/*
 * 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.
 */
#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 <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_contention_point(struct lock_class *class, unsigned long ip)
{
        int i;

        for (i = 0; i < ARRAY_SIZE(class->contention_point); i++) {
                if (class->contention_point[i] == 0) {
                        class->contention_point[i] = ip;
                        break;
                }
                if (class->contention_point[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];

                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));
}

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
#else
# define HARDIRQ_VERBOSE        0
# define SOFTIRQ_VERBOSE        0
#endif

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

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

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

static 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;
# define debug_atomic_inc(ptr)          atomic_inc(ptr)
# define debug_atomic_dec(ptr)          atomic_dec(ptr)
# define debug_atomic_read(ptr)         atomic_read(ptr)
#else
# define debug_atomic_inc(ptr)          do { } while (0)
# define debug_atomic_dec(ptr)          do { } while (0)
# define debug_atomic_read(ptr)         0
#endif

/*
 * Locking printouts:
 */

static const char *usage_str[] =
{
        [LOCK_USED] =                   "initial-use ",
        [LOCK_USED_IN_HARDIRQ] =        "in-hardirq-W",
        [LOCK_USED_IN_SOFTIRQ] =        "in-softirq-W",
        [LOCK_ENABLED_SOFTIRQS] =       "softirq-on-W",
        [LOCK_ENABLED_HARDIRQS] =       "hardirq-on-W",
        [LOCK_USED_IN_HARDIRQ_READ] =   "in-hardirq-R",
        [LOCK_USED_IN_SOFTIRQ_READ] =   "in-softirq-R",
        [LOCK_ENABLED_SOFTIRQS_READ] =  "softirq-on-R",
        [LOCK_ENABLED_HARDIRQS_READ] =  "hardirq-on-R",
};

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

void
get_usage_chars(struct lock_class *class, char *c1, char *c2, char *c3, char *c4)
{
        *c1 = '.', *c2 = '.', *c3 = '.', *c4 = '.';

        if (class->usage_mask & LOCKF_USED_IN_HARDIRQ)
                *c1 = '+';
        else
                if (class->usage_mask & LOCKF_ENABLED_HARDIRQS)
                        *c1 = '-';

        if (class->usage_mask & LOCKF_USED_IN_SOFTIRQ)
                *c2 = '+';
        else
                if (class->usage_mask & LOCKF_ENABLED_SOFTIRQS)
                        *c2 = '-';

        if (class->usage_mask & LOCKF_ENABLED_HARDIRQS_READ)
                *c3 = '-';
        if (class->usage_mask & LOCKF_USED_IN_HARDIRQ_READ) {
                *c3 = '+';
                if (class->usage_mask & LOCKF_ENABLED_HARDIRQS_READ)
                        *c3 = '?';
        }

        if (class->usage_mask & LOCKF_ENABLED_SOFTIRQS_READ)
                *c4 = '-';
        if (class->usage_mask & LOCKF_USED_IN_SOFTIRQ_READ) {
                *c4 = '+';
                if (class->usage_mask & LOCKF_ENABLED_SOFTIRQS_READ)
                        *c4 = '?';
        }
}

static void print_lock_name(struct lock_class *class)
{
        char str[KSYM_NAME_LEN], c1, c2, c3, c4;
        const char *name;

        get_usage_chars(class, &c1, &c2, &c3, &c4);

        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("){%c%c%c%c}", c1, c2, c3, c4);
}

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 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");
                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");
                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 int
check_prev_add_irq(struct task_struct *curr, struct held_lock *prev,
                struct held_lock *next)
{
        /*
         * 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, LOCK_USED_IN_HARDIRQ,
                                        LOCK_ENABLED_HARDIRQS, "hard"))
                return 0;

        /*
         * 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, LOCK_USED_IN_HARDIRQ_READ,
                                        LOCK_ENABLED_HARDIRQS, "hard-read"))
                return 0;

        /*
         * Prove that the new dependency does not connect a softirq-safe
         * lock with a softirq-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, LOCK_USED_IN_SOFTIRQ,
                                        LOCK_ENABLED_SOFTIRQS, "soft"))
                return 0;
        /*
         * Prove that the new dependency does not connect a softirq-safe-read
         * lock with a softirq-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, LOCK_USED_IN_SOFTIRQ_READ,
                                        LOCK_ENABLED_SOFTIRQS, "soft"))
                return 0;

        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");
                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-irq-unsafe lock in the past:\n", irqclass);
        else
                printk("but this lock was taken by another, %s-irq-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;
}

#define STRICT_READ_CHECKS      1

static int mark_lock_irq(struct task_struct *curr, struct held_lock *this,
                enum lock_usage_bit new_bit)
{
        int ret = 1;

        switch(new_bit) {
        case LOCK_USED_IN_HARDIRQ:
                if (!valid_state(curr, this, new_bit, LOCK_ENABLED_HARDIRQS))
                        return 0;
                if (!valid_state(curr, this, new_bit,
                                 LOCK_ENABLED_HARDIRQS_READ))
                        return 0;
                /*
                 * just marked it hardirq-safe, check that this lock
                 * took no hardirq-unsafe lock in the past:
                 */
                if (!check_usage_forwards(curr, this,
                                          LOCK_ENABLED_HARDIRQS, "hard"))
                        return 0;
#if STRICT_READ_CHECKS
                /*
                 * just marked it hardirq-safe, check that this lock
                 * took no hardirq-unsafe-read lock in the past:
                 */
                if (!check_usage_forwards(curr, this,
                                LOCK_ENABLED_HARDIRQS_READ, "hard-read"))
                        return 0;
#endif
                if (hardirq_verbose(hlock_class(this)))
                        ret = 2;
                break;
        case LOCK_USED_IN_SOFTIRQ:
                if (!valid_state(curr, this, new_bit, LOCK_ENABLED_SOFTIRQS))
                        return 0;
                if (!valid_state(curr, this, new_bit,
                                 LOCK_ENABLED_SOFTIRQS_READ))
                        return 0;
                /*
                 * just marked it softirq-safe, check that this lock
                 * took no softirq-unsafe lock in the past:
                 */
                if (!check_usage_forwards(curr, this,
                                          LOCK_ENABLED_SOFTIRQS, "soft"))
                        return 0;
#if STRICT_READ_CHECKS
                /*
                 * just marked it softirq-safe, check that this lock
                 * took no softirq-unsafe-read lock in the past:
                 */
                if (!check_usage_forwards(curr, this,
                                LOCK_ENABLED_SOFTIRQS_READ, "soft-read"))