASK;
	excl |= (mask & LOCKF_USED_IN_IRQ_ALL) << LOCK_USAGE_DIR_MASK;

	return excl;
}

/*
 * Note that a LOCK_ENABLED_IRQ_*_READ usage and a LOCK_USED_IN_IRQ_*_READ
 * usage may cause deadlock too, for example:
 *
 * P1				P2
 * <irq disabled>
 * write_lock(l1);		<irq enabled>
 *				read_lock(l2);
 * write_lock(l2);
 * 				<in irq>
 * 				read_lock(l1);
 *
 * , in above case, l1 will be marked as LOCK_USED_IN_IRQ_HARDIRQ_READ and l2
 * will marked as LOCK_ENABLE_IRQ_HARDIRQ_READ, and this is a possible
 * deadlock.
 *
 * In fact, all of the following cases may cause deadlocks:
 *
 * 	 LOCK_USED_IN_IRQ_* -> LOCK_ENABLED_IRQ_*
 * 	 LOCK_USED_IN_IRQ_*_READ -> LOCK_ENABLED_IRQ_*
 * 	 LOCK_USED_IN_IRQ_* -> LOCK_ENABLED_IRQ_*_READ
 * 	 LOCK_USED_IN_IRQ_*_READ -> LOCK_ENABLED_IRQ_*_READ
 *
 * As a result, to calculate the "exclusive mask", first we invert the
 * direction (USED_IN/ENABLED) of the original mask, and 1) for all bits with
 * bitnr0 set (LOCK_*_READ), add those with bitnr0 cleared (LOCK_*). 2) for all
 * bits with bitnr0 cleared (LOCK_*_READ), add those with bitnr0 set (LOCK_*).
 */
static unsigned long exclusive_mask(unsigned long mask)
{
	unsigned long excl = invert_dir_mask(mask);

	excl |= (excl & LOCKF_IRQ_READ) >> LOCK_USAGE_READ_MASK;
	excl |= (excl & LOCKF_IRQ) << LOCK_USAGE_READ_MASK;

	return excl;
}

/*
 * Retrieve the _possible_ original mask to which @mask is
 * exclusive. Ie: this is the opposite of exclusive_mask().
 * Note that 2 possible original bits can match an exclusive
 * bit: one has LOCK_USAGE_READ_MASK set, the other has it
 * cleared. So both are returned for each exclusive bit.
 */
static unsigned long original_mask(unsigned long mask)
{
	unsigned long excl = invert_dir_mask(mask);

	/* Include read in existing usages */
	excl |= (excl & LOCKF_IRQ_READ) >> LOCK_USAGE_READ_MASK;
	excl |= (excl & LOCKF_IRQ) << LOCK_USAGE_READ_MASK;

	return excl;
}

/*
 * Find the first pair of bit match between an original
 * usage mask and an exclusive usage mask.
 */
static int find_exclusive_match(unsigned long mask,
				unsigned long excl_mask,
				enum lock_usage_bit *bitp,
				enum lock_usage_bit *excl_bitp)
{
	int bit, excl, excl_read;

	for_each_set_bit(bit, &mask, LOCK_USED) {
		/*
		 * exclusive_bit() strips the read bit, however,
		 * LOCK_ENABLED_IRQ_*_READ may cause deadlocks too, so we need
		 * to search excl | LOCK_USAGE_READ_MASK as well.
		 */
		excl = exclusive_bit(bit);
		excl_read = excl | LOCK_USAGE_READ_MASK;
		if (excl_mask & lock_flag(excl)) {
			*bitp = bit;
			*excl_bitp = excl;
			return 0;
		} else if (excl_mask & lock_flag(excl_read)) {
			*bitp = bit;
			*excl_bitp = excl_read;
			return 0;
		}
	}
	return -1;
}

/*
 * Prove that the new dependency does not connect a hardirq-safe(-read)
 * lock with a hardirq-unsafe lock - to achieve this we search
 * the backwards-subgraph starting at <prev>, and the
 * forwards-subgraph starting at <next>:
 */
static int check_irq_usage(struct task_struct *curr, struct held_lock *prev,
			   struct held_lock *next)
{
	unsigned long usage_mask = 0, forward_mask, backward_mask;
	enum lock_usage_bit forward_bit = 0, backward_bit = 0;
	struct lock_list *target_entry1;
	struct lock_list *target_entry;
	struct lock_list this, that;
	enum bfs_result ret;

	/*
	 * Step 1: gather all hard/soft IRQs usages backward in an
	 * accumulated usage mask.
	 */
	bfs_init_rootb(&this, prev);

	ret = __bfs_backwards(&this, &usage_mask, usage_accumulate, usage_skip, NULL);
	if (bfs_error(ret)) {
		print_bfs_bug(ret);
		return 0;
	}

	usage_mask &= LOCKF_USED_IN_IRQ_ALL;
	if (!usage_mask)
		return 1;

	/*
	 * Step 2: find exclusive uses forward that match the previous
	 * backward accumulated mask.
	 */
	forward_mask = exclusive_mask(usage_mask);

	bfs_init_root(&that, next);

	ret = find_usage_forwards(&that, forward_mask, &target_entry1);
	if (bfs_error(ret)) {
		print_bfs_bug(ret);
		return 0;
	}
	if (ret == BFS_RNOMATCH)
		return 1;

	/*
	 * Step 3: we found a bad match! Now retrieve a lock from the backward
	 * list whose usage mask matches the exclusive usage mask from the
	 * lock found on the forward list.
	 *
	 * Note, we should only keep the LOCKF_ENABLED_IRQ_ALL bits, considering
	 * the follow case:
	 *
	 * When trying to add A -> B to the graph, we find that there is a
	 * hardirq-safe L, that L -> ... -> A, and another hardirq-unsafe M,
	 * that B -> ... -> M. However M is **softirq-safe**, if we use exact
	 * invert bits of M's usage_mask, we will find another lock N that is
	 * **softirq-unsafe** and N -> ... -> A, however N -> .. -> M will not
	 * cause a inversion deadlock.
	 */
	backward_mask = original_mask(target_entry1->class->usage_mask & LOCKF_ENABLED_IRQ_ALL);

	ret = find_usage_backwards(&this, backward_mask, &target_entry);
	if (bfs_error(ret)) {
		print_bfs_bug(ret);
		return 0;
	}
	if (DEBUG_LOCKS_WARN_ON(ret == BFS_RNOMATCH))
		return 1;

	/*
	 * Step 4: narrow down to a pair of incompatible usage bits
	 * and report it.
	 */
	ret = find_exclusive_match(target_entry->class->usage_mask,
				   target_entry1->class->usage_mask,
				   &backward_bit, &forward_bit);
	if (DEBUG_LOCKS_WARN_ON(ret == -1))
		return 1;

	print_bad_irq_dependency(curr, &this, &that,
				 target_entry, target_entry1,
				 prev, next,
				 backward_bit, forward_bit,
				 state_name(backward_bit));

	return 0;
}

#else

static inline int check_irq_usage(struct task_struct *curr,
				  struct held_lock *prev, struct held_lock *next)
{
	return 1;
}

static inline bool usage_skip(struct lock_list *entry, void *mask)
{
	return false;
}

#endif /* CONFIG_TRACE_IRQFLAGS */

#ifdef CONFIG_LOCKDEP_SMALL
/*
 * Check that the dependency graph starting at <src> can lead to
 * <target> or not. If it can, <src> -> <target> dependency is already
 * in the graph.
 *
 * Return BFS_RMATCH if it does, or BFS_RNOMATCH if it does not, return BFS_E* if
 * any error appears in the bfs search.
 */
static noinline enum bfs_result
check_redundant(struct held_lock *src, struct held_lock *target)
{
	enum bfs_result ret;
	struct lock_list *target_entry;
	struct lock_list src_entry;

	bfs_init_root(&src_entry, src);
	/*
	 * Special setup for check_redundant().
	 *
	 * To report redundant, we need to find a strong dependency path that
	 * is equal to or stronger than <src> -> <target>. So if <src> is E,
	 * we need to let __bfs() only search for a path starting at a -(E*)->,
	 * we achieve this by setting the initial node's ->only_xr to true in
	 * that case. And if <prev> is S, we set initial ->only_xr to false
	 * because both -(S*)-> (equal) and -(E*)-> (stronger) are redundant.
	 */
	src_entry.only_xr = src->read == 0;

	debug_atomic_inc(nr_redundant_checks);

	/*
	 * Note: we skip local_lock() for redundant check, because as the
	 * comment in usage_skip(), A -> local_lock() -> B and A -> B are not
	 * the same.
	 */
	ret = check_path(target, &src_entry, hlock_equal, usage_skip, &target_entry);

	if (ret == BFS_RMATCH)
		debug_atomic_inc(nr_redundant);

	return ret;
}

#else

static inline enum bfs_result
check_redundant(struct held_lock *src, struct held_lock *target)
{
	return BFS_RNOMATCH;
}

#endif

static void inc_chains(int irq_context)
{
	if (irq_context & LOCK_CHAIN_HARDIRQ_CONTEXT)
		nr_hardirq_chains++;
	else if (irq_context & LOCK_CHAIN_SOFTIRQ_CONTEXT)
		nr_softirq_chains++;
	else
		nr_process_chains++;
}

static void dec_chains(int irq_context)
{
	if (irq_context & LOCK_CHAIN_HARDIRQ_CONTEXT)
		nr_hardirq_chains--;
	else if (irq_context & LOCK_CHAIN_SOFTIRQ_CONTEXT)
		nr_softirq_chains--;
	else
		nr_process_chains--;
}

static void
print_deadlock_scenario(struct held_lock *nxt, struct held_lock *prv)
{
	struct lock_class *next = hlock_class(nxt);
	struct lock_class *prev = hlock_class(prv);

	printk(" Possible unsafe locking scenario:\n\n");
	printk("       CPU0\n");
	printk("       ----\n");
	printk("  lock(");
	__print_lock_name(prv, prev);
	printk(KERN_CONT ");\n");
	printk("  lock(");
	__print_lock_name(nxt, next);
	printk(KERN_CONT ");\n");
	printk("\n *** DEADLOCK ***\n\n");
	printk(" May be due to missing lock nesting notation\n\n");
}

static void
print_deadlock_bug(struct task_struct *curr, struct held_lock *prev,
		   struct held_lock *next)
{
	struct lock_class *class = hlock_class(prev);

	if (!debug_locks_off_graph_unlock() || debug_locks_silent)
		return;

	pr_warn("\n");
	pr_warn("============================================\n");
	pr_warn("WARNING: possible recursive locking detected\n");
	print_kernel_ident();
	pr_warn("--------------------------------------------\n");
	pr_warn("%s/%d is trying to acquire lock:\n",
		curr->comm, task_pid_nr(curr));
	print_lock(next);
	pr_warn("\nbut task is already holding lock:\n");
	print_lock(prev);

	if (class->cmp_fn) {
		pr_warn("and the lock comparison function returns %i:\n",
			class->cmp_fn(prev->instance, next->instance));
	}

	pr_warn("\nother info that might help us debug this:\n");
	print_deadlock_scenario(next, prev);
	lockdep_print_held_locks(curr);

	pr_warn("\nstack backtrace:\n");
	dump_stack();
}

/*
 * Check whether we are holding such a class already.
 *
 * (Note that this has to be done separately, because the graph cannot
 * detect such classes of deadlocks.)
 *
 * Returns: 0 on deadlock detected, 1 on OK, 2 if another lock with the same
 * lock class is held but nest_lock is also held, i.e. we rely on the
 * nest_lock to avoid the deadlock.
 */
static int
check_deadlock(struct task_struct *curr, struct held_lock *next)
{
	struct lock_class *class;
	struct held_lock *prev;
	struct held_lock *nest = NULL;
	int i;

	for (i = 0; i < curr->lockdep_depth; i++) {
		prev = curr->held_locks + i;

		if (prev->instance == next->nest_lock)
			nest = prev;

		if (hlock_class(prev) != hlock_class(next))
			continue;

		/*
		 * Allow read-after-read recursion of the same
		 * lock class (i.e. read_lock(lock)+read_lock(lock)):
		 */
		if ((next->read == 2) && prev->read)
			continue;

		class = hlock_class(prev);

		if (class->cmp_fn &&
		    class->cmp_fn(prev->instance, next->instance) < 0)
			continue;

		/*
		 * We're holding the nest_lock, which serializes this lock's
		 * nesting behaviour.
		 */
		if (nest)
			return 2;

		print_deadlock_bug(curr, prev, next);
		return 0;
	}
	return 1;
}

/*
 * There was a chain-cache miss, and we are about to add a new dependency
 * to a previous lock. We validate the following rules:
 *
 *  - would the adding of the <prev> -> <next> dependency create a
 *    circular dependency in the graph? [== circular deadlock]
 *
 *  - does the new prev->next dependency connect any hardirq-safe lock
 *    (in the full backwards-subgraph starting at <prev>) with any
 *    hardirq-unsafe lock (in the full forwards-subgraph starting at
 *    <next>)? [== illegal lock inversion with hardirq contexts]
 *
 *  - does the new prev->next dependency connect any softirq-safe lock
 *    (in the full backwards-subgraph starting at <prev>) with any
 *    softirq-unsafe lock (in the full forwards-subgraph starting at
 *    <next>)? [== illegal lock inversion with softirq contexts]
 *
 * any of these scenarios could lead to a deadlock.
 *
 * Then if all the validations pass, we add the forwards and backwards
 * dependency.
 */
static int
check_prev_add(struct task_struct *curr, struct held_lock *prev,
	       struct held_lock *next, u16 distance,
	       struct lock_trace **const trace)
{
	struct lock_list *entry;
	enum bfs_result ret;

	if (!hlock_class(prev)->key || !hlock_class(next)->key) {
		/*
		 * The warning statements below may trigger a use-after-free
		 * of the class name. It is better to trigger a use-after free
		 * and to have the class name most of the time instead of not
		 * having the class name available.
		 */
		WARN_ONCE(!debug_locks_silent && !hlock_class(prev)->key,
			  "Detected use-after-free of lock class %px/%s\n",
			  hlock_class(prev),
			  hlock_class(prev)->name);
		WARN_ONCE(!debug_locks_silent && !hlock_class(next)->key,
			  "Detected use-after-free of lock class %px/%s\n",
			  hlock_class(next),
			  hlock_class(next)->name);
		return 2;
	}

	if (prev->class_idx == next->class_idx) {
		struct lock_class *class = hlock_class(prev);

		if (class->cmp_fn &&
		    class->cmp_fn(prev->instance, next->instance) < 0)
			return 2;
	}

	/*
	 * Prove that the new <prev> -> <next> dependency would not
	 * create a circular dependency in the graph. (We do this by
	 * a breadth-first search into the graph starting at <next>,
	 * and check whether we can reach <prev>.)
	 *
	 * The search is limited by the size of the circular queue (i.e.,
	 * MAX_CIRCULAR_QUEUE_SIZE) which keeps track of a breadth of nodes
	 * in the graph whose neighbours are to be checked.
	 */
	ret = check_noncircular(next, prev, trace);
	if (unlikely(bfs_error(ret) || ret == BFS_RMATCH))
		return 0;

	if (!check_irq_usage(curr, prev, next))
		return 0;

	/*
	 * Is the <prev> -> <next> dependency already present?
	 *
	 * (this may occur even though this is a new chain: consider
	 *  e.g. the L1 -> L2 -> L3 -> L4 and the L5 -> L1 -> L2 -> L3
	 *  chains - the second one will be new, but L1 already has
	 *  L2 added to its dependency list, due to the first chain.)
	 */
	list_for_each_entry(entry, &hlock_class(prev)->locks_after, entry) {
		if (entry->class == hlock_class(next)) {
			if (distance == 1)
				entry->distance = 1;
			entry->dep |= calc_dep(prev, next);

			/*
			 * Also, update the reverse dependency in @next's
			 * ->locks_before list.
			 *
			 *  Here we reuse @entry as the cursor, which is fine
			 *  because we won't go to the next iteration of the
			 *  outer loop:
			 *
			 *  For normal cases, we return in the inner loop.
			 *
			 *  If we fail to return, we have inconsistency, i.e.
			 *  <prev>::locks_after contains <next> while
			 *  <next>::locks_before doesn't contain <prev>. In
			 *  that case, we return after the inner and indicate
			 *  something is wrong.
			 */
			list_for_each_entry(entry, &hlock_class(next)->locks_before, entry) {
				if (entry->class == hlock_class(prev)) {
					if (distance == 1)
						entry->distance = 1;
					entry->dep |= calc_depb(prev, next);
					return 1;
				}
			}

			/* <prev> is not found in <next>::locks_before */
			return 0;
		}
	}

	/*
	 * Is the <prev> -> <next> link redundant?
	 */
	ret = check_redundant(prev, next);
	if (bfs_error(ret))
		return 0;
	else if (ret == BFS_RMATCH)
		return 2;

	if (!*trace) {
		*trace = save_trace();
		if (!*trace)
			return 0;
	}

	/*
	 * Ok, all validations passed, add the new lock
	 * to the previous lock's dependency list:
	 */
	ret = add_lock_to_list(hlock_class(next), hlock_class(prev),
			       &hlock_class(prev)->locks_after, distance,
			       calc_dep(prev, next), *trace);

	if (!ret)
		return 0;

	ret = add_lock_to_list(hlock_class(prev), hlock_class(next),
			       &hlock_class(next)->locks_before, distance,
			       calc_depb(prev, next), *trace);
	if (!ret)
		return 0;

	return 2;
}

/*
 * Add the dependency to all directly-previous locks that are 'relevant'.
 * The ones that are relevant are (in increasing distance from curr):
 * all consecutive trylock entries and the final non-trylock entry - or
 * the end of this context's lock-chain - whichever comes first.
 */
static int
check_prevs_add(struct task_struct *curr, struct held_lock *next)
{
	struct lock_trace *trace = NULL;
	int depth = curr->lockdep_depth;
	struct held_lock *hlock;

	/*
	 * Debugging checks.
	 *
	 * Depth must not be zero for a non-head lock:
	 */
	if (!depth)
		goto out_bug;
	/*
	 * At least two relevant locks must exist for this
	 * to be a head:
	 */
	if (curr->held_locks[depth].irq_context !=
			curr->held_locks[depth-1].irq_context)
		goto out_bug;

	for (;;) {
		u16 distance = curr->lockdep_depth - depth + 1;
		hlock = curr->held_locks + depth - 1;

		if (hlock->check) {
			int ret = check_prev_add(curr, hlock, next, distance, &trace);
			if (!ret)
				return 0;

			/*
			 * Stop after the first non-trylock entry,
			 * as non-trylock entries have added their
			 * own direct dependencies already, so this
			 * lock is connected to them indirectly:
			 */
			if (!hlock->trylock)
				break;
		}

		depth--;
		/*
		 * End of lock-stack?
		 */
		if (!depth)
			break;
		/*
		 * Stop the search if we cross into another context:
		 */
		if (curr->held_locks[depth].irq_context !=
				curr->held_locks[depth-1].irq_context)
			break;
	}
	return 1;
out_bug:
	if (!debug_locks_off_graph_unlock())
		return 0;

	/*
	 * Clearly we all shouldn't be here, but since we made it we
	 * can reliable say we messed up our state. See the above two
	 * gotos for reasons why we could possibly end up here.
	 */
	WARN_ON(1);

	return 0;
}

struct lock_chain lock_chains[MAX_LOCKDEP_CHAINS];
static DECLARE_BITMAP(lock_chains_in_use, MAX_LOCKDEP_CHAINS);
static u16 chain_hlocks[MAX_LOCKDEP_CHAIN_HLOCKS];
unsigned long nr_zapped_lock_chains;
unsigned int nr_free_chain_hlocks;	/* Free chain_hlocks in buckets */
unsigned int nr_lost_chain_hlocks;	/* Lost chain_hlocks */
unsigned int nr_large_chain_blocks;	/* size > MAX_CHAIN_BUCKETS */

/*
 * The first 2 chain_hlocks entries in the chain block in the bucket
 * list contains the following meta data:
 *
 *   entry[0]:
 *     Bit    15 - always set to 1 (it is not a class index)
 *     Bits 0-14 - upper 15 bits of the next block index
 *   entry[1]    - lower 16 bits of next block index
 *
 * A next block index of all 1 bits means it is the end of the list.
 *
 * On the unsized bucket (bucket-0), the 3rd and 4th entries contain
 * the chain block size:
 *
 *   entry[2] - upper 16 bits of the chain block size
 *   entry[3] - lower 16 bits of the chain block size
 */
#define MAX_CHAIN_BUCKETS	16
#define CHAIN_BLK_FLAG		(1U << 15)
#define CHAIN_BLK_LIST_END	0xFFFFU

static int chain_block_buckets[MAX_CHAIN_BUCKETS];

static inline int size_to_bucket(int size)
{
	if (size > MAX_CHAIN_BUCKETS)
		return 0;

	return size - 1;
}

/*
 * Iterate all the chain blocks in a bucket.