// 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 <asm/sections.h>

#include "lockdep_internals.h"

#define CREATE_TRACE_POINTS
#include <trace/events/lock.h>

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

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

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;
#ifndef CONFIG_DEBUG_LOCKDEP
static
#endif
struct lock_class lock_classes[MAX_LOCKDEP_KEYS];
static 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.
 */
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 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);
        }
}

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

        get_usage_chars(class, usage);

        printk(KERN_CONT " (");
        __print_lock_name(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(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 start = (unsigned long) &_stext,
                      end   = (unsigned long) &_end,
                      addr  = (unsigned long) obj;

        if (arch_is_kernel_initmem_freed(addr))
                return 0;

        /*
         * static variable?
         */
        if ((addr >= start) && (addr < end))
                return 1;

        if (arch_is_kernel_data(addr))
                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(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_ON_ONCE(class->name != lock->name &&
                                     lock->key != &__lockdep_no_validate__);
                        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;

        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);

        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,
                            unsigned long ip, 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(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;

        /*
         * 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(source);
                printk(KERN_CONT " --> ");
                __print_lock_name(parent);
                printk(KERN_CONT " --> ");
                __print_lock_name(target);
                printk(KERN_CONT "\n\n");
        }

        printk(" Possible unsafe locking scenario:\n\n");
        printk("       CPU0                    CPU1\n");
        printk("       ----                    ----\n");
        printk("  lock(");
        __print_lock_name(target);
        printk(KERN_CONT ");\n");
        printk("                               lock(");
        __print_lock_name(parent);
        printk(KERN_CONT ");\n");
        printk("                               lock(");
        __print_lock_name(target);
        printk(KERN_CONT ");\n");
        printk("  lock(");
        __print_lock_name(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);
        }