// 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__
/*
 * Check if an address is part of freed initmem. After initmem is freed,
 * memory can be allocated from it, and such allocations would then have
 * addresses within the range [_stext, _end].
 */
#ifndef arch_is_kernel_initmem_freed
static int arch_is_kernel_initmem_freed(unsigned long addr)
{
        if (system_state < SYSTEM_FREEING_INITMEM)
                return 0;

        return init_section_contains((void *)addr, 1);
}
#endif

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;

        /*
         * 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_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);
        }

        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;
}

/*
 * 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();
                }

                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)
{
        /*
         * 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) {
                if (DEBUG_LOCKS_WARN_ON(entry->class->wait_type_inner < LD_WAIT_CONFIG))
                        return false;

                return true;
        }

        return false;
}

/*
 * 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(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(safe_class);
                printk(KERN_CONT " --> ");
                __print_lock_name(middle_class);
                printk(KERN_CONT " --> ");
                __print_lock_name(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(unsafe_class);
        printk(KERN_CONT ");\n");
        printk("                               local_irq_disable();\n");
        printk("                               lock(");
        __print_lock_name(safe_class);
        printk(KERN_CONT ");\n");
        printk("                               lock(");
        __print_lock_name(middle_class);
        printk(KERN_CONT ");\n");
        printk("  <Interrupt>\n");
        printk("    lock(");
        __print_lock_name(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(hlock_class(prev));
        pr_cont(" ->");
        print_lock_name(hlock_class(next));
        pr_cont("\n");

        pr_warn("\nbut this new dependency connects a %s-irq-safe lock:\n",
                irqclass);
        print_lock_name(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(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(prev);
        printk(KERN_CONT ");\n");
        printk("  lock(");
        __print_lock_name(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)
{
        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);

        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 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;

                /*
                 * 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;
        }

        /*
         * 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,
                               next->acquire_ip, 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,
                               next->acquire_ip, 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.
 */
#define for_each_chain_block(bucket, prev, curr)                \
        for ((prev) = -1, (curr) = chain_block_buckets[bucket]; \
             (curr) >= 0;                                       \
             (prev) = (curr), (curr) = chain_block_next(curr))

/*
 * next block or -1
 */
static inline int chain_block_next(int offset)
{
        int next = chain_hlocks[offset];

        WARN_ON_ONCE(!(next & CHAIN_BLK_FLAG));

        if (next == CHAIN_BLK_LIST_END)
                return -1;

        next &= ~CHAIN_BLK_FLAG;
        next <<= 16;
        next |= chain_hlocks[offset + 1];

        return next;
}

/*
 * bucket-0 only
 */
static inline int chain_block_size(int offset)
{
        return (chain_hlocks[offset + 2] << 16) | chain_hlocks[offset + 3];
}

static inline void init_chain_block(int offset, int next, int bucket, int size)
{
        chain_hlocks[offset] = (next >> 16) | CHAIN_BLK_FLAG;
        chain_hlocks[offset + 1] = (u16)next;

        if (size && !bucket) {
                chain_hlocks[offset + 2] = size >> 16;
                chain_hlocks[offset + 3] = (u16)size;
        }
}

static inline void add_chain_block(int offset, int size)
{
        int bucket = size_to_bucket(size);
        int next = chain_block_buckets[bucket];
        int prev, curr;

        if (unlikely(size < 2)) {
                /*
                 * We can't store single entries on the freelist. Leak them.
                 *
                 * One possible way out would be to uniquely mark them, other
                 * than with CHAIN_BLK_FLAG, such that we can recover them when
                 * the block before it is re-added.
                 */
                if (size)
                        nr_lost_chain_hlocks++;
                return;
        }

        nr_free_chain_hlocks += size;
        if (!bucket) {
                nr_large_chain_blocks++;

                /*
                 * Variable sized, sort large to small.
                 */
                for_each_chain_block(0, prev, curr) {
                        if (size >= chain_block_size(curr))
                                break;
                }
                init_chain_block(offset, curr, 0, size);
                if (prev < 0)
                        chain_block_buckets[0] = offset;
                else
                        init_chain_block(prev, offset, 0, 0);
                return;
        }
        /*
         * Fixed size, add to head.
         */
        init_chain_block(offset, next, bucket, size);
        chain_block_buckets[bucket] = offset;
}

/*
 * Only the first block in the list can be deleted.
 *
 * For the variable size bucket[0], the first block (the largest one) is
 * returned, broken up and put back into the pool. So if a chain block of
 * length > MAX_CHAIN_BUCKETS is ever used and zapped, it will just be
 * queued up after the primordial chain block and never be used until the
 * hlock entries in the primordial chain block is almost used up. That
 * causes fragmentation and reduce allocation efficiency. That can be
 * monitored by looking at the "large chain blocks" number in lockdep_stats.
 */
static inline void del_chain_block(int bucket, int size, int next)
{
        nr_free_chain_hlocks -= size;
        chain_block_buckets[bucket] = next;

        if (!bucket)
                nr_large_chain_blocks--;
}

static void init_chain_block_buckets(void)
{
        int i;

        for (i = 0; i < MAX_CHAIN_BUCKETS; i++)
                chain_block_buckets[i] = -1;

        add_chain_block(0, ARRAY_SIZE(chain_hlocks));
}

/*
 * Return offset of a chain block of the right size or -1 if not found.
 *
 * Fairly simple worst-fit allocator with the addition of a number of size
 * specific free lists.
 */
static int alloc_chain_hlocks(int req)
{
        int bucket, curr, size;

        /*
         * We rely on the MSB to act as an escape bit to denote freelist
         * pointers. Make sure this bit isn't set in 'normal' class_idx usage.
         */
        BUILD_BUG_ON((MAX_LOCKDEP_KEYS-1) & CHAIN_BLK_FLAG);

        init_data_structures_once();

        if (nr_free_chain_hlocks < req)
                return -1;

        /*
         * We require a minimum of 2 (u16) entries to encode a freelist
         * 'pointer'.
         */
        req = max(req, 2);
        bucket = size_to_bucket(req);
        curr = chain_block_buckets[bucket];

        if (bucket) {
                if (curr >= 0) {
                        del_chain_block(bucket, req, chain_block_next(curr));
                        return curr;
                }
                /* Try bucket 0 */
                curr = chain_block_buckets[0];
        }

        /*
         * The variable sized freelist is sorted by size; the first entry is
         * the largest. Use it if it fits.
         */
        if (curr >= 0) {
                size = chain_block_size(curr);
                if (likely(size >= req)) {
                        del_chain_block(0, size, chain_block_next(curr));
                        add_chain_block(curr + req, size - req);
                        return curr;
                }
        }

        /*
         * Last resort, split a block in a larger sized bucket.
         */
        for (size = MAX_CHAIN_BUCKETS; size > req; size--) {
                bucket = size_to_bucket(size);
                curr = chain_block_buckets[bucket];
                if (curr < 0)
                        continue;

                del_chain_block(bucket, size, chain_block_next(curr));
                add_chain_block(curr + req, size - req);
                return curr;
        }

        return -1;
}

static inline void free_chain_hlocks(int base, int size)
{
        add_chain_block(base, max(size, 2));
}

struct lock_class *lock_chain_get_class(struct lock_chain *chain, int i)
{
        u16 chain_hlock = chain_hlocks[chain->base + i];
        unsigned int class_idx = chain_hlock_class_idx(chain_hlock);

        return lock_classes + class_idx;
}

/*
 * Returns the index of the first held_lock of the current chain
 */
static inline int get_first_held_lock(struct task_struct *curr,
                                        struct held_lock *hlock)
{
        int i;
        struct held_lock *hlock_curr;

        for (i = curr->lockdep_depth - 1; i >= 0; i--) {
                hlock_curr = curr->held_locks + i;
                if (hlock_curr->irq_context != hlock->irq_context)
                        break;

        }

        return ++i;
}

#ifdef CONFIG_DEBUG_LOCKDEP
/*
 * Returns the next chain_key iteration
 */
static u64 print_chain_key_iteration(u16 hlock_id, u64 chain_key)
{
        u64 new_chain_key = iterate_chain_key(chain_key, hlock_id);

        printk(" hlock_id:%d -> chain_key:%016Lx",
                (unsigned int)hlock_id,
                (unsigned long long)new_chain_key);
        return new_chain_key;
}

static void
print_chain_keys_held_locks(struct task_struct *curr, struct held_lock *hlock_next)
{
        struct held_lock *hlock;
        u64 chain_key = INITIAL_CHAIN_KEY;
        int depth = curr->lockdep_depth;
        int i = get_first_held_lock(curr, hlock_next);

        printk("depth: %u (irq_context %u)\n", depth - i + 1,
                hlock_next->irq_context);
        for (; i < depth; i++) {
                hlock = curr->held_locks + i;
                chain_key = print_chain_key_iteration(hlock_id(hlock), chain_key);

                print_lock(hlock);
        }

        print_chain_key_iteration(hlock_id(hlock_next), chain_key);
        print_lock(hlock_next);
}

static void print_chain_keys_chain(struct lock_chain *chain)
{
        int i;
        u64 chain_key = INITIAL_CHAIN_KEY;
        u16 hlock_id;

        printk("depth: %u\n", chain->depth);
        for (i = 0; i < chain->depth; i++) {
                hlock_id = chain_hlocks[chain->base + i];
                chain_key = print_chain_key_iteration(hlock_id, chain_key);

                print_lock_name(lock_classes + chain_hlock_class_idx(hlock_id));
                printk("\n");
        }
}

static void print_collision(struct task_struct *curr,
                        struct held_lock *hlock_next,
                        struct lock_chain *chain)
{
        pr_warn("\n");
        pr_warn("============================\n");
        pr_warn("WARNING: chain_key collision\n");
        print_kernel_ident();
        pr_warn("----------------------------\n");
        pr_warn("%s/%d: ", current->comm, task_pid_nr(current));
        pr_warn("Hash chain already cached but the contents don't match!\n");

        pr_warn("Held locks:");
        print_chain_keys_held_locks(curr, hlock_next);

        pr_warn("Locks in cached chain:");
        print_chain_keys_chain(chain);

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

/*
 * Checks whether the chain and the current held locks are consistent
 * in depth and also in content. If they are not it most likely means
 * that there was a collision during the calculation of the chain_key.
 * Returns: 0 not passed, 1 passed
 */
static int check_no_collision(struct task_struct *curr,
                        struct held_lock *hlock,
                        struct lock_chain *chain)
{
#ifdef CONFIG_DEBUG_LOCKDEP
        int i, j, id;

        i = get_first_held_lock(curr, hlock);

        if (DEBUG_LOCKS_WARN_ON(chain->depth != curr->lockdep_depth - (i - 1))) {
                print_collision(curr, hlock, chain);
                return 0;
        }

        for (j = 0; j < chain->depth - 1; j++, i++) {
                id = hlock_id(&curr->held_locks[i]);

                if (DEBUG_LOCKS_WARN_ON(chain_hlocks[chain->base + j] != id)) {
                        print_collision(curr, hlock, chain);
                        return 0;
                }
        }
#endif
        return 1;
}

/*
 * Given an index that is >= -1, return the index of the next lock chain.
 * Return -2 if there is no next lock chain.
 */
long lockdep_next_lockchain(long i)
{
        i = find_next_bit(lock_chains_in_use, ARRAY_SIZE(lock_chains), i + 1);
        return i < ARRAY_SIZE(lock_chains) ? i : -2;
}

unsigned long lock_chain_count(void)
{
        return bitmap_weight(lock_chains_in_use, ARRAY_SIZE(lock_chains));
}

/* Must be called with the graph lock held. */
static struct lock_chain *alloc_lock_chain(void)
{
        int idx = find_first_zero_bit(lock_chains_in_use,
                                      ARRAY_SIZE(lock_chains));

        if (unlikely(idx >= ARRAY_SIZE(lock_chains)))
                return NULL;
        __set_bit(idx, lock_chains_in_use);
        return lock_chains + idx;
}

/*
 * Adds a dependency chain into chain hashtable. And must be called with
 * graph_lock held.
 *
 * Return 0 if fail, and graph_lock is released.
 * Return 1 if succeed, with graph_lock held.
 */
static inline int add_chain_cache(struct task_struct *curr,
                                  struct held_lock *hlock,
                                  u64 chain_key)
{
        struct hlist_head *hash_head = chainhashentry(chain_key);
        struct lock_chain *chain;
        int i, j;

        /*
         * The caller must hold the graph lock, ensure we've got IRQs
         * disabled to make this an IRQ-safe lock.. for recursion reasons
         * lockdep won't complain about its own locking errors.
         */
        if (lockdep_assert_locked())
                return 0;

        chain = alloc_lock_chain();
        if (!chain) {
                if (!debug_locks_off_graph_unlock())
                        return 0;

                print_lockdep_off("BUG: MAX_LOCKDEP_CHAINS too low!");
                dump_stack();
                return 0;
        }
        chain->chain_key = chain_key;
        chain->irq_context = hlock->irq_context;
        i = get_first_held_lock(curr, hlock);
        chain->depth = curr->lockdep_depth + 1 - i;

        BUILD_BUG_ON((1UL << 24) <= ARRAY_SIZE(chain_hlocks));
        BUILD_BUG_ON((1UL << 6)  <= ARRAY_SIZE(curr->held_locks));
        BUILD_BUG_ON((1UL << 8*sizeof(chain_hlocks[0])) <= ARRAY_SIZE(lock_classes));

        j = alloc_chain_hlocks(chain->depth);
        if (j < 0) {
                if (!debug_locks_off_graph_unlock())
                        return 0;

                print_lockdep_off("BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!");
                dump_stack();
                return 0;
        }

        chain->base = j;
        for (j = 0; j < chain->depth - 1; j++, i++) {
                int lock_id = hlock_id(curr->held_locks + i);

                chain_hlocks[chain->base + j] = lock_id;
        }
        chain_hlocks[chain->base + j] = hlock_id(hlock);
        hlist_add_head_rcu(&chain->entry, hash_head);
        debug_atomic_inc(chain_lookup_misses);
        inc_chains(chain->irq_context);

        return 1;
}

/*
 * Look up a dependency chain. Must be called with either the graph lock or
 * the RCU read lock held.
 */
static inline struct lock_chain *lookup_chain_cache(u64 chain_key)
{
        struct hlist_head *hash_head = chainhashentry(chain_key);
        struct lock_chain *chain;

        hlist_for_each_entry_rcu(chain, hash_head, entry) {
                if (READ_ONCE(chain->chain_key) == chain_key) {
                        debug_atomic_inc(chain_lookup_hits);
                        return chain;
                }
        }
        return NULL;
}

/*
 * If the key is not present yet in dependency chain cache then
 * add it and return 1 - in this case the new dependency chain is
 * validated. If the key is already hashed, return 0.
 * (On return with 1 graph_lock is held.)
 */
static inline int lookup_chain_cache_add(struct task_struct *curr,
                                         struct held_lock *hlock,
                                         u64 chain_key)
{
        struct lock_class *class = hlock_class(hlock);
        struct lock_chain *chain = lookup_chain_cache(chain_key);

        if (chain) {
cache_hit:
                if (!check_no_collision(curr, hlock, chain))
                        return 0;

                if (very_verbose(class)) {
                        printk("\nhash chain already cached, key: "
                                        "%016Lx tail class: [%px] %s\n",
                                        (unsigned long long)chain_key,
                                        class->key, class->name);
                }

                return 0;
        }

        if (very_verbose(class)) {
                printk("\nnew hash chain, key: %016Lx tail class: [%px] %s\n",
                        (unsigned long long)chain_key, class->key, class->name);
        }

        if (!graph_lock())
                return 0;

        /*
         * We have to walk the chain again locked - to avoid duplicates:
         */
        chain = lookup_chain_cache(chain_key);
        if (chain) {
                graph_unlock();
                goto cache_hit;
        }

        if (!add_chain_cache(curr, hlock, chain_key))
                return 0;

        return 1;
}

static int validate_chain(struct task_struct *curr,
                          struct held_lock *hlock,
                          int chain_head, u64 chain_key)
{
        /*
         * Trylock needs to maintain the stack of held locks, but it
         * does not add new dependencies, because trylock can be done
         * in any order.
         *
         * We look up the chain_key and do the O(N^2) check and update of
         * the dependencies only if this is a new dependency chain.
         * (If lookup_chain_cache_add() return with 1 it acquires
         * graph_lock for us)
         */
        if (!hlock->trylock && hlock->check &&
            lookup_chain_cache_add(curr, hlock, chain_key)) {
                /*
                 * Check whether last held lock:
                 *
                 * - is irq-safe, if this lock is irq-unsafe
                 * - is softirq-safe, if this lock is hardirq-unsafe
                 *
                 * And check whether the new lock's dependency graph
                 * could lead back to the previous lock:
                 *
                 * - within the current held-lock stack
                 * - across our accumulated lock dependency records
                 *
                 * any of these scenarios could lead to a deadlock.
                 */
                /*
                 * The simple case: does the current hold the same lock
                 * already?
                 */
                int ret = check_deadlock(curr, hlock);

                if (!ret)
                        return 0;
                /*
                 * Add dependency only if this lock is not the head
                 * of the chain, and if the new lock introduces no more
                 * lock dependency (because we already hold a lock with the
                 * same lock class) nor deadlock (because the nest_lock
                 * serializes nesting locks), see the comments for
                 * check_deadlock().
                 */
                if (!chain_head && ret != 2) {
                        if (!check_prevs_add(curr, hlock))
                                return 0;
                }

                graph_unlock();
        } else {
                /* after lookup_chain_cache_add(): */
                if (unlikely(!debug_locks))
                        return 0;
        }

        return 1;
}
#else
static inline int validate_chain(struct task_struct *curr,
                                 struct held_lock *hlock,
                                 int chain_head, u64 chain_key)
{
        return 1;
}

static void init_chain_block_buckets(void)      { }
#endif /* CONFIG_PROVE_LOCKING */

/*
 * We are building curr_chain_key incrementally, so double-check
 * it from scratch, to make sure that it's done correctly:
 */
static void check_chain_key(struct task_struct *curr)
{
#ifdef CONFIG_DEBUG_LOCKDEP
        struct held_lock *hlock, *prev_hlock = NULL;
        unsigned int i;
        u64 chain_key = INITIAL_CHAIN_KEY;

        for (i = 0; i < curr->lockdep_depth; i++) {
                hlock = curr->held_locks + i;
                if (chain_key != hlock->prev_chain_key) {
                        debug_locks_off();
                        /*
                         * We got mighty confused, our chain keys don't match
                         * with what we expect, someone trample on our task state?
                         */
                        WARN(1, "hm#1, depth: %u [%u], %016Lx != %016Lx\n",
                                curr->lockdep_depth, i,
                                (unsigned long long)chain_key,
                                (unsigned long long)hlock->prev_chain_key);
                        return;
                }

                /*
                 * hlock->class_idx can't go beyond MAX_LOCKDEP_KEYS, but is
                 * it registered lock class index?
                 */
                if (DEBUG_LOCKS_WARN_ON(!test_bit(hlock->class_idx, lock_classes_in_use)))
                        return;

                if (prev_hlock && (prev_hlock->irq_context !=
                                                        hlock->irq_context))
                        chain_key = INITIAL_CHAIN_KEY;
                chain_key = iterate_chain_key(chain_key, hlock_id(hlock));
                prev_hlock = hlock;
        }
        if (chain_key != curr->curr_chain_key) {
                debug_locks_off();
                /*
                 * More smoking hash instead of calculating it, damn see these
                 * numbers float.. I bet that a pink elephant stepped on my memory.
                 */
                WARN(1, "hm#2, depth: %u [%u], %016Lx != %016Lx\n",
                        curr->lockdep_depth, i,
                        (unsigned long long)chain_key,
                        (unsigned long long)curr->curr_chain_key);
        }
#endif
}

#ifdef CONFIG_PROVE_LOCKING
static int mark_lock(struct task_struct *curr, struct held_lock *this,
                     enum lock_usage_bit new_bit);

static void print_usage_bug_scenario(struct held_lock *lock)
{
        struct lock_class *class = hlock_class(lock);

        printk(" Possible unsafe locking scenario:\n\n");
        printk("       CPU0\n");
        printk("       ----\n");
        printk("  lock(");
        __print_lock_name(class);
        printk(KERN_CONT ");\n");
        printk("  <Interrupt>\n");
        printk("    lock(");
        __print_lock_name(class);
        printk(KERN_CONT ");\n");
        printk("\n *** DEADLOCK ***\n\n");
}

static void
print_usage_bug(struct task_struct *curr, struct held_lock *this,
                enum lock_usage_bit prev_bit, enum lock_usage_bit new_bit)
{
        if (!debug_locks_off() || debug_locks_silent)
                return;

        pr_warn("\n");
        pr_warn("================================\n");
        pr_warn("WARNING: inconsistent lock state\n");
        print_kernel_ident();
        pr_warn("--------------------------------\n");

        pr_warn("inconsistent {%s} -> {%s} usage.\n",
                usage_str[prev_bit], usage_str[new_bit]);

        pr_warn("%s/%d [HC%u[%lu]:SC%u[%lu]:HE%u:SE%u] takes:\n",
                curr->comm, task_pid_nr(curr),
                lockdep_hardirq_context(), hardirq_count() >> HARDIRQ_SHIFT,
                lockdep_softirq_context(curr), softirq_count() >> SOFTIRQ_SHIFT,
                lockdep_hardirqs_enabled(),
                lockdep_softirqs_enabled(curr));
        print_lock(this);

        pr_warn("{%s} state was registered at:\n", usage_str[prev_bit]);
        print_lock_trace(hlock_class(this)->usage_traces[prev_bit], 1);

        print_irqtrace_events(curr);
        pr_warn("\nother info that might help us debug this:\n");
        print_usage_bug_scenario(this);

        lockdep_print_held_locks(curr);

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

/*
 * Print out an error if an invalid bit is set:
 */
static inline int
valid_state(struct task_struct *curr, struct held_lock *this,
            enum lock_usage_bit new_bit, enum lock_usage_bit bad_bit)
{
        if (unlikely(hlock_class(this)->usage_mask & (1 << bad_bit))) {
                graph_unlock();
                print_usage_bug(curr, this, bad_bit, new_bit);
                return 0;
        }
        return 1;
}


/*
 * print irq inversion bug:
 */
static void
print_irq_inversion_bug(struct task_struct *curr,
                        struct lock_list *root, struct lock_list *other,
                        struct held_lock *this, int forwards,
                        const char *irqclass)
{
        struct lock_list *entry = other;
        struct lock_list *middle = NULL;
        int depth;

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

        pr_warn("\n");
        pr_warn("========================================================\n");
        pr_warn("WARNING: possible irq lock inversion dependency detected\n");
        print_kernel_ident();
        pr_warn("--------------------------------------------------------\n");
        pr_warn("%s/%d just changed the state of lock:\n",
                curr->comm, task_pid_nr(curr));
        print_lock(this);
        if (forwards)
                pr_warn("but this lock took another, %s-unsafe lock in the past:\n", irqclass);
        else
                pr_warn("but this lock was taken by another, %s-safe lock in the past:\n", irqclass);
        print_lock_name(other->class);
        pr_warn("\n\nand interrupts could create inverse lock ordering between them.\n\n");

        pr_warn("\nother info that might help us debug this:\n");

        /* Find a middle lock (if one exists) */
        depth = get_lock_depth(other);
        do {
                if (depth == 0 && (entry != root)) {
                        pr_warn("lockdep:%s bad path found in chain graph\n", __func__);
                        break;
                }
                middle = entry;
                entry = get_lock_parent(entry);
                depth--;
        } while (entry && entry != root && (depth >= 0));
        if (forwards)
                print_irq_lock_scenario(root, other,
                        middle ? middle->class : root->class, other->class);
        else
                print_irq_lock_scenario(other, root,