function-graph: always initialize task ret_stack

[linux-2.6] / kernel / 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 <pzijlstr@redhat.com>
 *
 * 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/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 <trace/lockdep.h>

#include <asm/sections.h>

#include "lockdep_internals.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 raw_spinlock_t lockdep_lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;

static int graph_lock(void)
{
        __raw_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) {
                __raw_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 && !__raw_spin_is_locked(&lockdep_lock))
                return DEBUG_LOCKS_WARN_ON(1);

        current->lockdep_recursion--;
        __raw_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();

        __raw_spin_unlock(&lockdep_lock);

        return ret;
}

static int lockdep_initialized;

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;
static struct lock_class lock_classes[MAX_LOCKDEP_KEYS];

static inline struct lock_class *hlock_class(struct held_lock *hlock)
{
        if (!hlock->class_idx) {
                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], lock_stats);

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, s64 time)
{
        if (time > lt->max)
                lt->max = time;

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

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

static inline void lock_time_add(struct lock_time *src, struct lock_time *dst)
{
        dst->min += src->min;
        dst->max += src->max;
        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(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(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 &get_cpu_var(lock_stats)[class - lock_classes];
}

static void put_lock_stats(struct lock_class_stats *stats)
{
        put_cpu_var(lock_stats);
}

static void lock_release_holdtime(struct held_lock *hlock)
{
        struct lock_class_stats *stats;
        s64 holdtime;

        if (!lock_stat)
                return;

        holdtime = sched_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);
        put_lock_stats(stats);
}
#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 list_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 list_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.
 */
#define iterate_chain_key(key1, key2) \
        (((key1) << MAX_LOCKDEP_KEYS_BITS) ^ \
        ((key1) >> (64-MAX_LOCKDEP_KEYS_BITS)) ^ \
        (key2))

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
# define RECLAIM_VERBOSE        1
#else
# define HARDIRQ_VERBOSE        0
# define SOFTIRQ_VERBOSE        0
# define RECLAIM_VERBOSE        0
#endif

#if VERBOSE || HARDIRQ_VERBOSE || SOFTIRQ_VERBOSE || RECLAIM_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 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);

        trace->max_entries = trace->nr_entries;

        nr_stack_trace_entries += trace->nr_entries;

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

                printk("BUG: MAX_STACK_TRACE_ENTRIES too low!\n");
                printk("turning off the locking correctness validator.\n");
                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;
unsigned int max_recursion_depth;

static unsigned int lockdep_dependency_gen_id;

static bool lockdep_dependency_visit(struct lock_class *source,
                                     unsigned int depth)
{
        if (!depth)
                lockdep_dependency_gen_id++;
        if (source->dep_gen_id == lockdep_dependency_gen_id)
                return true;
        source->dep_gen_id = lockdep_dependency_gen_id;
        return false;
}

#ifdef CONFIG_DEBUG_LOCKDEP
/*
 * We cannot printk in early bootup code. Not even early_printk()
 * might work. So we mark any initialization errors and printk
 * about it later on, in lockdep_info().
 */
static int lockdep_init_error;
static unsigned long lockdep_init_trace_data[20];
static struct stack_trace lockdep_init_trace = {
        .max_entries = ARRAY_SIZE(lockdep_init_trace_data),
        .entries = lockdep_init_trace_data,
};

/*
 * Various lockdep statistics:
 */
atomic_t chain_lookup_hits;
atomic_t chain_lookup_misses;
atomic_t hardirqs_on_events;
atomic_t hardirqs_off_events;
atomic_t redundant_hardirqs_on;
atomic_t redundant_hardirqs_off;
atomic_t softirqs_on_events;
atomic_t softirqs_off_events;
atomic_t redundant_softirqs_on;
atomic_t redundant_softirqs_off;
atomic_t nr_unused_locks;
atomic_t nr_cyclic_checks;
atomic_t nr_cyclic_check_recursions;
atomic_t nr_find_usage_forwards_checks;
atomic_t nr_find_usage_forwards_recursions;
atomic_t nr_find_usage_backwards_checks;
atomic_t nr_find_usage_backwards_recursions;
#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], usage[LOCK_USAGE_CHARS];
        const char *name;

        get_usage_chars(class, usage);

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

static void print_lock(struct held_lock *hlock)
{
        print_lock_name(hlock_class(hlock));
        printk(", at: ");
        print_ip_sym(hlock->acquire_ip);
}

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

        if (!depth) {
                printk("no locks held by %s/%d.\n", curr->comm, task_pid_nr(curr));
                return;
        }
        printk("%d lock%s held by %s/%d:\n",
                depth, depth > 1 ? "s" : "", curr->comm, task_pid_nr(curr));

        for (i = 0; i < depth; i++) {
                printk(" #%d: ", i);
                print_lock(curr->held_locks + i);
        }
}

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

        printk("%*s->", depth, "");
        print_lock_name(class);
        printk(" ops: %lu", class->ops);
        printk(" {\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(" at:\n");
                        print_stack_trace(class->usage_traces + bit, len);
                }
        }
        printk("%*s }\n", depth, "");

        printk("%*s ... key      at: ",depth,"");
        print_ip_sym((unsigned long)class->key);
}

/*
 * printk all lock dependencies starting at <entry>:
 */
static void __used
print_lock_dependencies(struct lock_class *class, int depth)
{
        struct lock_list *entry;

        if (lockdep_dependency_visit(class, depth))
                return;

        if (DEBUG_LOCKS_WARN_ON(depth >= 20))
                return;

        print_lock_class_header(class, depth);

        list_for_each_entry(entry, &class->locks_after, entry) {
                if (DEBUG_LOCKS_WARN_ON(!entry->class))
                        return;

                print_lock_dependencies(entry->class, depth + 1);

                printk("%*s ... acquired at:\n",depth,"");
                print_stack_trace(&entry->trace, 2);
                printk("\n");
        }
}

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

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:
 */
static int static_obj(void *obj)
{
        unsigned long start = (unsigned long) &_stext,
                      end   = (unsigned long) &_end,
                      addr  = (unsigned long) obj;
#ifdef CONFIG_SMP
        int i;
#endif

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

#ifdef CONFIG_SMP
        /*
         * percpu var?
         */
        for_each_possible_cpu(i) {
                start = (unsigned long) &__per_cpu_start + per_cpu_offset(i);
                end   = (unsigned long) &__per_cpu_start + PERCPU_ENOUGH_ROOM
                                        + per_cpu_offset(i);

                if ((addr >= start) && (addr < end))
                        return 1;
        }
#endif

        /*
         * module var?
         */
        return is_module_address(addr);
}

/*
 * To make lock name printouts unique, we calculate a unique
 * class->name_version generation counter:
 */
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;
}

/*
 * 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 inline struct lock_class *
look_up_lock_class(struct lockdep_map *lock, unsigned int subclass)
{
        struct lockdep_subclass_key *key;
        struct list_head *hash_head;
        struct lock_class *class;

#ifdef CONFIG_DEBUG_LOCKDEP
        /*
         * If the architecture calls into lockdep before initializing
         * the hashes then we'll warn about it later. (we cannot printk
         * right now)
         */
        if (unlikely(!lockdep_initialized)) {
                lockdep_init();
                lockdep_init_error = 1;
                save_stack_trace(&lockdep_init_trace);
        }
#endif

        /*
         * Static locks do not have their class-keys yet - for them the key
         * is the lock object itself:
         */
        if (unlikely(!lock->key))
                lock->key = (void *)lock;

        /*
         * 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 can walk the hash lockfree, because the hash only
         * grows, and we are careful when adding entries to the end:
         */
        list_for_each_entry(class, hash_head, hash_entry) {
                if (class->key == key) {
                        WARN_ON_ONCE(class->name != lock->name);
                        return class;
                }
        }

        return NULL;
}

/*
 * 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 inline struct lock_class *
register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force)
{
        struct lockdep_subclass_key *key;
        struct list_head *hash_head;
        struct lock_class *class;
        unsigned long flags;

        class = look_up_lock_class(lock, subclass);
        if (likely(class))
                return class;

        /*
         * Debug-check: all keys must be persistent!
         */
        if (!static_obj(lock->key)) {
                debug_locks_off();
                printk("INFO: trying to register non-static key.\n");
                printk("the code is fine but needs lockdep annotation.\n");
                printk("turning off the locking correctness validator.\n");
                dump_stack();

                return NULL;
        }

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

        raw_local_irq_save(flags);
        if (!graph_lock()) {
                raw_local_irq_restore(flags);
                return NULL;
        }
        /*
         * We have to do the hash-walk again, to avoid races
         * with another CPU:
         */
        list_for_each_entry(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()) {
                        raw_local_irq_restore(flags);
                        return NULL;
                }
                raw_local_irq_restore(flags);

                printk("BUG: MAX_LOCKDEP_KEYS too low!\n");
                printk("turning off the locking correctness validator.\n");
                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->lock_entry);
        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:
         */
        list_add_tail_rcu(&class->hash_entry, hash_head);
        /*
         * Add it to the global list of classes:
         */
        list_add_tail_rcu(&class->lock_entry, &all_lock_classes);

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

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

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

        if (!subclass || force)
                lock->class_cache = class;

        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;

                printk("BUG: MAX_LOCKDEP_ENTRIES too low!\n");
                printk("turning off the locking correctness validator.\n");
                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 *class, struct lock_class *this,
                            struct list_head *head, unsigned long ip, int distance)
{
        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;

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

        entry->class = this;
        entry->distance = distance;
        /*
         * Since we never remove from the dependency list, the list can
         * be walked lockless by other CPUs, it's only allocation
         * that must be protected by the spinlock. But this also means
         * we must make new entries visible only once writes to the
         * entry become visible - hence the RCU op:
         */
        list_add_tail_rcu(&entry->entry, head);

        return 1;
}

/*
 * Recursive, forwards-direction lock-dependency checking, used for
 * both noncyclic checking and for hardirq-unsafe/softirq-unsafe
 * checking.
 *
 * (to keep the stackframe of the recursive functions small we
 *  use these global variables, and we also mark various helper
 *  functions as noinline.)
 */
static struct held_lock *check_source, *check_target;

/*
 * 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, unsigned int depth)
{
        if (debug_locks_silent)
                return 0;
        printk("\n-> #%u", depth);
        print_lock_name(target->class);
        printk(":\n");
        print_stack_trace(&target->trace, 6);

        return 0;
}

/*
 * 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 task_struct *curr = current;

        if (!debug_locks_off_graph_unlock() || debug_locks_silent)
                return 0;

        printk("\n=======================================================\n");
        printk(  "[ INFO: possible circular locking dependency detected ]\n");
        print_kernel_version();
        printk(  "-------------------------------------------------------\n");
        printk("%s/%d is trying to acquire lock:\n",
                curr->comm, task_pid_nr(curr));
        print_lock(check_source);
        printk("\nbut task is already holding lock:\n");
        print_lock(check_target);
        printk("\nwhich lock already depends on the new lock.\n\n");
        printk("\nthe existing dependency chain (in reverse order) is:\n");

        print_circular_bug_entry(entry, depth);

        return 0;
}

static noinline int print_circular_bug_tail(void)
{
        struct task_struct *curr = current;
        struct lock_list this;

        if (debug_locks_silent)
                return 0;

        this.class = hlock_class(check_source);
        if (!save_trace(&this.trace))
                return 0;

        print_circular_bug_entry(&this, 0);

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

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

        return 0;
}

#define RECURSION_LIMIT 40

static int noinline print_infinite_recursion_bug(void)
{
        if (!debug_locks_off_graph_unlock())
                return 0;

        WARN_ON(1);

        return 0;
}

unsigned long __lockdep_count_forward_deps(struct lock_class *class,
                                           unsigned int depth)
{
        struct lock_list *entry;
        unsigned long ret = 1;

        if (lockdep_dependency_visit(class, depth))
                return 0;

        /*
         * Recurse this class's dependency list:
         */
        list_for_each_entry(entry, &class->locks_after, entry)
                ret += __lockdep_count_forward_deps(entry->class, depth + 1);

        return ret;
}

unsigned long lockdep_count_forward_deps(struct lock_class *class)
{
        unsigned long ret, flags;

        local_irq_save(flags);
        __raw_spin_lock(&lockdep_lock);
        ret = __lockdep_count_forward_deps(class, 0);
        __raw_spin_unlock(&lockdep_lock);
        local_irq_restore(flags);

        return ret;
}

unsigned long __lockdep_count_backward_deps(struct lock_class *class,
                                            unsigned int depth)
{
        struct lock_list *entry;
        unsigned long ret = 1;

        if (lockdep_dependency_visit(class, depth))
                return 0;
        /*
         * Recurse this class's dependency list:
         */
        list_for_each_entry(entry, &class->locks_before, entry)
                ret += __lockdep_count_backward_deps(entry->class, depth + 1);

        return ret;
}

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

        local_irq_save(flags);
        __raw_spin_lock(&lockdep_lock);
        ret = __lockdep_count_backward_deps(class, 0);
        __raw_spin_unlock(&lockdep_lock);
        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_class *source, unsigned int depth)
{
        struct lock_list *entry;

        if (lockdep_dependency_visit(source, depth))
                return 1;

        debug_atomic_inc(&nr_cyclic_check_recursions);
        if (depth > max_recursion_depth)
                max_recursion_depth = depth;
        if (depth >= RECURSION_LIMIT)
                return print_infinite_recursion_bug();
        /*
         * Check this lock's dependency list:
         */
        list_for_each_entry(entry, &source->locks_after, entry) {
                if (entry->class == hlock_class(check_target))
                        return print_circular_bug_header(entry, depth+1);
                debug_atomic_inc(&nr_cyclic_checks);
                if (!check_noncircular(entry->class, depth+1))
                        return print_circular_bug_entry(entry, depth+1);
        }
        return 1;
}

#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 enum lock_usage_bit find_usage_bit;
static struct lock_class *forwards_match, *backwards_match;

/*
 * Find a node in the forwards-direction dependency sub-graph starting
 * at <source> that matches <find_usage_bit>.
 *
 * Return 2 if such a node exists in the subgraph, and put that node
 * into <forwards_match>.
 *
 * Return 1 otherwise and keep <forwards_match> unchanged.
 * Return 0 on error.
 */
static noinline int
find_usage_forwards(struct lock_class *source, unsigned int depth)
{
        struct lock_list *entry;
        int ret;

        if (lockdep_dependency_visit(source, depth))
                return 1;

        if (depth > max_recursion_depth)
                max_recursion_depth = depth;
        if (depth >= RECURSION_LIMIT)
                return print_infinite_recursion_bug();

        debug_atomic_inc(&nr_find_usage_forwards_checks);
        if (source->usage_mask & (1 << find_usage_bit)) {
                forwards_match = source;
                return 2;
        }

        /*
         * Check this lock's dependency list:
         */
        list_for_each_entry(entry, &source->locks_after, entry) {
                debug_atomic_inc(&nr_find_usage_forwards_recursions);
                ret = find_usage_forwards(entry->class, depth+1);
                if (ret == 2 || ret == 0)
                        return ret;
        }
        return 1;
}

/*
 * Find a node in the backwards-direction dependency sub-graph starting
 * at <source> that matches <find_usage_bit>.
 *
 * Return 2 if such a node exists in the subgraph, and put that node
 * into <backwards_match>.
 *
 * Return 1 otherwise and keep <backwards_match> unchanged.
 * Return 0 on error.
 */
static noinline int
find_usage_backwards(struct lock_class *source, unsigned int depth)
{
        struct lock_list *entry;
        int ret;

        if (lockdep_dependency_visit(source, depth))
                return 1;

        if (!__raw_spin_is_locked(&lockdep_lock))
                return DEBUG_LOCKS_WARN_ON(1);

        if (depth > max_recursion_depth)
                max_recursion_depth = depth;
        if (depth >= RECURSION_LIMIT)
                return print_infinite_recursion_bug();

        debug_atomic_inc(&nr_find_usage_backwards_checks);
        if (source->usage_mask & (1 << find_usage_bit)) {
                backwards_match = source;
                return 2;
        }

        if (!source && debug_locks_off_graph_unlock()) {
                WARN_ON(1);
                return 0;
        }

        /*
         * Check this lock's dependency list:
         */
        list_for_each_entry(entry, &source->locks_before, entry) {
                debug_atomic_inc(&nr_find_usage_backwards_recursions);
                ret = find_usage_backwards(entry->class, depth+1);
                if (ret == 2 || ret == 0)
                        return ret;
        }
        return 1;
}

static int
print_bad_irq_dependency(struct task_struct *curr,
                         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;

        printk("\n======================================================\n");
        printk(  "[ INFO: %s-safe -> %s-unsafe lock order detected ]\n",
                irqclass, irqclass);
        print_kernel_version();
        printk(  "------------------------------------------------------\n");
        printk("%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);

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

        printk("\nbut this new dependency connects a %s-irq-safe lock:\n",
                irqclass);
        print_lock_name(backwards_match);
        printk("\n... which became %s-irq-safe at:\n", irqclass);

        print_stack_trace(backwards_match->usage_traces + bit1, 1);

        printk("\nto a %s-irq-unsafe lock:\n", irqclass);
        print_lock_name(forwards_match);
        printk("\n... which became %s-irq-unsafe at:\n", irqclass);
        printk("...");

        print_stack_trace(forwards_match->usage_traces + bit2, 1);

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

        printk("\nthe %s-irq-safe lock's dependencies:\n", irqclass);
        print_lock_dependencies(backwards_match, 0);

        printk("\nthe %s-irq-unsafe lock's dependencies:\n", irqclass);
        print_lock_dependencies(forwards_match, 0);

        printk("\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;

        find_usage_bit = bit_backwards;
        /* fills in <backwards_match> */
        ret = find_usage_backwards(hlock_class(prev), 0);
        if (!ret || ret == 1)
                return ret;

        find_usage_bit = bit_forwards;
        ret = find_usage_forwards(hlock_class(next), 0);
        if (!ret || ret == 1)
                return ret;
        /* ret == 2 */
        return print_bad_irq_dependency(curr, 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 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;

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

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

        printk("\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 lock_list *entry;
        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:
         */
        check_source = next;
        check_target = prev;
        if (!(check_noncircular(hlock_class(next), 0)))
                return print_circular_bug_tail();

        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 2;
                }
        }

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

        if (!ret)
                return 0;

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

        /*
         * Debugging printouts:
         */
        if (verbose(hlock_class(prev)) || verbose(hlock_class(next))) {
                graph_unlock();
                printk("\n new dependency: ");
                print_lock_name(hlock_class(prev));
                printk(" => ");
                print_lock_name(hlock_class(next));
                printk("\n");
                dump_stack();
                return graph_lock();
        }
        return 1;
}

/*
 * 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;

        /*
         * 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) {
                        if (!check_prev_add(curr, hlock, next, distance))
                                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;

        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];
}

/*
 * Look up a dependency chain. If the key is not present yet 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(struct task_struct *curr,
                                     struct held_lock *hlock,
                                     u64 chain_key)
{
        struct lock_class *class = hlock_class(hlock);
        struct list_head *hash_head = chainhashentry(chain_key);
        struct lock_chain *chain;
        struct held_lock *hlock_curr, *hlock_next;
        int i, j, n, cn;

        if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
                return 0;
        /*
         * We can walk it lock-free, because entries only get added
         * to the hash:
         */
        list_for_each_entry(chain, hash_head, entry) {
                if (chain->chain_key == chain_key) {
cache_hit:
                        debug_atomic_inc(&chain_lookup_hits);
                        if (very_verbose(class))
                                printk("\nhash chain already cached, key: "
                                        "%016Lx tail class: [%p] %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: [%p] %s\n",
                        (unsigned long long)chain_key, class->key, class->name);
        /*
         * Allocate a new chain entry from the static array, and add
         * it to the hash:
         */
        if (!graph_lock())
                return 0;
        /*
         * We have to walk the chain again locked - to avoid duplicates:
         */
        list_for_each_entry(chain, hash_head, entry) {
                if (chain->chain_key == chain_key) {
                        graph_unlock();
                        goto cache_hit;
                }
        }
        if (unlikely(nr_lock_chains >= MAX_LOCKDEP_CHAINS)) {
                if (!debug_locks_off_graph_unlock())
                        return 0;

                printk("BUG: MAX_LOCKDEP_CHAINS too low!\n");
                printk("turning off the locking correctness validator.\n");
                dump_stack();
                return 0;
        }
        chain = lock_chains + nr_lock_chains++;
        chain->chain_key = chain_key;
        chain->irq_context = hlock->irq_context;
        /* Find the first held_lock of current chain */
        hlock_next = hlock;
        for (i = curr->lockdep_depth - 1; i >= 0; i--) {
                hlock_curr = curr->held_locks + i;
                if (hlock_curr->irq_context != hlock_next->irq_context)
                        break;
                hlock_next = hlock;
        }
        i++;
        chain->depth = curr->lockdep_depth + 1 - i;
        cn = nr_chain_hlocks;
        while (cn + chain->depth <= MAX_LOCKDEP_CHAIN_HLOCKS) {
                n = cmpxchg(&nr_chain_hlocks, cn, cn + chain->depth);
                if (n == cn)
                        break;
                cn = n;
        }
        if (likely(cn + chain->depth <= MAX_LOCKDEP_CHAIN_HLOCKS)) {
                chain->base = cn;
                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;
        }
        list_add_tail_rcu(&chain->entry, hash_head);
        debug_atomic_inc(&chain_lookup_misses);
        inc_chains();

        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() returns with 1 it acquires
         * graph_lock for us)
         */
        if (!hlock->trylock && (hlock->check == 2) &&
            lookup_chain_cache(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(): */
                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, id;
        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();
                        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;
                }
                id = hlock->class_idx - 1;
                if (DEBUG_LOCKS_WARN_ON(id >= MAX_LOCKDEP_KEYS))
                        return;

                if (prev_hlock && (prev_hlock->irq_context !=
                                                        hlock->irq_context))
                        chain_key = 0;
                chain_key = iterate_chain_key(chain_key, id);
                prev_hlock = hlock;
        }
        if (chain_key != curr->curr_chain_key) {
                debug_locks_off();
                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 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;

        printk("\n=================================\n");
        printk(  "[ INFO: inconsistent lock state ]\n");
        print_kernel_version();
        printk(  "---------------------------------\n");

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

        printk("%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);

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

        printk("\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_class *other,
                        struct held_lock *this, int forwards,
                        const char *irqclass)
{
        if (!debug_locks_off_graph_unlock() || debug_locks_silent)
                return 0;

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

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

        printk("\nthe first lock's dependencies:\n");
        print_lock_dependencies(hlock_class(this), 0);

        printk("\nthe second lock's dependencies:\n");
        print_lock_dependencies(other, 0);

        printk("\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;

        find_usage_bit = bit;
        /* fills in <forwards_match> */
        ret = find_usage_forwards(hlock_class(this), 0);
        if (!ret || ret == 1)
                return ret;

        return print_irq_inversion_bug(curr, forwards_match, 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;

        find_usage_bit = bit;
        /* fills in <backwards_match> */
        ret = find_usage_backwards(hlock_class(this), 0);
        if (!ret || ret == 1)
                return ret;

        return print_irq_inversion_bug(curr, backwards_match, 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): ", curr->hardirq_enable_event);
        print_ip_sym(curr->hardirq_enable_ip);
        printk("hardirqs last disabled at (%u): ", curr->hardirq_disable_event);
        print_ip_sym(curr->hardirq_disable_ip);
        printk("softirqs last  enabled at (%u): ", curr->softirq_enable_event);
        print_ip_sym(curr->softirq_enable_ip);
        printk("softirqs last disabled at (%u): ", curr->softirq_disable_event);
        print_ip_sym(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;
}

static int RECLAIM_FS_verbose(struct lock_class *class)
{
#if RECLAIM_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 (!mark_lock(curr, hlock, usage_bit))
                        return 0;
        }

        return 1;
}

/*
 * Debugging helper: via this flag we know that we are in
 * 'early bootup code', and will warn about any invalid irqs-on event:
 */
static int early_boot_irqs_enabled;

void early_boot_irqs_off(void)
{
        early_boot_irqs_enabled = 0;
}

void early_boot_irqs_on(void)
{
        early_boot_irqs_enabled = 1;
}

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

        time_hardirqs_on(CALLER_ADDR0, ip);

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

        if (DEBUG_LOCKS_WARN_ON(unlikely(!early_boot_irqs_enabled)))
                return;

        if (unlikely(curr->hardirqs_enabled)) {
                debug_atomic_inc(&redundant_hardirqs_on);
                return;
        }
        /* we'll do an OFF -> ON transition: */
        curr->hardirqs_enabled = 1;

        if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
                return;
        if (DEBUG_LOCKS_WARN_ON(current->hardirq_context))
                return;
        /*
         * 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);
}
EXPORT_SYMBOL(trace_hardirqs_on_caller);

void trace_hardirqs_on(void)
{
        trace_hardirqs_on_caller(CALLER_ADDR0);
}
EXPORT_SYMBOL(trace_hardirqs_on);

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

        time_hardirqs_off(CALLER_ADDR0, ip);

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

        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);
}
EXPORT_SYMBOL(trace_hardirqs_off_caller);

void trace_hardirqs_off(void)
{
        trace_hardirqs_off_caller(CALLER_ADDR0);
}
EXPORT_SYMBOL(trace_hardirqs_off);

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

        if (unlikely(!debug_locks))
                return;

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

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

        /*
         * 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);
}

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

        if (unlikely(!debug_locks))
                return;

        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);
                DEBUG_LOCKS_WARN_ON(!softirq_count());
        } else
                debug_atomic_inc(&redundant_softirqs_off);
}

static void __lockdep_trace_alloc(gfp_t gfp_mask, unsigned long flags)
{
        struct task_struct *curr = current;

        if (unlikely(!debug_locks))
                return;

        /* no reclaim without waiting on it */
        if (!(gfp_mask & __GFP_WAIT))
                return;

        /* this guy won't enter reclaim */
        if ((curr->flags & PF_MEMALLOC) && !(gfp_mask & __GFP_NOMEMALLOC))
                return;

        /* We're only interested __GFP_FS allocations for now */
        if (!(gfp_mask & __GFP_FS))
                return;

        if (DEBUG_LOCKS_WARN_ON(irqs_disabled_flags(flags)))
                return;

        mark_held_locks(curr, RECLAIM_FS);
}

static void check_flags(unsigned long flags);

void lockdep_trace_alloc(gfp_t gfp_mask)
{
        unsigned long flags;

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

        raw_local_irq_save(flags);
        check_flags(flags);
        current->lockdep_recursion = 1;
        __lockdep_trace_alloc(gfp_mask, flags);
        current->lockdep_recursion = 0;
        raw_local_irq_restore(flags);
}

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;
                }
        }

        /*
         * We reuse the irq context infrastructure more broadly as a general
         * context checking code. This tests GFP_FS recursion (a lock taken
         * during reclaim for a GFP_FS allocation is held over a GFP_FS
         * allocation).
         */
        if (!hlock->trylock && (curr->lockdep_reclaim_gfp & __GFP_FS)) {
                if (hlock->read) {
                        if (!mark_lock(curr, hlock, LOCK_USED_IN_RECLAIM_FS_READ))
                                        return 0;
                } else {
                        if (!mark_lock(curr, hlock, LOCK_USED_IN_RECLAIM_FS))
                                        return 0;
                }
        }

        return 1;
}

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:
         */
        hlock->irq_context = 2*(curr->hardirq_context ? 1 : 0) +
                                curr->softirq_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

static inline
int mark_lock_irq(struct task_struct *curr, struct held_lock *this,
                enum lock_usage_bit new_bit)
{
        WARN_ON(1);
        return 1;
}

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

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

void lockdep_trace_alloc(gfp_t gfp_mask)
{
}

#endif

/*
 * 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 didnt 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)
{
        lock->class_cache = NULL;
#ifdef CONFIG_LOCK_STAT
        lock->cpu = raw_smp_processor_id();
#endif

        if (DEBUG_LOCKS_WARN_ON(!name)) {
                lock->name = "NULL";
                return;
        }

        lock->name = name;

        if (DEBUG_LOCKS_WARN_ON(!key))
                return;
        /*
         * Sanity check, the lock-class key must be persistent:
         */
        if (!static_obj(key)) {
                printk("BUG: key %p not in .data!\n", key);
                DEBUG_LOCKS_WARN_ON(1);
                return;
        }
        lock->key = key;

        if (unlikely(!debug_locks))
                return;

        if (subclass)
                register_lock_class(lock, subclass, 1);
}
EXPORT_SYMBOL_GPL(lockdep_init_map);

/*
 * This gets called for every mutex_lock*()/spin_lock*() operation.
 * We maintain the dependency maps and validate the locking attempt:
 */
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)
{
        struct task_struct *curr = current;
        struct lock_class *class = NULL;
        struct held_lock *hlock;
        unsigned int depth, id;
        int chain_head = 0;
        u64 chain_key;

        if (!prove_locking)
                check = 1;

        if (unlikely(!debug_locks))
                return 0;

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

        if (unlikely(subclass >= MAX_LOCKDEP_SUBCLASSES)) {
                debug_locks_off();
                printk("BUG: MAX_LOCKDEP_SUBCLASSES too low!\n");
                printk("turning off the locking correctness validator.\n");
                dump_stack();
                return 0;
        }

        if (!subclass)
                class = lock->class_cache;
        /*
         * Not cached yet or subclass?
         */
        if (unlikely(!class)) {
                class = register_lock_class(lock, subclass, 0);
                if (!class)
                        return 0;
        }
        debug_atomic_inc((atomic_t *)&class->ops);
        if (very_verbose(class)) {
                printk("\nacquire class [%p] %s", class->key, class->name);
                if (class->name_version > 1)
                        printk("#%d", class->name_version);
                printk("\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;
        if (DEBUG_LOCKS_WARN_ON(depth >= MAX_LOCK_DEPTH))
                return 0;

        hlock = curr->held_locks + depth;
        if (DEBUG_LOCKS_WARN_ON(!class))
                return 0;
        hlock->class_idx = class - lock_classes + 1;
        hlock->acquire_ip = ip;
        hlock->instance = lock;
        hlock->nest_lock = nest_lock;
        hlock->trylock = trylock;
        hlock->read = read;
        hlock->check = check;
        hlock->hardirqs_off = !!hardirqs_off;
#ifdef CONFIG_LOCK_STAT
        hlock->waittime_stamp = 0;
        hlock->holdtime_stamp = sched_clock();
#endif

        if (check == 2 && !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.
         */
        id = class - lock_classes;
        if (DEBUG_LOCKS_WARN_ON(id >= MAX_LOCKDEP_KEYS))
                return 0;

        chain_key = curr->curr_chain_key;
        if (!depth) {
                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, id);

        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();
                printk("BUG: MAX_LOCK_DEPTH too low!\n");
                printk("turning off the locking correctness validator.\n");
                dump_stack();
                return 0;
        }

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

        return 1;
}

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

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

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

        return 0;
}

/*
 * Common debugging checks for both nested and non-nested unlock:
 */
static int check_unlock(struct task_struct *curr, struct lockdep_map *lock,
                        unsigned long ip)
{
        if (unlikely(!debug_locks))
                return 0;
        if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
                return 0;

        if (curr->lockdep_depth <= 0)
                return print_unlock_inbalance_bug(curr, lock, ip);

        return 1;
}

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, *prev_hlock;
        struct lock_class *class;
        unsigned int depth;
        int i;

        depth = curr->lockdep_depth;
        if (DEBUG_LOCKS_WARN_ON(!depth))
                return 0;

        prev_hlock = NULL;
        for (i = depth-1; i >= 0; i--) {
                hlock = curr->held_locks + i;
                /*
                 * We must not cross into another context:
                 */
                if (prev_hlock && prev_hlock->irq_context != hlock->irq_context)
                        break;
                if (hlock->instance == lock)
                        goto found_it;
                prev_hlock = hlock;
        }
        return print_unlock_inbalance_bug(curr, lock, ip);

found_it:
        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->prev_chain_key;

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

        if (DEBUG_LOCKS_WARN_ON(curr->lockdep_depth != depth))
                return 0;
        return 1;
}

/*
 * Remove the lock to the list of currently held locks in a
 * potentially non-nested (out of order) manner. This is a
 * relatively rare operation, as all the unlock APIs default
 * to nested mode (which uses lock_release()):
 */
static int
lock_release_non_nested(struct task_struct *curr,
                        struct lockdep_map *lock, unsigned long ip)
{
        struct held_lock *hlock, *prev_hlock;
        unsigned int depth;
        int i;

        /*
         * Check whether the lock exists in the current stack
         * of held locks:
         */
        depth = curr->lockdep_depth;
        if (DEBUG_LOCKS_WARN_ON(!depth))
                return 0;

        prev_hlock = NULL;
        for (i = depth-1; i >= 0; i--) {
                hlock = curr->held_locks + i;
                /*
                 * We must not cross into another context:
                 */
                if (prev_hlock && prev_hlock->irq_context != hlock->irq_context)
                        break;
                if (hlock->instance == lock)
                        goto found_it;
                prev_hlock = hlock;
        }
        return print_unlock_inbalance_bug(curr, lock, ip);

found_it:
        lock_release_holdtime(hlock);

        /*
         * We have the right lock to unlock, 'hlock' points to it.
         * Now we remove it from the stack, and add back the other
         * entries (if any), recalculating the hash along the way:
         */
        curr->lockdep_depth = i;
        curr->curr_chain_key = hlock->prev_chain_key;

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

        if (DEBUG_LOCKS_WARN_ON(curr->lockdep_depth != depth - 1))
                return 0;
        return 1;
}

/*
 * Remove the lock to the list of currently held locks - this gets
 * called on mutex_unlock()/spin_unlock*() (or on a failed
 * mutex_lock_interruptible()). This is done for unlocks that nest
 * perfectly. (i.e. the current top of the lock-stack is unlocked)
 */
static int lock_release_nested(struct task_struct *curr,
                               struct lockdep_map *lock, unsigned long ip)
{
        struct held_lock *hlock;
        unsigned int depth;

        /*
         * Pop off the top of the lock stack:
         */
        depth = curr->lockdep_depth - 1;
        hlock = curr->held_locks + depth;

        /*
         * Is the unlock non-nested:
         */
        if (hlock->instance != lock)
                return lock_release_non_nested(curr, lock, ip);
        curr->lockdep_depth--;

        if (DEBUG_LOCKS_WARN_ON(!depth && (hlock->prev_chain_key != 0)))
                return 0;

        curr->curr_chain_key = hlock->prev_chain_key;

        lock_release_holdtime(hlock);

#ifdef CONFIG_DEBUG_LOCKDEP
        hlock->prev_chain_key = 0;
        hlock->class_idx = 0;
        hlock->acquire_ip = 0;
        hlock->irq_context = 0;
#endif
        return 1;
}

/*
 * Remove the lock to the list of currently held locks - this gets
 * called on mutex_unlock()/spin_unlock*() (or on a failed
 * mutex_lock_interruptible()). This is done for unlocks that nest
 * perfectly. (i.e. the current top of the lock-stack is unlocked)
 */
static void
__lock_release(struct lockdep_map *lock, int nested, unsigned long ip)
{
        struct task_struct *curr = current;

        if (!check_unlock(curr, lock, ip))
                return;

        if (nested) {
                if (!lock_release_nested(curr, lock, ip))
                        return;
        } else {
                if (!lock_release_non_nested(curr, lock, ip))
                        return;
        }

        check_chain_key(curr);
}

/*
 * Check whether we follow the irq-flags state precisely:
 */
static void check_flags(unsigned long flags)
{
#if defined(CONFIG_PROVE_LOCKING) && defined(CONFIG_DEBUG_LOCKDEP) && \
    defined(CONFIG_TRACE_IRQFLAGS)
        if (!debug_locks)
                return;

        if (irqs_disabled_flags(flags)) {
                if (DEBUG_LOCKS_WARN_ON(current->hardirqs_enabled)) {
                        printk("possible reason: unannotated irqs-off.\n");
                }
        } else {
                if (DEBUG_LOCKS_WARN_ON(!current->hardirqs_enabled)) {
                        printk("possible reason: unannotated irqs-on.\n");
                }
        }

        /*
         * We dont accurately track softirq state in e.g.
         * hardirq contexts (such as on 4KSTACKS), so only
         * check if not in hardirq contexts:
         */
        if (!hardirq_count()) {
                if (softirq_count())
                        DEBUG_LOCKS_WARN_ON(current->softirqs_enabled);
                else
                        DEBUG_LOCKS_WARN_ON(!current->softirqs_enabled);
        }

        if (!debug_locks)
                print_irqtrace_events(current);
#endif
}

void lock_set_class(struct lockdep_map *lock, const char *name,
                    struct lock_class_key *key, unsigned int subclass,
                    unsigned long ip)
{
        unsigned long flags;

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

        raw_local_irq_save(flags);
        current->lockdep_recursion = 1;
        check_flags(flags);
        if (__lock_set_class(lock, name, key, subclass, ip))
                check_chain_key(current);
        current->lockdep_recursion = 0;
        raw_local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(lock_set_class);

DEFINE_TRACE(lock_acquire);

/*
 * We are not always called with irqs disabled - do that here,
 * and also avoid lockdep recursion:
 */
void lock_acquire(struct lockdep_map *lock, unsigned int subclass,
                          int trylock, int read, int check,
                          struct lockdep_map *nest_lock, unsigned long ip)
{
        unsigned long flags;

        trace_lock_acquire(lock, subclass, trylock, read, check, nest_lock, ip);

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

        raw_local_irq_save(flags);
        check_flags(flags);

        current->lockdep_recursion = 1;
        __lock_acquire(lock, subclass, trylock, read, check,
                       irqs_disabled_flags(flags), nest_lock, ip);
        current->lockdep_recursion = 0;
        raw_local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(lock_acquire);

DEFINE_TRACE(lock_release);

void lock_release(struct lockdep_map *lock, int nested,
                          unsigned long ip)
{
        unsigned long flags;

        trace_lock_release(lock, nested, ip);

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

        raw_local_irq_save(flags);
        check_flags(flags);
        current->lockdep_recursion = 1;
        __lock_release(lock, nested, ip);
        current->lockdep_recursion = 0;
        raw_local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(lock_release);

void lockdep_set_current_reclaim_state(gfp_t gfp_mask)
{
        current->lockdep_reclaim_gfp = gfp_mask;
}

void lockdep_clear_current_reclaim_state(void)
{
        current->lockdep_reclaim_gfp = 0;
}

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

        printk("\n=================================\n");
        printk(  "[ BUG: bad contention detected! ]\n");
        printk(  "---------------------------------\n");
        printk("%s/%d is trying to contend lock (",
                curr->comm, task_pid_nr(curr));
        print_lockdep_cache(lock);
        printk(") at:\n");
        print_ip_sym(ip);
        printk("but there are no locks held!\n");
        printk("\nother info that might help us debug this:\n");
        lockdep_print_held_locks(curr);

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

        return 0;
}

static void
__lock_contended(struct lockdep_map *lock, unsigned long ip)
{
        struct task_struct *curr = current;
        struct held_lock *hlock, *prev_hlock;
        struct lock_class_stats *stats;
        unsigned int depth;
        int i, contention_point, contending_point;

        depth = curr->lockdep_depth;
        if (DEBUG_LOCKS_WARN_ON(!depth))
                return;

        prev_hlock = NULL;
        for (i = depth-1; i >= 0; i--) {
                hlock = curr->held_locks + i;
                /*
                 * We must not cross into another context:
                 */
                if (prev_hlock && prev_hlock->irq_context != hlock->irq_context)
                        break;
                if (hlock->instance == lock)
                        goto found_it;
                prev_hlock = hlock;
        }
        print_lock_contention_bug(curr, lock, ip);
        return;

found_it:
        hlock->waittime_stamp = sched_clock();

        contention_point = lock_point(hlock_class(hlock)->contention_point, ip);
        contending_point = lock_point(hlock_class(hlock)->contending_point,
                                      lock->ip);

        stats = get_lock_stats(hlock_class(hlock));
        if (contention_point < LOCKSTAT_POINTS)
                stats->contention_point[contention_point]++;
        if (contending_point < LOCKSTAT_POINTS)
                stats->contending_point[contending_point]++;
        if (lock->cpu != smp_processor_id())
                stats->bounces[bounce_contended + !!hlock->read]++;
        put_lock_stats(stats);
}

static void
__lock_acquired(struct lockdep_map *lock, unsigned long ip)
{
        struct task_struct *curr = current;
        struct held_lock *hlock, *prev_hlock;
        struct lock_class_stats *stats;
        unsigned int depth;
        u64 now;
        s64 waittime = 0;
        int i, cpu;

        depth = curr->lockdep_depth;
        if (DEBUG_LOCKS_WARN_ON(!depth))
                return;

        prev_hlock = NULL;
        for (i = depth-1; i >= 0; i--) {
                hlock = curr->held_locks + i;
                /*
                 * We must not cross into another context:
                 */
                if (prev_hlock && prev_hlock->irq_context != hlock->irq_context)
                        break;
                if (hlock->instance == lock)
                        goto found_it;
                prev_hlock = hlock;
        }
        print_lock_contention_bug(curr, lock, _RET_IP_);
        return;

found_it:
        cpu = smp_processor_id();
        if (hlock->waittime_stamp) {
                now = sched_clock();
                waittime = now - hlock->waittime_stamp;
                hlock->holdtime_stamp = now;
        }

        stats = get_lock_stats(hlock_class(hlock));
        if (waittime) {
                if (hlock->read)
                        lock_time_inc(&stats->read_waittime, waittime);
                else
                        lock_time_inc(&stats->write_waittime, waittime);
        }
        if (lock->cpu != cpu)
                stats->bounces[bounce_acquired + !!hlock->read]++;
        put_lock_stats(stats);

        lock->cpu = cpu;
        lock->ip = ip;
}

DEFINE_TRACE(lock_contended);

void lock_contended(struct lockdep_map *lock, unsigned long ip)
{
        unsigned long flags;

        trace_lock_contended(lock, ip);

        if (unlikely(!lock_stat))
                return;

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

        raw_local_irq_save(flags);
        check_flags(flags);
        current->lockdep_recursion = 1;
        __lock_contended(lock, ip);
        current->lockdep_recursion = 0;
        raw_local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(lock_contended);

DEFINE_TRACE(lock_acquired);

void lock_acquired(struct lockdep_map *lock, unsigned long ip)
{
        unsigned long flags;

        trace_lock_acquired(lock, ip);

        if (unlikely(!lock_stat))
                return;

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

        raw_local_irq_save(flags);
        check_flags(flags);
        current->lockdep_recursion = 1;
        __lock_acquired(lock, ip);
        current->lockdep_recursion = 0;
        raw_local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(lock_acquired);
#endif

/*
 * Used by the testsuite, sanitize the validator state
 * after a simulated failure:
 */

void lockdep_reset(void)
{
        unsigned long flags;
        int i;

        raw_local_irq_save(flags);
        current->curr_chain_key = 0;
        current->lockdep_depth = 0;
        current->lockdep_recursion = 0;
        memset(current->held_locks, 0, MAX_LOCK_DEPTH*sizeof(struct held_lock));
        nr_hardirq_chains = 0;
        nr_softirq_chains = 0;
        nr_process_chains = 0;
        debug_locks = 1;
        for (i = 0; i < CHAINHASH_SIZE; i++)
                INIT_LIST_HEAD(chainhash_table + i);
        raw_local_irq_restore(flags);
}

static void zap_class(struct lock_class *class)
{
        int i;

        /*
         * Remove all dependencies this lock is
         * involved in:
         */
        for (i = 0; i < nr_list_entries; i++) {
                if (list_entries[i].class == class)
                        list_del_rcu(&list_entries[i].entry);
        }
        /*
         * Unhash the class and remove it from the all_lock_classes list:
         */
        list_del_rcu(&class->hash_entry);
        list_del_rcu(&class->lock_entry);

        class->key = NULL;
}

static inline int within(const void *addr, void *start, unsigned long size)
{
        return addr >= start && addr < start + size;
}

void lockdep_free_key_range(void *start, unsigned long size)
{
        struct lock_class *class, *next;
        struct list_head *head;
        unsigned long flags;
        int i;
        int locked;

        raw_local_irq_save(flags);
        locked = graph_lock();

        /*
         * Unhash all classes that were created by this module:
         */
        for (i = 0; i < CLASSHASH_SIZE; i++) {
                head = classhash_table + i;
                if (list_empty(head))
                        continue;
                list_for_each_entry_safe(class, next, head, hash_entry) {
                        if (within(class->key, start, size))
                                zap_class(class);
                        else if (within(class->name, start, size))
                                zap_class(class);
                }
        }

        if (locked)
                graph_unlock();
        raw_local_irq_restore(flags);
}

void lockdep_reset_lock(struct lockdep_map *lock)
{
        struct lock_class *class, *next;
        struct list_head *head;
        unsigned long flags;
        int i, j;
        int locked;

        raw_local_irq_save(flags);

        /*
         * Remove all classes this lock might have:
         */
        for (j = 0; j < MAX_LOCKDEP_SUBCLASSES; j++) {
                /*
                 * If the class exists we look it up and zap it:
                 */
                class = look_up_lock_class(lock, j);
                if (class)
                        zap_class(class);
        }
        /*
         * Debug check: in the end all mapped classes should
         * be gone.
         */
        locked = graph_lock();
        for (i = 0; i < CLASSHASH_SIZE; i++) {
                head = classhash_table + i;
                if (list_empty(head))
                        continue;
                list_for_each_entry_safe(class, next, head, hash_entry) {
                        if (unlikely(class == lock->class_cache)) {
                                if (debug_locks_off_graph_unlock())
                                        WARN_ON(1);
                                goto out_restore;
                        }
                }
        }
        if (locked)
                graph_unlock();

out_restore:
        raw_local_irq_restore(flags);
}

void lockdep_init(void)
{
        int i;

        /*
         * Some architectures have their own start_kernel()
         * code which calls lockdep_init(), while we also
         * call lockdep_init() from the start_kernel() itself,
         * and we want to initialize the hashes only once:
         */
        if (lockdep_initialized)
                return;

        for (i = 0; i < CLASSHASH_SIZE; i++)
                INIT_LIST_HEAD(classhash_table + i);

        for (i = 0; i < CHAINHASH_SIZE; i++)
                INIT_LIST_HEAD(chainhash_table + i);

        lockdep_initialized = 1;
}

void __init lockdep_info(void)
{
        printk("Lock dependency validator: Copyright (c) 2006 Red Hat, Inc., Ingo Molnar\n");

        printk("... MAX_LOCKDEP_SUBCLASSES:  %lu\n", MAX_LOCKDEP_SUBCLASSES);
        printk("... MAX_LOCK_DEPTH:          %lu\n", MAX_LOCK_DEPTH);
        printk("... MAX_LOCKDEP_KEYS:        %lu\n", MAX_LOCKDEP_KEYS);
        printk("... CLASSHASH_SIZE:          %lu\n", CLASSHASH_SIZE);
        printk("... MAX_LOCKDEP_ENTRIES:     %lu\n", MAX_LOCKDEP_ENTRIES);
        printk("... MAX_LOCKDEP_CHAINS:      %lu\n", MAX_LOCKDEP_CHAINS);
        printk("... CHAINHASH_SIZE:          %lu\n", CHAINHASH_SIZE);

        printk(" memory used by lock dependency info: %lu kB\n",
                (sizeof(struct lock_class) * MAX_LOCKDEP_KEYS +
                sizeof(struct list_head) * CLASSHASH_SIZE +
                sizeof(struct lock_list) * MAX_LOCKDEP_ENTRIES +
                sizeof(struct lock_chain) * MAX_LOCKDEP_CHAINS +
                sizeof(struct list_head) * CHAINHASH_SIZE) / 1024);

        printk(" per task-struct memory footprint: %lu bytes\n",
                sizeof(struct held_lock) * MAX_LOCK_DEPTH);

#ifdef CONFIG_DEBUG_LOCKDEP
        if (lockdep_init_error) {
                printk("WARNING: lockdep init error! Arch code didn't call lockdep_init() early enough?\n");
                printk("Call stack leading to lockdep invocation was:\n");
                print_stack_trace(&lockdep_init_trace, 0);
        }
#endif
}

static void
print_freed_lock_bug(struct task_struct *curr, const void *mem_from,
                     const void *mem_to, struct held_lock *hlock)
{
        if (!debug_locks_off())
                return;
        if (debug_locks_silent)
                return;

        printk("\n=========================\n");
        printk(  "[ BUG: held lock freed! ]\n");
        printk(  "-------------------------\n");
        printk("%s/%d is freeing memory %p-%p, with a lock still held there!\n",
                curr->comm, task_pid_nr(curr), mem_from, mem_to-1);
        print_lock(hlock);
        lockdep_print_held_locks(curr);

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

static inline int not_in_range(const void* mem_from, unsigned long mem_len,
                                const void* lock_from, unsigned long lock_len)
{
        return lock_from + lock_len <= mem_from ||
                mem_from + mem_len <= lock_from;
}

/*
 * Called when kernel memory is freed (or unmapped), or if a lock
 * is destroyed or reinitialized - this code checks whether there is
 * any held lock in the memory range of <from> to <to>:
 */
void debug_check_no_locks_freed(const void *mem_from, unsigned long mem_len)
{
        struct task_struct *curr = current;
        struct held_lock *hlock;
        unsigned long flags;
        int i;

        if (unlikely(!debug_locks))
                return;

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

                if (not_in_range(mem_from, mem_len, hlock->instance,
                                        sizeof(*hlock->instance)))
                        continue;

                print_freed_lock_bug(curr, mem_from, mem_from + mem_len, hlock);
                break;
        }
        local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(debug_check_no_locks_freed);

static void print_held_locks_bug(struct task_struct *curr)
{
        if (!debug_locks_off())
                return;
        if (debug_locks_silent)
                return;

        printk("\n=====================================\n");
        printk(  "[ BUG: lock held at task exit time! ]\n");
        printk(  "-------------------------------------\n");
        printk("%s/%d is exiting with locks still held!\n",
                curr->comm, task_pid_nr(curr));
        lockdep_print_held_locks(curr);

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

void debug_check_no_locks_held(struct task_struct *task)
{
        if (unlikely(task->lockdep_depth > 0))
                print_held_locks_bug(task);
}

void debug_show_all_locks(void)
{
        struct task_struct *g, *p;
        int count = 10;
        int unlock = 1;

        if (unlikely(!debug_locks)) {
                printk("INFO: lockdep is turned off.\n");
                return;
        }
        printk("\nShowing all locks held in the system:\n");

        /*
         * Here we try to get the tasklist_lock as hard as possible,
         * if not successful after 2 seconds we ignore it (but keep
         * trying). This is to enable a debug printout even if a
         * tasklist_lock-holding task deadlocks or crashes.
         */
retry:
        if (!read_trylock(&tasklist_lock)) {
                if (count == 10)
                        printk("hm, tasklist_lock locked, retrying... ");
                if (count) {
                        count--;
                        printk(" #%d", 10-count);
                        mdelay(200);
                        goto retry;
                }
                printk(" ignoring it.\n");
                unlock = 0;
        } else {
                if (count != 10)
                        printk(KERN_CONT " locked it.\n");
        }

        do_each_thread(g, p) {
                /*
                 * It's not reliable to print a task's held locks
                 * if it's not sleeping (or if it's not the current
                 * task):
                 */
                if (p->state == TASK_RUNNING && p != current)
                        continue;
                if (p->lockdep_depth)
                        lockdep_print_held_locks(p);
                if (!unlock)
                        if (read_trylock(&tasklist_lock))
                                unlock = 1;
        } while_each_thread(g, p);

        printk("\n");
        printk("=============================================\n\n");

        if (unlock)
                read_unlock(&tasklist_lock);
}
EXPORT_SYMBOL_GPL(debug_show_all_locks);

/*
 * Careful: only use this function if you are sure that
 * the task cannot run in parallel!
 */
void __debug_show_held_locks(struct task_struct *task)
{
        if (unlikely(!debug_locks)) {
                printk("INFO: lockdep is turned off.\n");
                return;
        }
        lockdep_print_held_locks(task);
}
EXPORT_SYMBOL_GPL(__debug_show_held_locks);

void debug_show_held_locks(struct task_struct *task)
{
                __debug_show_held_locks(task);
}
EXPORT_SYMBOL_GPL(debug_show_held_locks);

void lockdep_sys_exit(void)
{
        struct task_struct *curr = current;

        if (unlikely(curr->lockdep_depth)) {
                if (!debug_locks_off())
                        return;
                printk("\n================================================\n");
                printk(  "[ BUG: lock held when returning to user space! ]\n");
                printk(  "------------------------------------------------\n");
                printk("%s/%d is leaving the kernel with locks still held!\n",
                                curr->comm, curr->pid);
                lockdep_print_held_locks(curr);
        }
}