Merge tag 'perf-core-for-mingo-5.1-20190225' of git://git.kernel.org/pub/scm/linux...

[muen/linux.git] / kernel / locking / lockdep.c

/*
 * 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/bitops.h>
#include <linux/gfp.h>
#include <linux/random.h>
#include <linux/jhash.h>
#include <linux/nmi.h>
#include <linux/kprobes.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

/*
 * 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 lockdep_lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;

static int graph_lock(void)
{
        arch_spin_lock(&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) {
                arch_spin_unlock(&lockdep_lock);
                return 0;
        }
        /* prevent any recursions within lockdep from causing deadlocks */
        current->lockdep_recursion++;
        return 1;
}

static inline int graph_unlock(void)
{
        if (debug_locks && !arch_spin_is_locked(&lockdep_lock)) {
                /*
                 * The lockdep graph lock isn't locked while we expect it to
                 * be, we're confused now, bye!
                 */
                return DEBUG_LOCKS_WARN_ON(1);
        }

        current->lockdep_recursion--;
        arch_spin_unlock(&lockdep_lock);
        return 0;
}

/*
 * 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();

        arch_spin_unlock(&lockdep_lock);

        return ret;
}

unsigned long nr_list_entries;
static struct lock_list list_entries[MAX_LOCKDEP_ENTRIES];

/*
 * All data structures here are protected by the global debug_lock.
 *
 * Mutex key structs only get allocated, once during bootup, and never
 * get freed - this significantly simplifies the debugging code.
 */
unsigned long nr_lock_classes;
#ifndef CONFIG_DEBUG_LOCKDEP
static
#endif
struct lock_class lock_classes[MAX_LOCKDEP_KEYS];

static inline struct lock_class *hlock_class(struct held_lock *hlock)
{
        if (!hlock->class_idx) {
                /*
                 * Someone passed in garbage, we give up.
                 */
                DEBUG_LOCKS_WARN_ON(1);
                return NULL;
        }
        return lock_classes + hlock->class_idx - 1;
}

#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 only grows,
 * never shrinks. The list is only accessed with the lockdep
 * spinlock lock held.
 */
LIST_HEAD(all_lock_classes);

/*
 * 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 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_off(void)
{
        current->lockdep_recursion++;
}
EXPORT_SYMBOL(lockdep_off);

void lockdep_on(void)
{
        current->lockdep_recursion--;
}
EXPORT_SYMBOL(lockdep_on);

/*
 * 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;
}

/*
 * Stack-trace: tightly packed array of stack backtrace
 * addresses. Protected by the graph_lock.
 */
unsigned long nr_stack_trace_entries;
static unsigned long stack_trace[MAX_STACK_TRACE_ENTRIES];

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
}

static int save_trace(struct stack_trace *trace)
{
        trace->nr_entries = 0;
        trace->max_entries = MAX_STACK_TRACE_ENTRIES - nr_stack_trace_entries;
        trace->entries = stack_trace + nr_stack_trace_entries;

        trace->skip = 3;

        save_stack_trace(trace);

        /*
         * Some daft arches put -1 at the end to indicate its a full trace.
         *
         * <rant> this is buggy anyway, since it takes a whole extra entry so a
         * complete trace that maxes out the entries provided will be reported
         * as incomplete, friggin useless </rant>
         */
        if (trace->nr_entries != 0 &&
            trace->entries[trace->nr_entries-1] == ULONG_MAX)
                trace->nr_entries--;

        trace->max_entries = trace->nr_entries;

        nr_stack_trace_entries += trace->nr_entries;

        if (nr_stack_trace_entries >= MAX_STACK_TRACE_ENTRIES-1) {
                if (!debug_locks_off_graph_unlock())
                        return 0;

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

                return 0;
        }

        return 1;
}

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

/*
 * 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",
};

const char * __get_key_name(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)
{
        char c = '.';

        if (class->usage_mask & lock_flag(bit + 2))
                c = '+';
        if (class->usage_mask & lock_flag(bit)) {
                c = '-';
                if (class->usage_mask & lock_flag(bit + 2))
                        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}", usage);
}

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.
         */
        unsigned int class_idx = hlock->class_idx;

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

        if (!class_idx || (class_idx - 1) >= MAX_LOCKDEP_KEYS) {
                printk(KERN_CONT "<RELEASED>\n");
                return;
        }

        printk(KERN_CONT "%p", hlock->instance);
        print_lock_name(lock_classes + class_idx - 1);
        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->state == TASK_RUNNING && p != current)
                return;
        for (i = 0; i < depth; i++) {
                printk(" #%d: ", i);
                print_lock(p->held_locks + i);
        }
}

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

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

/*
 * Is this the address of a static object:
 */
#ifdef __KERNEL__
static int static_obj(void *obj)
{
        unsigned long start = (unsigned long) &_stext,
                      end   = (unsigned long) &_end,
                      addr  = (unsigned long) obj;

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

        if (arch_is_kernel_data(addr))
                return 1;

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

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

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

        if (!new_class->name)
                return 0;

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

        return count + 1;
}

static inline 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)) {
                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();
                return NULL;
        }

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

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

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

        hash_head = classhashentry(key);

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

        hlist_for_each_entry_rcu(class, hash_head, hash_entry) {
                if (class->key == key) {
                        /*
                         * Huh! same key, different name? Did someone trample
                         * on some memory? We're most confused.
                         */
                        WARN_ON_ONCE(class->name != lock->name);
                        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;

        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.\n");
                pr_err("turning off the locking correctness validator.\n");
                dump_stack();
                return false;
        }

        return true;
}

/*
 * 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)) {
                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;
        }

        /*
         * Allocate a new key from the static array, and add it to
         * the hash:
         */
        if (nr_lock_classes >= MAX_LOCKDEP_KEYS) {
                if (!debug_locks_off_graph_unlock()) {
                        return NULL;
                }

                print_lockdep_off("BUG: MAX_LOCKDEP_KEYS too low!");
                dump_stack();
                return NULL;
        }
        class = lock_classes + nr_lock_classes++;
        debug_atomic_inc(nr_unused_locks);
        class->key = key;
        class->name = lock->name;
        class->subclass = subclass;
        INIT_LIST_HEAD(&class->locks_before);
        INIT_LIST_HEAD(&class->locks_after);
        class->name_version = count_matching_names(class);
        /*
         * 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);
        /*
         * Add it to the global list of classes:
         */
        list_add_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)
{
        if (nr_list_entries >= MAX_LOCKDEP_ENTRIES) {
                if (!debug_locks_off_graph_unlock())
                        return NULL;

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

/*
 * Add a new dependency to the head of the list:
 */
static int add_lock_to_list(struct lock_class *this, struct list_head *head,
                            unsigned long ip, int distance,
                            struct stack_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->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         4096UL
#define CQ_MASK                         (MAX_CIRCULAR_QUEUE_SIZE-1)

/*
 * The circular_queue and helpers is used to implement the
 * breadth-first search(BFS)algorithem, by which we can build
 * the shortest path from the next lock to be acquired to the
 * previous held lock if there is a circular between them.
 */
struct circular_queue {
        unsigned long 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, unsigned long elem)
{
        if (__cq_full(cq))
                return -1;

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

static inline int __cq_dequeue(struct circular_queue *cq, unsigned long *elem)
{
        if (__cq_empty(cq))
                return -1;

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

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,
                                        struct lock_list *parent)
{
        unsigned long nr;

        nr = lock - list_entries;
        WARN_ON(nr >= nr_list_entries); /* Out-of-bounds, input fail */
        lock->parent = parent;
        lock->class->dep_gen_id = lockdep_dependency_gen_id;
}

static inline unsigned long lock_accessed(struct lock_list *lock)
{
        unsigned long nr;

        nr = lock - list_entries;
        WARN_ON(nr >= nr_list_entries); /* Out-of-bounds, input fail */
        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;
}

static int __bfs(struct lock_list *source_entry,
                 void *data,
                 int (*match)(struct lock_list *entry, void *data),
                 struct lock_list **target_entry,
                 int forward)
{
        struct lock_list *entry;
        struct list_head *head;
        struct circular_queue *cq = &lock_cq;
        int ret = 1;

        if (match(source_entry, data)) {
                *target_entry = source_entry;
                ret = 0;
                goto exit;
        }

        if (forward)
                head = &source_entry->class->locks_after;
        else
                head = &source_entry->class->locks_before;

        if (list_empty(head))
                goto exit;

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

        while (!__cq_empty(cq)) {
                struct lock_list *lock;

                __cq_dequeue(cq, (unsigned long *)&lock);

                if (!lock->class) {
                        ret = -2;
                        goto exit;
                }

                if (forward)
                        head = &lock->class->locks_after;
                else
                        head = &lock->class->locks_before;

                DEBUG_LOCKS_WARN_ON(!irqs_disabled());

                list_for_each_entry_rcu(entry, head, entry) {
                        if (!lock_accessed(entry)) {
                                unsigned int cq_depth;
                                mark_lock_accessed(entry, lock);
                                if (match(entry, data)) {
                                        *target_entry = entry;
                                        ret = 0;
                                        goto exit;
                                }

                                if (__cq_enqueue(cq, (unsigned long)entry)) {
                                        ret = -1;
                                        goto exit;
                                }
                                cq_depth = __cq_get_elem_count(cq);
                                if (max_bfs_queue_depth < cq_depth)
                                        max_bfs_queue_depth = cq_depth;
                        }
                }
        }
exit:
        return ret;
}

static inline int __bfs_forwards(struct lock_list *src_entry,
                        void *data,
                        int (*match)(struct lock_list *entry, void *data),
                        struct lock_list **target_entry)
{
        return __bfs(src_entry, data, match, target_entry, 1);

}

static inline int __bfs_backwards(struct lock_list *src_entry,
                        void *data,
                        int (*match)(struct lock_list *entry, void *data),
                        struct lock_list **target_entry)
{
        return __bfs(src_entry, data, match, target_entry, 0);

}

/*
 * Recursive, forwards-direction lock-dependency checking, used for
 * both noncyclic checking and for hardirq-unsafe/softirq-unsafe
 * checking.
 */

/*
 * Print a dependency chain entry (this is only done when a deadlock
 * has been detected):
 */
static noinline int
print_circular_bug_entry(struct lock_list *target, int depth)
{
        if (debug_locks_silent)
                return 0;
        printk("\n-> #%u", depth);
        print_lock_name(target->class);
        printk(KERN_CONT ":\n");
        print_stack_trace(&target->trace, 6);

        return 0;
}

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 int
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 0;

        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);

        return 0;
}

static inline int class_equal(struct lock_list *entry, void *data)
{
        return entry->class == data;
}

static noinline int print_circular_bug(struct lock_list *this,
                                struct lock_list *target,
                                struct held_lock *check_src,
                                struct held_lock *check_tgt,
                                struct stack_trace *trace)
{
        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 0;

        if (!save_trace(&this->trace))
                return 0;

        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();

        return 0;
}

static noinline int print_bfs_bug(int ret)
{
        if (!debug_locks_off_graph_unlock())
                return 0;

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

        return 0;
}

static int noop_count(struct lock_list *entry, void *data)
{
        (*(unsigned long *)data)++;
        return 0;
}

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

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

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

        this.parent = NULL;
        this.class = class;

        raw_local_irq_save(flags);
        arch_spin_lock(&lockdep_lock);
        ret = __lockdep_count_forward_deps(&this);
        arch_spin_unlock(&lockdep_lock);
        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 *uninitialized_var(target_entry);

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

        return count;
}

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

        this.parent = NULL;
        this.class = class;

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

        return ret;
}

/*
 * Prove that the dependency graph starting at <entry> can not
 * lead to <target>. Print an error and return 0 if it does.
 */
static noinline int
check_noncircular(struct lock_list *root, struct lock_class *target,
                struct lock_list **target_entry)
{
        int result;

        debug_atomic_inc(nr_cyclic_checks);

        result = __bfs_forwards(root, target, class_equal, target_entry);

        return result;
}

static noinline int
check_redundant(struct lock_list *root, struct lock_class *target,
                struct lock_list **target_entry)
{
        int result;

        debug_atomic_inc(nr_redundant_checks);

        result = __bfs_forwards(root, target, class_equal, target_entry);

        return result;
}

#if defined(CONFIG_TRACE_IRQFLAGS) && defined(CONFIG_PROVE_LOCKING)
/*
 * 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.
 */

static inline int usage_match(struct lock_list *entry, void *bit)
{
        return entry->class->usage_mask & (1 << (enum lock_usage_bit)bit);
}



/*
 * Find a node in the forwards-direction dependency sub-graph starting
 * at @root->class that matches @bit.
 *
 * Return 0 if such a node exists in the subgraph, and put that node
 * into *@target_entry.
 *
 * Return 1 otherwise and keep *@target_entry unchanged.
 * Return <0 on error.
 */
static int
find_usage_forwards(struct lock_list *root, enum lock_usage_bit bit,
                        struct lock_list **target_entry)
{
        int result;

        debug_atomic_inc(nr_find_usage_forwards_checks);

        result = __bfs_forwards(root, (void *)bit, usage_match, target_entry);

        return result;
}

/*
 * Find a node in the backwards-direction dependency sub-graph starting
 * at @root->class that matches @bit.
 *
 * Return 0 if such a node exists in the subgraph, and put that node
 * into *@target_entry.
 *
 * Return 1 otherwise and keep *@target_entry unchanged.
 * Return <0 on error.
 */
static int
find_usage_backwards(struct lock_list *root, enum lock_usage_bit bit,
                        struct lock_list **target_entry)
{
        int result;

        debug_atomic_inc(nr_find_usage_backwards_checks);

        result = __bfs_backwards(root, (void *)bit, usage_match, 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_USAGE_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_stack_trace(class->usage_traces + bit, len);
                }
        }
        printk("%*s }\n", depth, "");

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

/*
 * printk the shortest lock dependencies from @start to @end in reverse order:
 */
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_stack_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));

        return;
}

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 int
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 0;

        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),
                curr->hardirq_context, hardirq_count() >> HARDIRQ_SHIFT,
                curr->softirq_context, softirq_count() >> SOFTIRQ_SHIFT,
                curr->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_stack_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_stack_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);
        if (!save_trace(&prev_root->trace))
                return 0;
        print_shortest_lock_dependencies(backwards_entry, prev_root);

        pr_warn("\nthe dependencies between the lock to be acquired");
        pr_warn(" and %s-irq-unsafe lock:\n", irqclass);
        if (!save_trace(&next_root->trace))
                return 0;
        print_shortest_lock_dependencies(forwards_entry, next_root);

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

        return 0;
}

static int
check_usage(struct task_struct *curr, struct held_lock *prev,
            struct held_lock *next, enum lock_usage_bit bit_backwards,
            enum lock_usage_bit bit_forwards, const char *irqclass)
{
        int ret;
        struct lock_list this, that;
        struct lock_list *uninitialized_var(target_entry);
        struct lock_list *uninitialized_var(target_entry1);

        this.parent = NULL;

        this.class = hlock_class(prev);
        ret = find_usage_backwards(&this, bit_backwards, &target_entry);
        if (ret < 0)
                return print_bfs_bug(ret);
        if (ret == 1)
                return ret;

        that.parent = NULL;
        that.class = hlock_class(next);
        ret = find_usage_forwards(&that, bit_forwards, &target_entry1);
        if (ret < 0)
                return print_bfs_bug(ret);
        if (ret == 1)
                return ret;

        return print_bad_irq_dependency(curr, &this, &that,
                        target_entry, target_entry1,
                        prev, next,
                        bit_backwards, bit_forwards, irqclass);
}

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)
{
        return (bit & 1) ? state_rnames[bit >> 2] : state_names[bit >> 2];
}

static int exclusive_bit(int new_bit)
{
        /*
         * USED_IN
         * USED_IN_READ
         * ENABLED
         * ENABLED_READ
         *
         * bit 0 - write/read
         * bit 1 - used_in/enabled
         * bit 2+  state
         */

        int state = new_bit & ~3;
        int dir = new_bit & 2;

        /*
         * keep state, bit flip the direction and strip read.
         */
        return state | (dir ^ 2);
}

static int check_irq_usage(struct task_struct *curr, struct held_lock *prev,
                           struct held_lock *next, enum lock_usage_bit bit)
{
        /*
         * Prove that the new dependency does not connect a hardirq-safe
         * lock with a hardirq-unsafe lock - to achieve this we search
         * the backwards-subgraph starting at <prev>, and the
         * forwards-subgraph starting at <next>:
         */
        if (!check_usage(curr, prev, next, bit,
                           exclusive_bit(bit), state_name(bit)))
                return 0;

        bit++; /* _READ */

        /*
         * 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>:
         */
        if (!check_usage(curr, prev, next, bit,
                           exclusive_bit(bit), state_name(bit)))
                return 0;

        return 1;
}

static int
check_prev_add_irq(struct task_struct *curr, struct held_lock *prev,
                struct held_lock *next)
{
#define LOCKDEP_STATE(__STATE)                                          \
        if (!check_irq_usage(curr, prev, next, LOCK_USED_IN_##__STATE)) \
                return 0;
#include "lockdep_states.h"
#undef LOCKDEP_STATE

        return 1;
}

static void inc_chains(void)
{
        if (current->hardirq_context)
                nr_hardirq_chains++;
        else {
                if (current->softirq_context)
                        nr_softirq_chains++;
                else
                        nr_process_chains++;
        }
}

#else

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

static inline void inc_chains(void)
{
        nr_process_chains++;
}

#endif

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 int
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 0;

        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();

        return 0;
}

/*
 * 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 on recursive read
 */
static int
check_deadlock(struct task_struct *curr, struct held_lock *next,
               struct lockdep_map *next_instance, int read)
{
        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 ((read == 2) && prev->read)
                        return 2;

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

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

/*
 * There was a chain-cache miss, and we are about to add a new dependency
 * to a previous lock. We recursively 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, int distance, struct stack_trace *trace,
               int (*save)(struct stack_trace *trace))
{
        struct lock_list *uninitialized_var(target_entry);
        struct lock_list *entry;
        struct lock_list this;
        int ret;

        /*
         * Prove that the new <prev> -> <next> dependency would not
         * create a circular dependency in the graph. (We do this by
         * forward-recursing into the graph starting at <next>, and
         * checking whether we can reach <prev>.)
         *
         * We are using global variables to control the recursion, to
         * keep the stackframe size of the recursive functions low:
         */
        this.class = hlock_class(next);
        this.parent = NULL;
        ret = check_noncircular(&this, hlock_class(prev), &target_entry);
        if (unlikely(!ret)) {
                if (!trace->entries) {
                        /*
                         * If @save fails here, the printing might trigger
                         * a WARN but because of the !nr_entries it should
                         * not do bad things.
                         */
                        save(trace);
                }
                return print_circular_bug(&this, target_entry, next, prev, trace);
        }
        else if (unlikely(ret < 0))
                return print_bfs_bug(ret);

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

        /*
         * For recursive read-locks we do all the dependency checks,
         * but we dont store read-triggered dependencies (only
         * write-triggered dependencies). This ensures that only the
         * write-side dependencies matter, and that if for example a
         * write-lock never takes any other locks, then the reads are
         * equivalent to a NOP.
         */
        if (next->read == 2 || prev->read == 2)
                return 1;
        /*
         * 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;
                        return 1;
                }
        }

        /*
         * Is the <prev> -> <next> link redundant?
         */
        this.class = hlock_class(prev);
        this.parent = NULL;
        ret = check_redundant(&this, hlock_class(next), &target_entry);
        if (!ret) {
                debug_atomic_inc(nr_redundant);
                return 2;
        }
        if (ret < 0)
                return print_bfs_bug(ret);


        if (!trace->entries && !save(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)->locks_after,
                               next->acquire_ip, distance, trace);

        if (!ret)
                return 0;

        ret = add_lock_to_list(hlock_class(prev),
                               &hlock_class(next)->locks_before,
                               next->acquire_ip, distance, 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)
{
        int depth = curr->lockdep_depth;
        struct held_lock *hlock;
        struct stack_trace trace = {
                .nr_entries = 0,
                .max_entries = 0,
                .entries = NULL,
                .skip = 0,
        };

        /*
         * 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 (;;) {
                int distance = curr->lockdep_depth - depth + 1;
                hlock = curr->held_locks + depth - 1;

                /*
                 * Only non-recursive-read entries get new dependencies
                 * added:
                 */
                if (hlock->read != 2 && hlock->check) {
                        int ret = check_prev_add(curr, hlock, next, distance, &trace, save_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;
}

unsigned long nr_lock_chains;
struct lock_chain lock_chains[MAX_LOCKDEP_CHAINS];
int nr_chain_hlocks;
static u16 chain_hlocks[MAX_LOCKDEP_CHAIN_HLOCKS];

struct lock_class *lock_chain_get_class(struct lock_chain *chain, int i)
{
        return lock_classes + chain_hlocks[chain->base + i];
}

/*
 * 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(int class_idx, u64 chain_key)
{
        u64 new_chain_key = iterate_chain_key(chain_key, class_idx);

        printk(" class_idx:%d -> chain_key:%016Lx",
                class_idx,
                (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 = 0;
        int depth = curr->lockdep_depth;
        int i;

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

                print_lock(hlock);
        }

        print_chain_key_iteration(hlock_next->class_idx, chain_key);
        print_lock(hlock_next);
}

static void print_chain_keys_chain(struct lock_chain *chain)
{
        int i;
        u64 chain_key = 0;
        int class_id;

        printk("depth: %u\n", chain->depth);
        for (i = 0; i < chain->depth; i++) {
                class_id = chain_hlocks[chain->base + i];
                chain_key = print_chain_key_iteration(class_id + 1, chain_key);

                print_lock_name(lock_classes + class_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 = curr->held_locks[i].class_idx - 1;

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

/*
 * 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 lock_class *class = hlock_class(hlock);
        struct hlist_head *hash_head = chainhashentry(chain_key);
        struct lock_chain *chain;
        int i, j;

        /*
         * Allocate a new chain entry from the static array, and add
         * it to the hash:
         */

        /*
         * We might need to take 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 (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
                return 0;

        if (unlikely(nr_lock_chains >= MAX_LOCKDEP_CHAINS)) {
                if (!debug_locks_off_graph_unlock())
                        return 0;

                print_lockdep_off("BUG: MAX_LOCKDEP_CHAINS too low!");
                dump_stack();
                return 0;
        }
        chain = lock_chains + nr_lock_chains++;
        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));

        if (likely(nr_chain_hlocks + chain->depth <= MAX_LOCKDEP_CHAIN_HLOCKS)) {
                chain->base = nr_chain_hlocks;
                for (j = 0; j < chain->depth - 1; j++, i++) {
                        int lock_id = curr->held_locks[i].class_idx - 1;
                        chain_hlocks[chain->base + j] = lock_id;
                }
                chain_hlocks[chain->base + j] = class - lock_classes;
        }

        if (nr_chain_hlocks < MAX_LOCKDEP_CHAIN_HLOCKS)
                nr_chain_hlocks += chain->depth;

#ifdef CONFIG_DEBUG_LOCKDEP
        /*
         * Important for check_no_collision().
         */
        if (unlikely(nr_chain_hlocks > MAX_LOCKDEP_CHAIN_HLOCKS)) {
                if (!debug_locks_off_graph_unlock())
                        return 0;

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

        hlist_add_head_rcu(&chain->entry, hash_head);
        debug_atomic_inc(chain_lookup_misses);
        inc_chains();

        return 1;
}

/*
 * Look up a dependency chain.
 */
static inline struct lock_chain *lookup_chain_cache(u64 chain_key)
{
        struct hlist_head *hash_head = chainhashentry(chain_key);
        struct lock_chain *chain;

        /*
         * We can walk it lock-free, because entries only get added
         * to the hash:
         */
        hlist_for_each_entry_rcu(chain, hash_head, entry) {
                if (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 lockdep_map *lock,
                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.
                 *
                 * any of these scenarios could lead to a deadlock. If
                 * All validations
                 */
                int ret = check_deadlock(curr, hlock, lock, hlock->read);

                if (!ret)
                        return 0;
                /*
                 * Mark recursive read, as we jump over it when
                 * building dependencies (just like we jump over
                 * trylock entries):
                 */
                if (ret == 2)
                        hlock->read = 2;
                /*
                 * Add dependency only if this lock is not the head
                 * of the chain, and if it's not a secondary read-lock:
                 */
                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 lockdep_map *lock, struct held_lock *hlock,
                int chain_head, u64 chain_key)
{
        return 1;
}
#endif

/*
 * 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 = 0;

        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;
                }
                /*
                 * Whoops ran out of static storage again?
                 */
                if (DEBUG_LOCKS_WARN_ON(hlock->class_idx > MAX_LOCKDEP_KEYS))
                        return;

                if (prev_hlock && (prev_hlock->irq_context !=
                                                        hlock->irq_context))
                        chain_key = 0;
                chain_key = iterate_chain_key(chain_key, hlock->class_idx);
                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
}

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 int
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_graph_unlock() || debug_locks_silent)
                return 0;

        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),
                trace_hardirq_context(curr), hardirq_count() >> HARDIRQ_SHIFT,
                trace_softirq_context(curr), softirq_count() >> SOFTIRQ_SHIFT,
                trace_hardirqs_enabled(curr),
                trace_softirqs_enabled(curr));
        print_lock(this);

        pr_warn("{%s} state was registered at:\n", usage_str[prev_bit]);
        print_stack_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();

        return 0;
}

/*
 * 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)))
                return print_usage_bug(curr, this, bad_bit, new_bit);
        return 1;
}

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

#if defined(CONFIG_TRACE_IRQFLAGS) && defined(CONFIG_PROVE_LOCKING)

/*
 * print irq inversion bug:
 */
static int
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 0;

        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,
                        middle ? middle->class : other->class, root->class);

        lockdep_print_held_locks(curr);

        pr_warn("\nthe shortest dependencies between 2nd lock and 1st lock:\n");
        if (!save_trace(&root->trace))
                return 0;
        print_shortest_lock_dependencies(other, root);

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

        return 0;
}

/*
 * Prove that in the forwards-direction subgraph starting at <this>
 * there is no lock matching <mask>:
 */
static int
check_usage_forwards(struct task_struct *curr, struct held_lock *this,
                     enum lock_usage_bit bit, const char *irqclass)
{
        int ret;
        struct lock_list root;
        struct lock_list *uninitialized_var(target_entry);

        root.parent = NULL;
        root.class = hlock_class(this);
        ret = find_usage_forwards(&root, bit, &target_entry);
        if (ret < 0)
                return print_bfs_bug(ret);
        if (ret == 1)
                return ret;

        return print_irq_inversion_bug(curr, &root, target_entry,
                                        this, 1, irqclass);
}

/*
 * Prove that in the backwards-direction subgraph starting at <this>
 * there is no lock matching <mask>:
 */
static int
check_usage_backwards(struct task_struct *curr, struct held_lock *this,
                      enum lock_usage_bit bit, const char *irqclass)
{
        int ret;
        struct lock_list root;
        struct lock_list *uninitialized_var(target_entry);

        root.parent = NULL;
        root.class = hlock_class(this);
        ret = find_usage_backwards(&root, bit, &target_entry);
        if (ret < 0)
                return print_bfs_bug(ret);
        if (ret == 1)
                return ret;

        return print_irq_inversion_bug(curr, &root, target_entry,
                                        this, 0, irqclass);
}

void print_irqtrace_events(struct task_struct *curr)
{
        printk("irq event stamp: %u\n", curr->irq_events);
        printk("hardirqs last  enabled at (%u): [<%px>] %pS\n",
                curr->hardirq_enable_event, (void *)curr->hardirq_enable_ip,
                (void *)curr->hardirq_enable_ip);
        printk("hardirqs last disabled at (%u): [<%px>] %pS\n",
                curr->hardirq_disable_event, (void *)curr->hardirq_disable_ip,
                (void *)curr->hardirq_disable_ip);
        printk("softirqs last  enabled at (%u): [<%px>] %pS\n",
                curr->softirq_enable_event, (void *)curr->softirq_enable_ip,
                (void *)curr->softirq_enable_ip);
        printk("softirqs last disabled at (%u): [<%px>] %pS\n",
                curr->softirq_disable_event, (void *)curr->softirq_disable_ip,
                (void *)curr->softirq_disable_ip);
}

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

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

#define STRICT_READ_CHECKS      1

static int (*state_verbose_f[])(struct lock_class *class) = {
#define LOCKDEP_STATE(__STATE) \
        __STATE##_verbose,
#include "lockdep_states.h"
#undef LOCKDEP_STATE
};

static inline int state_verbose(enum lock_usage_bit bit,
                                struct lock_class *class)
{
        return state_verbose_f[bit >> 2](class);
}

typedef int (*check_usage_f)(struct task_struct *, struct held_lock *,
                             enum lock_usage_bit bit, const char *name);

static int
mark_lock_irq(struct task_struct *curr, struct held_lock *this,
                enum lock_usage_bit new_bit)
{
        int excl_bit = exclusive_bit(new_bit);
        int read = new_bit & 1;
        int dir = new_bit & 2;

        /*
         * mark USED_IN has to look forwards -- to ensure no dependency
         * has ENABLED state, which would allow recursion deadlocks.
         *
         * mark ENABLED has to look backwards -- to ensure no dependee
         * has USED_IN state, which, again, would allow  recursion deadlocks.
         */
        check_usage_f usage = dir ?
                check_usage_backwards : check_usage_forwards;

        /*
         * Validate that this particular lock does not have conflicting
         * usage states.
         */
        if (!valid_state(curr, this, new_bit, excl_bit))
                return 0;

        /*
         * Validate that the lock dependencies don't have conflicting usage
         * states.
         */
        if ((!read || !dir || STRICT_READ_CHECKS) &&
                        !usage(curr, this, excl_bit, state_name(new_bit & ~1)))
                return 0;

        /*
         * Check for read in write conflicts
         */
        if (!read) {
                if (!valid_state(curr, this, new_bit, excl_bit + 1))
                        return 0;

                if (STRICT_READ_CHECKS &&
                        !usage(curr, this, excl_bit + 1,
                                state_name(new_bit + 1)))
                        return 0;
        }

        if (state_verbose(new_bit, hlock_class(this)))
                return 2;

        return 1;
}

enum mark_type {
#define LOCKDEP_STATE(__STATE)  __STATE,
#include "lockdep_states.h"
#undef LOCKDEP_STATE
};

/*
 * Mark all held locks with a usage bit:
 */
static int
mark_held_locks(struct task_struct *curr, enum mark_type mark)
{
        enum lock_usage_bit usage_bit;
        struct held_lock *hlock;
        int i;

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

                usage_bit = 2 + (mark << 2); /* ENABLED */
                if (hlock->read)
                        usage_bit += 1; /* READ */

                BUG_ON(usage_bit >= LOCK_USAGE_STATES);

                if (!hlock->check)
                        continue;

                if (!mark_lock(curr, hlock, usage_bit))
                        return 0;
        }

        return 1;
}

/*
 * Hardirqs will be enabled:
 */
static void __trace_hardirqs_on_caller(unsigned long ip)
{
        struct task_struct *curr = current;

        /* we'll do an OFF -> ON transition: */
        curr->hardirqs_enabled = 1;

        /*
         * We are going to turn hardirqs on, so set the
         * usage bit for all held locks:
         */
        if (!mark_held_locks(curr, HARDIRQ))
                return;
        /*
         * If we have softirqs enabled, then set the usage
         * bit for all held locks. (disabled hardirqs prevented
         * this bit from being set before)
         */
        if (curr->softirqs_enabled)
                if (!mark_held_locks(curr, SOFTIRQ))
                        return;

        curr->hardirq_enable_ip = ip;
        curr->hardirq_enable_event = ++curr->irq_events;
        debug_atomic_inc(hardirqs_on_events);
}

void lockdep_hardirqs_on(unsigned long ip)
{
        if (unlikely(!debug_locks || current->lockdep_recursion))
                return;

        if (unlikely(current->hardirqs_enabled)) {
                /*
                 * Neither irq nor preemption are disabled here
                 * so this is racy by nature but losing one hit
                 * in a stat is not a big deal.
                 */
                __debug_atomic_inc(redundant_hardirqs_on);
                return;
        }

        /*
         * We're enabling irqs and according to our state above irqs weren't
         * already enabled, yet we find the hardware thinks they are in fact
         * enabled.. someone messed up their IRQ state tracing.
         */
        if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
                return;

        /*
         * See the fine text that goes along with this variable definition.
         */
        if (DEBUG_LOCKS_WARN_ON(unlikely(early_boot_irqs_disabled)))
                return;

        /*
         * Can't allow enabling interrupts while in an interrupt handler,
         * that's general bad form and such. Recursion, limited stack etc..
         */
        if (DEBUG_LOCKS_WARN_ON(current->hardirq_context))
                return;

        current->lockdep_recursion = 1;
        __trace_hardirqs_on_caller(ip);
        current->lockdep_recursion = 0;
}
NOKPROBE_SYMBOL(lockdep_hardirqs_on);

/*
 * Hardirqs were disabled:
 */
void lockdep_hardirqs_off(unsigned long ip)
{
        struct task_struct *curr = current;

        if (unlikely(!debug_locks || current->lockdep_recursion))
                return;

        /*
         * So we're supposed to get called after you mask local IRQs, but for
         * some reason the hardware doesn't quite think you did a proper job.
         */
        if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
                return;

        if (curr->hardirqs_enabled) {
                /*
                 * We have done an ON -> OFF transition:
                 */
                curr->hardirqs_enabled = 0;
                curr->hardirq_disable_ip = ip;
                curr->hardirq_disable_event = ++curr->irq_events;
                debug_atomic_inc(hardirqs_off_events);
        } else
                debug_atomic_inc(redundant_hardirqs_off);
}
NOKPROBE_SYMBOL(lockdep_hardirqs_off);

/*
 * Softirqs will be enabled:
 */
void trace_softirqs_on(unsigned long ip)
{
        struct task_struct *curr = current;

        if (unlikely(!debug_locks || current->lockdep_recursion))
                return;

        /*
         * We fancy IRQs being disabled here, see softirq.c, avoids
         * funny state and nesting things.
         */
        if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
                return;

        if (curr->softirqs_enabled) {
                debug_atomic_inc(redundant_softirqs_on);
                return;
        }

        current->lockdep_recursion = 1;
        /*
         * We'll do an OFF -> ON transition:
         */
        curr->softirqs_enabled = 1;
        curr->softirq_enable_ip = ip;
        curr->softirq_enable_event = ++curr->irq_events;
        debug_atomic_inc(softirqs_on_events);
        /*
         * We are going to turn softirqs on, so set the
         * usage bit for all held locks, if hardirqs are
         * enabled too:
         */
        if (curr->hardirqs_enabled)
                mark_held_locks(curr, SOFTIRQ);
        current->lockdep_recursion = 0;
}

/*
 * Softirqs were disabled:
 */
void trace_softirqs_off(unsigned long ip)
{
        struct task_struct *curr = current;

        if (unlikely(!debug_locks || current->lockdep_recursion))
                return;

        /*
         * We fancy IRQs being disabled here, see softirq.c
         */
        if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
                return;

        if (curr->softirqs_enabled) {
                /*
                 * We have done an ON -> OFF transition:
                 */
                curr->softirqs_enabled = 0;
                curr->softirq_disable_ip = ip;
                curr->softirq_disable_event = ++curr->irq_events;
                debug_atomic_inc(softirqs_off_events);
                /*
                 * Whoops, we wanted softirqs off, so why aren't they?
                 */
                DEBUG_LOCKS_WARN_ON(!softirq_count());
        } else
                debug_atomic_inc(redundant_softirqs_off);
}

static int mark_irqflags(struct task_struct *curr, struct held_lock *hlock)
{
        /*
         * If non-trylock use in a hardirq or softirq context, then
         * mark the lock as used in these contexts:
         */
        if (!hlock->trylock) {
                if (hlock->read) {
                        if (curr->hardirq_context)
                                if (!mark_lock(curr, hlock,
                                                LOCK_USED_IN_HARDIRQ_READ))
                                        return 0;
                        if (curr->softirq_context)
                                if (!mark_lock(curr, hlock,
                                                LOCK_USED_IN_SOFTIRQ_READ))
                                        return 0;
                } else {
                        if (curr->hardirq_context)
                                if (!mark_lock(curr, hlock, LOCK_USED_IN_HARDIRQ))
                                        return 0;
                        if (curr->softirq_context)
                                if (!mark_lock(curr, hlock, LOCK_USED_IN_SOFTIRQ))
                                        return 0;
                }
        }
        if (!hlock->hardirqs_off) {
                if (hlock->read) {
                        if (!mark_lock(curr, hlock,
                                        LOCK_ENABLED_HARDIRQ_READ))
                                return 0;
                        if (curr->softirqs_enabled)
                                if (!mark_lock(curr, hlock,
                                                LOCK_ENABLED_SOFTIRQ_READ))
                                        return 0;
                } else {
                        if (!mark_lock(curr, hlock,
                                        LOCK_ENABLED_HARDIRQ))
                                return 0;
                        if (curr->softirqs_enabled)
                                if (!mark_lock(curr, hlock,
                                                LOCK_ENABLED_SOFTIRQ))
                                        return 0;
                }
        }

        return 1;
}

static inline unsigned int task_irq_context(struct task_struct *task)
{
        return 2 * !!task->hardirq_context + !!task->softirq_context;
}

static int separate_irq_context(struct task_struct *curr,
                struct held_lock *hlock)
{
        unsigned int depth = curr->lockdep_depth;

        /*
         * Keep track of points where we cross into an interrupt context:
         */
        if (depth) {
                struct held_lock *prev_hlock;

                prev_hlock = curr->held_locks + depth-1;
                /*
                 * If we cross into another context, reset the
                 * hash key (this also prevents the checking and the
                 * adding of the dependency to 'prev'):
                 */
                if (prev_hlock->irq_context != hlock->irq_context)
                        return 1;
        }
        return 0;
}

#else /* defined(CONFIG_TRACE_IRQFLAGS) && defined(CONFIG_PROVE_LOCKING) */

static inline
int mark_lock_irq(struct task_struct *curr, struct held_lock *this,
                enum lock_usage_bit new_bit)
{
        WARN_ON(1); /* Impossible innit? when we don't have TRACE_IRQFLAG */
        return 1;
}

static inline int mark_irqflags(struct task_struct *curr,
                struct held_lock *hlock)
{
        return 1;
}

static inline unsigned int task_irq_context(struct task_struct *task)
{
        return 0;
}

static inline int separate_irq_context(struct task_struct *curr,
                struct held_lock *hlock)
{
        return 0;
}

#endif /* defined(CONFIG_TRACE_IRQFLAGS) && defined(CONFIG_PROVE_LOCKING) */

/*
 * Mark a lock with a usage bit, and validate the state transition:
 */
static int mark_lock(struct task_struct *curr, struct held_lock *this,
                             enum lock_usage_bit new_bit)
{
        unsigned int new_mask = 1 << new_bit, ret = 1;

        /*
         * If already set then do not dirty the cacheline,
         * nor do any checks:
         */
        if (likely(hlock_class(this)->usage_mask & new_mask))
                return 1;

        if (!graph_lock())
                return 0;
        /*
         * Make sure we didn't race:
         */
        if (unlikely(hlock_class(this)->usage_mask & new_mask)) {
                graph_unlock();
                return 1;
        }

        hlock_class(this)->usage_mask |= new_mask;

        if (!save_trace(hlock_class(this)->usage_traces + new_bit))
                return 0;

        switch (new_bit) {
#define LOCKDEP_STATE(__STATE)                  \
        case LOCK_USED_IN_##__STATE:            \
        case LOCK_USED_IN_##__STATE##_READ:     \
        case LOCK_ENABLED_##__STATE:            \
        case LOCK_ENABLED_##__STATE##_READ:
#include "lockdep_states.h"
#undef LOCKDEP_STATE
                ret = mark_lock_irq(curr, this, new_bit);
                if (!ret)
                        return 0;
                break;
        case LOCK_USED:
                debug_atomic_dec(nr_unused_locks);
                break;
        default:
                if (!debug_locks_off_graph_unlock())
                        return 0;
                WARN_ON(1);
                return 0;
        }

        graph_unlock();

        /*
         * We must printk outside of the graph_lock:
         */
        if (ret == 2) {
                printk("\nmarked lock as {%s}:\n", usage_str[new_bit]);
                print_lock(this);
                print_irqtrace_events(curr);
                dump_stack();
        }

        return ret;
}

/*
 * Initialize a lock instance's lock-class mapping info:
 */
void lockdep_init_map(struct lockdep_map *lock, const char *name,
                      struct lock_class_key *key, int subclass)
{
        int i;

        for (i = 0; i < NR_LOCKDEP_CACHING_CLASSES; i++)
                lock->class_cache[i] = NULL;

#ifdef CONFIG_LOCK_STAT
        lock->cpu = raw_smp_processor_id();
#endif

        /*
         * Can't be having no nameless bastards around this place!
         */
        if (DEBUG_LOCKS_WARN_ON(!name)) {
                lock->name = "NULL";
                return;
        }

        lock->name = name;

        /*
         * No key, no joy, we need to hash something.
         */
        if (DEBUG_LOCKS_WARN_ON(!key))
                return;
        /*
         * Sanity check, the lock-class key must be persistent:
         */
        if (!static_obj(key)) {
                printk("BUG: key %px not in .data!\n", key);
                /*
                 * What it says above ^^^^^, I suggest you read it.
                 */
                DEBUG_LOCKS_WARN_ON(1);
                return;
        }
        lock->key = key;

        if (unlikely(!debug_locks))
                return;

        if (subclass) {
                unsigned long flags;

                if (DEBUG_LOCKS_WARN_ON(current->lockdep_recursion))
                        return;

                raw_local_irq_save(flags);
                current->lockdep_recursion = 1;
                register_lock_class(lock, subclass, 1);
                current->lockdep_recursion = 0;
                raw_local_irq_restore(flags);
        }
}
EXPORT_SYMBOL_GPL(lockdep_init_map);

struct lock_class_key __lockdep_no_validate__;
EXPORT_SYMBOL_GPL(__lockdep_no_validate__);

static int
print_lock_nested_lock_not_held(struct task_struct *curr,
                                struct held_lock *hlock,
                                unsigned long ip)
{
        if (!debug_locks_off())
                return 0;
        if (debug_locks_silent)
                return 0;

        pr_warn("\n");
        pr_warn("==================================\n");
        pr_warn("WARNING: Nested lock was not taken\n");
        print_kernel_ident();
        pr_warn("----------------------------------\n");

        pr_warn("%s/%d is trying to lock:\n", curr->comm, task_pid_nr(curr));
        print_lock(hlock);

        pr_warn("\nbut this task is not holding:\n");
        pr_warn("%s\n", hlock->nest_lock->name);

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

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

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

        return 0;
}

static int __lock_is_held(const struct lockdep_map *lock, int read);

/*
 * This gets called for every mutex_lock*()/spin_lock*() operation.
 * We maintain the dependency maps and validate the locking attempt:
 *
 * The callers must make sure that IRQs are disabled before calling it,
 * otherwise we could get an interrupt which would want to take locks,
 * which would end up in lockdep again.
 */
static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
                          int trylock, int read, int check, int hardirqs_off,
                          struct lockdep_map *nest_lock, unsigned long ip,
                          int references, int pin_count)
{
        struct task_struct *curr = current;
        struct lock_class *class = NULL;
        struct held_lock *hlock;
        unsigned int depth;
        int chain_head = 0;
        int class_idx;
        u64 chain_key;

        if (unlikely(!debug_locks))
                return 0;

        if (!prove_locking || lock->key == &__lockdep_no_validate__)
                check = 0;

        if (subclass < NR_LOCKDEP_CACHING_CLASSES)
                class = lock->class_cache[subclass];
        /*
         * Not cached?
         */
        if (unlikely(!class)) {
                class = register_lock_class(lock, subclass, 0);
                if (!class)
                        return 0;
        }

        debug_class_ops_inc(class);

        if (very_verbose(class)) {
                printk("\nacquire 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();
        }

        /*
         * Add the lock to the list of currently held locks.
         * (we dont increase the depth just yet, up until the
         * dependency checks are done)
         */
        depth = curr->lockdep_depth;
        /*
         * Ran out of static storage for our per-task lock stack again have we?
         */
        if (DEBUG_LOCKS_WARN_ON(depth >= MAX_LOCK_DEPTH))
                return 0;

        class_idx = class - lock_classes + 1;

        if (depth) {
                hlock = curr->held_locks + depth - 1;
                if (hlock->class_idx == class_idx && nest_lock) {
                        if (hlock->references) {
                                /*
                                 * Check: unsigned int references:12, overflow.
                                 */
                                if (DEBUG_LOCKS_WARN_ON(hlock->references == (1 << 12)-1))
                                        return 0;

                                hlock->references++;
                        } else {
                                hlock->references = 2;
                        }

                        return 1;
                }
        }

        hlock = curr->held_locks + depth;
        /*
         * Plain impossible, we just registered it and checked it weren't no
         * NULL like.. I bet this mushroom I ate was good!
         */
        if (DEBUG_LOCKS_WARN_ON(!class))
                return 0;
        hlock->class_idx = class_idx;
        hlock->acquire_ip = ip;
        hlock->instance = lock;
        hlock->nest_lock = nest_lock;
        hlock->irq_context = task_irq_context(curr);
        hlock->trylock = trylock;
        hlock->read = read;
        hlock->check = check;
        hlock->hardirqs_off = !!hardirqs_off;
        hlock->references = references;
#ifdef CONFIG_LOCK_STAT
        hlock->waittime_stamp = 0;
        hlock->holdtime_stamp = lockstat_clock();
#endif
        hlock->pin_count = pin_count;

        if (check && !mark_irqflags(curr, hlock))
                return 0;

        /* mark it as used: */
        if (!mark_lock(curr, hlock, LOCK_USED))
                return 0;

        /*
         * Calculate the chain hash: it's the combined hash of all the
         * lock keys along the dependency chain. We save the hash value
         * at every step so that we can get the current hash easily
         * after unlock. The chain hash is then used to cache dependency
         * results.
         *
         * The 'key ID' is what is the most compact key value to drive
         * the hash, not class->key.
         */
        /*
         * Whoops, we did it again.. ran straight out of our static allocation.
         */
        if (DEBUG_LOCKS_WARN_ON(class_idx > MAX_LOCKDEP_KEYS))
                return 0;

        chain_key = curr->curr_chain_key;
        if (!depth) {
                /*
                 * How can we have a chain hash when we ain't got no keys?!
                 */
                if (DEBUG_LOCKS_WARN_ON(chain_key != 0))
                        return 0;
                chain_head = 1;
        }

        hlock->prev_chain_key = chain_key;
        if (separate_irq_context(curr, hlock)) {
                chain_key = 0;
                chain_head = 1;
        }
        chain_key = iterate_chain_key(chain_key, class_idx);

        if (nest_lock && !__lock_is_held(nest_lock, -1))
                return print_lock_nested_lock_not_held(curr, hlock, ip);

        if (!validate_chain(curr, lock, hlock, chain_head, chain_key))
                return 0;

        curr->curr_chain_key = chain_key;
        curr->lockdep_depth++;
        check_chain_key(curr);
#ifdef CONFIG_DEBUG_LOCKDEP
        if (unlikely(!debug_locks))
                return 0;
#endif
        if (unlikely(curr->lockdep_depth >= MAX_LOCK_DEPTH)) {
                debug_locks_off();
                print_lockdep_off("BUG: MAX_LOCK_DEPTH too low!");
                printk(KERN_DEBUG "depth: %i  max: %lu!\n",
                       curr->lockdep_depth, MAX_LOCK_DEPTH);

                lockdep_print_held_locks(current);
                debug_show_all_locks();
                dump_stack();

                return 0;
        }

        if (unlikely(curr->lockdep_depth > max_lockdep_depth))
                max_lockdep_depth = curr->lockdep_depth;

        return 1;
}

static int
print_unlock_imbalance_bug(struct task_struct *curr, struct lockdep_map *lock,
                           unsigned long ip)
{
        if (!debug_locks_off())
                return 0;
        if (debug_locks_silent)
                return 0;

        pr_warn("\n");
        pr_warn("=====================================\n");
        pr_warn("WARNING: bad unlock balance detected!\n");
        print_kernel_ident();
        pr_warn("-------------------------------------\n");
        pr_warn("%s/%d is trying to release lock (",
                curr->comm, task_pid_nr(curr));
        print_lockdep_cache(lock);
        pr_cont(") at:\n");
        print_ip_sym(ip);
        pr_warn("but there are no more locks to release!\n");
        pr_warn("\nother info that might help us debug this:\n");
        lockdep_print_held_locks(curr);

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

        return 0;
}

static int match_held_lock(const struct held_lock *hlock,
                                        const struct lockdep_map *lock)
{
        if (hlock->instance == lock)
                return 1;

        if (hlock->references) {
                const struct lock_class *class = lock->class_cache[0];

                if (!class)
                        class = look_up_lock_class(lock, 0);

                /*
                 * If look_up_lock_class() failed to find a class, we're trying
                 * to test if we hold a lock that has never yet been acquired.
                 * Clearly if the lock hasn't been acquired _ever_, we're not
                 * holding it either, so report failure.
                 */
                if (!class)
                        return 0;

                /*
                 * References, but not a lock we're actually ref-counting?
                 * State got messed up, follow the sites that change ->references
                 * and try to make sense of it.
                 */
                if (DEBUG_LOCKS_WARN_ON(!hlock->nest_lock))
                        return 0;

                if (hlock->class_idx == class - lock_classes + 1)
                        return 1;
        }

        return 0;
}

/* @depth must not be zero */
static struct held_lock *find_held_lock(struct task_struct *curr,
                                        struct lockdep_map *lock,
                                        unsigned int depth, int *idx)
{
        struct held_lock *ret, *hlock, *prev_hlock;
        int i;

        i = depth - 1;
        hlock = curr->held_locks + i;
        ret = hlock;
        if (match_held_lock(hlock, lock))
                goto out;

        ret = NULL;
        for (i--, prev_hlock = hlock--;
             i >= 0;
             i--, prev_hlock = hlock--) {
                /*
                 * We must not cross into another context:
                 */
                if (prev_hlock->irq_context != hlock->irq_context) {
                        ret = NULL;
                        break;
                }
                if (match_held_lock(hlock, lock)) {
                        ret = hlock;
                        break;
                }
        }

out:
        *idx = i;
        return ret;
}

static int reacquire_held_locks(struct task_struct *curr, unsigned int depth,
                              int idx)
{
        struct held_lock *hlock;

        if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
                return 0;

        for (hlock = curr->held_locks + idx; idx < depth; idx++, hlock++) {
                if (!__lock_acquire(hlock->instance,
                                    hlock_class(hlock)->subclass,
                                    hlock->trylock,
                                    hlock->read, hlock->check,
                                    hlock->hardirqs_off,
                                    hlock->nest_lock, hlock->acquire_ip,
                                    hlock->references, hlock->pin_count))
                        return 1;
        }
        return 0;
}

static int
__lock_set_class(struct lockdep_map *lock, const char *name,
                 struct lock_class_key *key, unsigned int subclass,
                 unsigned long ip)
{
        struct task_struct *curr = current;
        struct held_lock *hlock;
        struct lock_class *class;
        unsigned int depth;
        int i;

        depth = curr->lockdep_depth;
        /*
         * This function is about (re)setting the class of a held lock,
         * yet we're not actually holding any locks. Naughty user!
         */
        if (DEBUG_LOCKS_WARN_ON(!depth))
                return 0;

        hlock = find_held_lock(curr, lock, depth, &i);
        if (!hlock)
                return print_unlock_imbalance_bug(curr, lock, ip);

        lockdep_init_map(lock, name, key, 0);
        class = register_lock_class(lock, subclass, 0);
        hlock->class_idx = class - lock_classes + 1;

        curr->lockdep_depth = i;
        curr->curr_chain_key = hlock-&