lockdep.c

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/*
 * kernel/lockdep.c
 *
 * Runtime locking correctness validator
 *
 * Started by Ingo Molnar:
 *
 *  Copyright (C) 2006,2007 Red Hat, Inc., Ingo Molnar <[email protected]>
 *  Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra <[email protected]>
 *
 * 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 <linux/bitops.h>
#include <linux/gfp.h>
#include <linux/kmemcheck.h>

#include <asm/sections.h>

#include "lockdep_internals.h"

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

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

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

/*
 * lockdep_lock: protects the lockdep graph, the hashes and the
 *               class/list/hash allocators.
 *
 * This is one of the rare exceptions where it's justified
 * to use a raw spinlock - we really dont want the spinlock
 * code to recurse back into the lockdep code...
 */
static arch_spinlock_t lockdep_lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;

static int graph_lock(void)
{
    arch_spin_lock(&lockdep_lock);
    /*
     * Make sure that if another CPU detected a bug while
     * walking the graph we dont change it (while the other
     * CPU is busy printing out stuff with the graph lock
     * dropped already)
     */
    if (!debug_locks) {
        arch_spin_unlock(&lockdep_lock);
        return 0;
    }
    /* prevent any recursions within lockdep from causing deadlocks */
    current->lockdep_recursion++;
    return 1;
}

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

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

/*
 * Turn lock debugging off and return with 0 if it was off already,
 * and also release the graph lock:
 */
static inline int debug_locks_off_graph_unlock(void)
{
    int ret = debug_locks_off();

    arch_spin_unlock(&lockdep_lock);

    return ret;
}

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) {
        /*
         * Someone passed in garbage, we give up.
         */
        DEBUG_LOCKS_WARN_ON(1);
        return NULL;
    }
    return lock_classes + hlock->class_idx - 1;
}

#ifdef CONFIG_LOCK_STAT
static DEFINE_PER_CPU(struct lock_class_stats[MAX_LOCKDEP_KEYS],
              cpu_lock_stats);

static inline u64 lockstat_clock(void)
{
    return local_clock();
}

static int lock_point(unsigned long points[], unsigned long ip)
{
    int i;

    for (i = 0; i < LOCKSTAT_POINTS; i++) {
        if (points[i] == 0) {
            points[i] = ip;
            break;
        }
        if (points[i] == ip)
            break;
    }

    return i;
}

static void lock_time_inc(struct lock_time *lt, u64 time)
{
    if (time > lt->max)
        lt->max = time;

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

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

static inline void lock_time_add(struct lock_time *src, struct lock_time *dst)
{
    if (!src->nr)
        return;

    if (src->max > dst->max)
        dst->max = src->max;

    if (src->min < dst->min || !dst->nr)
        dst->min = src->min;

    dst->total += src->total;
    dst->nr += src->nr;
}

struct lock_class_stats lock_stats(struct lock_class *class)
{
    struct lock_class_stats stats;
    int cpu, i;

    memset(&stats, 0, sizeof(struct lock_class_stats));
    for_each_possible_cpu(cpu) {
        struct lock_class_stats *pcs =
            &per_cpu(cpu_lock_stats, cpu)[class - lock_classes];

        for (i = 0; i < ARRAY_SIZE(stats.contention_point); i++)
            stats.contention_point[i] += pcs->contention_point[i];

        for (i = 0; i < ARRAY_SIZE(stats.contending_point); i++)
            stats.contending_point[i] += pcs->contending_point[i];

        lock_time_add(&pcs->read_waittime, &stats.read_waittime);
        lock_time_add(&pcs->write_waittime, &stats.write_waittime);

        lock_time_add(&pcs->read_holdtime, &stats.read_holdtime);
        lock_time_add(&pcs->write_holdtime, &stats.write_holdtime);

        for (i = 0; i < ARRAY_SIZE(stats.bounces); i++)
            stats.bounces[i] += pcs->bounces[i];
    }

    return stats;
}

void clear_lock_stats(struct lock_class *class)
{
    int cpu;

    for_each_possible_cpu(cpu) {
        struct lock_class_stats *cpu_stats =
            &per_cpu(cpu_lock_stats, cpu)[class - lock_classes];

        memset(cpu_stats, 0, sizeof(struct lock_class_stats));
    }
    memset(class->contention_point, 0, sizeof(class->contention_point));
    memset(class->contending_point, 0, sizeof(class->contending_point));
}

static struct lock_class_stats *get_lock_stats(struct lock_class *class)
{
    return &get_cpu_var(cpu_lock_stats)[class - lock_classes];
}

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

static void lock_release_holdtime(struct held_lock *hlock)
{
    struct lock_class_stats *stats;
    u64 holdtime;

    if (!lock_stat)
        return;

    holdtime = lockstat_clock() - hlock->holdtime_stamp;

    stats = get_lock_stats(hlock_class(hlock));
    if (hlock->read)
        lock_time_inc(&stats->read_holdtime, holdtime);
    else
        lock_time_inc(&stats->write_holdtime, holdtime);
    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);

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

    trace->max_entries = trace->nr_entries;

    nr_stack_trace_entries += trace->nr_entries;

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

        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;

#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 const char *lock_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:
 */
DEFINE_PER_CPU(struct lockdep_stats, lockdep_stats);
#endif

/*
 * Locking printouts:
 */

#define __USAGE(__STATE)                        \
    [LOCK_USED_IN_##__STATE] = "IN-"__stringify(__STATE)"-W",   \
    [LOCK_ENABLED_##__STATE] = __stringify(__STATE)"-ON-W",     \
    [LOCK_USED_IN_##__STATE##_READ] = "IN-"__stringify(__STATE)"-R",\
    [LOCK_ENABLED_##__STATE##_READ] = __stringify(__STATE)"-ON-R",

static const char *usage_str[] =
{
#define LOCKDEP_STATE(__STATE) __USAGE(__STATE)
#include "lockdep_states.h"
#undef LOCKDEP_STATE
    [LOCK_USED] = "INITIAL USE",
};

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

static inline unsigned long lock_flag(enum lock_usage_bit bit)
{
    return 1UL << bit;
}

static char get_usage_char(struct lock_class *class, enum lock_usage_bit bit)
{
    char c = '.';

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

    return c;
}

void get_usage_chars(struct lock_class *class, char usage[LOCK_USAGE_CHARS])
{
    int i = 0;

#define LOCKDEP_STATE(__STATE)                      \
    usage[i++] = get_usage_char(class, LOCK_USED_IN_##__STATE); \
    usage[i++] = get_usage_char(class, LOCK_USED_IN_##__STATE##_READ);
#include "lockdep_states.h"
#undef LOCKDEP_STATE

    usage[i] = '\0';
}

static void __print_lock_name(struct lock_class *class)
{
    char str[KSYM_NAME_LEN];
    const char *name;

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

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

    get_usage_chars(class, usage);

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

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

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

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

    if (arch_is_kernel_data(addr))
        return 1;

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

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

/*
 * 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;
        lock_init_error = lock->name;
        save_stack_trace(&lockdep_init_trace);
    }
#endif

    if (unlikely(subclass >= MAX_LOCKDEP_SUBCLASSES)) {
        debug_locks_off();
        printk(KERN_ERR
            "BUG: looking up invalid subclass: %u\n", subclass);
        printk(KERN_ERR
            "turning off the locking correctness validator.\n");
        dump_stack();
        return NULL;
    }

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

    return NULL;
}

/*
 * 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))
        goto out_set_class_cache;

    /*
     * 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);

out_set_class_cache:
    if (!subclass || force)
        lock->class_cache[0] = class;
    else if (subclass < NR_LOCKDEP_CACHING_CLASSES)
        lock->class_cache[subclass] = class;

    /*
     * Hash collision, did we smoke some? We found a class with a matching
     * hash but the subclass -- which is hashed in -- didn't match.
     */
    if (DEBUG_LOCKS_WARN_ON(class->subclass != subclass))
        return NULL;

    return class;
}

#ifdef CONFIG_PROVE_LOCKING
/*
 * Allocate a lockdep entry. (assumes the graph_lock held, returns
 * with NULL on failure)
 */
static struct lock_list *alloc_list_entry(void)
{
    if (nr_list_entries >= MAX_LOCKDEP_ENTRIES) {
        if (!debug_locks_off_graph_unlock())
            return NULL;

        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 stack_trace *trace)
{
    struct lock_list *entry;
    /*
     * Lock not present yet - get a new dependency struct and
     * add it to the list:
     */
    entry = alloc_list_entry();
    if (!entry)
        return 0;

    entry->class = this;
    entry->distance = distance;
    entry->trace = *trace;
    /*
     * 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;
}

/*
 * For good efficiency of modular, we use power of 2
 */
#define MAX_CIRCULAR_QUEUE_SIZE     4096UL
#define CQ_MASK             (MAX_CIRCULAR_QUEUE_SIZE-1)

/*
 * The circular_queue and helpers is used to implement the
 * breadth-first search(BFS)algorithem, by which we can build
 * the shortest path from the next lock to be acquired to the
 * previous held lock if there is a circular between them.
 */
struct circular_queue {
    unsigned long element[MAX_CIRCULAR_QUEUE_SIZE];
    unsigned int  front, rear;
};

static struct circular_queue lock_cq;

unsigned int max_bfs_queue_depth;

static unsigned int lockdep_dependency_gen_id;

static inline void __cq_init(struct circular_queue *cq)
{
    cq->front = cq->rear = 0;
    lockdep_dependency_gen_id++;
}

static inline int __cq_empty(struct circular_queue *cq)
{
    return (cq->front == cq->rear);
}

static inline int __cq_full(struct circular_queue *cq)
{
    return ((cq->rear + 1) & CQ_MASK) == cq->front;
}

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

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

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

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

static inline unsigned int  __cq_get_elem_count(struct circular_queue *cq)
{
    return (cq->rear - cq->front) & CQ_MASK;
}

static inline void mark_lock_accessed(struct lock_list *lock,
                    struct lock_list *parent)
{
    unsigned long nr;

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

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

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

static inline struct lock_list *get_lock_parent(struct lock_list *child)
{
    return child->parent;
}

static inline int get_lock_depth(struct lock_list *child)
{
    int depth = 0;
    struct lock_list *parent;

    while ((parent = get_lock_parent(child))) {
        child = parent;
        depth++;
    }
    return depth;
}

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

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

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

    if (list_empty(head))
        goto exit;

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

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

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

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

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

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

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

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

}

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

}

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

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

    return 0;
}

static void
print_circular_lock_scenario(struct held_lock *src,
                 struct held_lock *tgt,
                 struct lock_list *prt)
{
    struct lock_class *source = hlock_class(src);
    struct lock_class *target = hlock_class(tgt);
    struct lock_class *parent = prt->class;

    /*
     * A direct locking problem where unsafe_class lock is taken
     * directly by safe_class lock, then all we need to show
     * is the deadlock scenario, as it is obvious that the
     * unsafe lock is taken under the safe lock.
     *
     * But if there is a chain instead, where the safe lock takes
     * an intermediate lock (middle_class) where this lock is
     * not the same as the safe lock, then the lock chain is
     * used to describe the problem. Otherwise we would need
     * to show a different CPU case for each link in the chain
     * from the safe_class lock to the unsafe_class lock.
     */
    if (parent != source) {
        printk("Chain exists of:\n  ");
        __print_lock_name(source);
        printk(" --> ");
        __print_lock_name(parent);
        printk(" --> ");
        __print_lock_name(target);
        printk("\n\n");
    }

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

/*
 * When a circular dependency is detected, print the
 * header first:
 */
static noinline int
print_circular_bug_header(struct lock_list *entry, unsigned int depth,
            struct held_lock *check_src,
            struct held_lock *check_tgt)
{
    struct task_struct *curr = current;

    if (debug_locks_silent)
        return 0;

    printk("\n");
    printk("======================================================\n");
    printk("[ INFO: possible circular locking dependency detected ]\n");
    print_kernel_ident();
    printk("-------------------------------------------------------\n");
    printk("%s/%d is trying to acquire lock:\n",
        curr->comm, task_pid_nr(curr));
    print_lock(check_src);
    printk("\nbut task is already holding lock:\n");
    print_lock(check_tgt);
    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 inline int class_equal(struct lock_list *entry, void *data)
{
    return entry->class == data;
}

static noinline int print_circular_bug(struct lock_list *this,
                struct lock_list *target,
                struct held_lock *check_src,
                struct held_lock *check_tgt)
{
    struct task_struct *curr = current;
    struct lock_list *parent;
    struct lock_list *first_parent;
    int depth;

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

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

    depth = get_lock_depth(target);

    print_circular_bug_header(target, depth, check_src, check_tgt);

    parent = get_lock_parent(target);
    first_parent = parent;

    while (parent) {
        print_circular_bug_entry(parent, --depth);
        parent = get_lock_parent(parent);
    }

    printk("\nother info that might help us debug this:\n\n");
    print_circular_lock_scenario(check_src, check_tgt,
                     first_parent);

    lockdep_print_held_locks(curr);

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

    return 0;
}

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

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

    return 0;
}

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

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

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

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

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

    local_irq_save(flags);
    arch_spin_lock(&lockdep_lock);
    ret = __lockdep_count_forward_deps(&this);
    arch_spin_unlock(&lockdep_lock);
    local_irq_restore(flags);

    return ret;
}

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

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

    return count;
}

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

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

    local_irq_save(flags);
    arch_spin_lock(&lockdep_lock);
    ret = __lockdep_count_backward_deps(&this);
    arch_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_list *root, struct lock_class *target,
        struct lock_list **target_entry)
{
    int result;

    debug_atomic_inc(nr_cyclic_checks);

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

    return result;
}

#if defined(CONFIG_TRACE_IRQFLAGS) && defined(CONFIG_PROVE_LOCKING)
/*
 * Forwards and backwards subgraph searching, for the purposes of
 * proving that two subgraphs can be connected by a new dependency
 * without creating any illegal irq-safe -> irq-unsafe lock dependency.
 */

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



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

    debug_atomic_inc(nr_find_usage_forwards_checks);

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

    return result;
}

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

    debug_atomic_inc(nr_find_usage_backwards_checks);

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

    return result;
}

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

    printk("%*s->", depth, "");
    print_lock_name(class);
    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 the shortest lock dependencies from @start to @end in reverse order:
 */
static void __used
print_shortest_lock_dependencies(struct lock_list *leaf,
                struct lock_list *root)
{
    struct lock_list *entry = leaf;
    int depth;

    /*compute depth from generated tree by BFS*/
    depth = get_lock_depth(leaf);

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

        if (depth == 0 && (entry != root)) {
            printk("lockdep:%s bad path found in chain graph\n", __func__);
            break;
        }

        entry = get_lock_parent(entry);
        depth--;
    } while (entry && (depth >= 0));

    return;
}

static void
print_irq_lock_scenario(struct lock_list *safe_entry,
            struct lock_list *unsafe_entry,
            struct lock_class *prev_class,
            struct lock_class *next_class)
{
    struct lock_class *safe_class = safe_entry->class;
    struct lock_class *unsafe_class = unsafe_entry->class;
    struct lock_class *middle_class = prev_class;

    if (middle_class == safe_class)
        middle_class = next_class;

    /*
     * A direct locking problem where unsafe_class lock is taken
     * directly by safe_class lock, then all we need to show
     * is the deadlock scenario, as it is obvious that the
     * unsafe lock is taken under the safe lock.
     *
     * But if there is a chain instead, where the safe lock takes
     * an intermediate lock (middle_class) where this lock is
     * not the same as the safe lock, then the lock chain is
     * used to describe the problem. Otherwise we would need
     * to show a different CPU case for each link in the chain
     * from the safe_class lock to the unsafe_class lock.
     */
    if (middle_class != unsafe_class) {
        printk("Chain exists of:\n  ");
        __print_lock_name(safe_class);
        printk(" --> ");
        __print_lock_name(middle_class);
        printk(" --> ");
        __print_lock_name(unsafe_class);
        printk("\n\n");
    }

    printk(" Possible interrupt unsafe locking scenario:\n\n");
    printk("       CPU0                    CPU1\n");
    printk("       ----                    ----\n");
    printk("  lock(");
    __print_lock_name(unsafe_class);
    printk(");\n");
    printk("                               local_irq_disable();\n");
    printk("                               lock(");
    __print_lock_name(safe_class);
    printk(");\n");
    printk("                               lock(");
    __print_lock_name(middle_class);
    printk(");\n");
    printk("  <Interrupt>\n");
    printk("    lock(");
    __print_lock_name(safe_class);
    printk(");\n");
    printk("\n *** DEADLOCK ***\n\n");
}

static int
print_bad_irq_dependency(struct task_struct *curr,
             struct lock_list *prev_root,
             struct lock_list *next_root,
             struct lock_list *backwards_entry,
             struct lock_list *forwards_entry,
             struct held_lock *prev,
             struct held_lock *next,
             enum lock_usage_bit bit1,
             enum lock_usage_bit bit2,
             const char *irqclass)
{
    if (!debug_locks_off_graph_unlock() || debug_locks_silent)
        return 0;

    printk("\n");
    printk("======================================================\n");
    printk("[ INFO: %s-safe -> %s-unsafe lock order detected ]\n",
        irqclass, irqclass);
    print_kernel_ident();
    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_entry->class);
    printk("\n... which became %s-irq-safe at:\n", irqclass);

    print_stack_trace(backwards_entry->class->usage_traces + bit1, 1);

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

    print_stack_trace(forwards_entry->class->usage_traces + bit2, 1);

    printk("\nother info that might help us debug this:\n\n");
    print_irq_lock_scenario(backwards_entry, forwards_entry,
                hlock_class(prev), hlock_class(next));

    lockdep_print_held_locks(curr);

    printk("\nthe dependencies between %s-irq-safe lock", irqclass);
    printk(" and the holding lock:\n");
    if (!save_trace(&prev_root->trace))
        return 0;
    print_shortest_lock_dependencies(backwards_entry, prev_root);

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

    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;
    struct lock_list this, that;
    struct lock_list *uninitialized_var(target_entry);
    struct lock_list *uninitialized_var(target_entry1);

    this.parent = NULL;

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

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

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

static const char *state_names[] = {
#define LOCKDEP_STATE(__STATE) \
    __stringify(__STATE),
#include "lockdep_states.h"
#undef LOCKDEP_STATE
};

static const char *state_rnames[] = {
#define LOCKDEP_STATE(__STATE) \
    __stringify(__STATE)"-READ",
#include "lockdep_states.h"
#undef LOCKDEP_STATE
};

static inline const char *state_name(enum lock_usage_bit bit)
{
    return (bit & 1) ? state_rnames[bit >> 2] : state_names[bit >> 2];
}

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

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

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

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

    bit++; /* _READ */

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

    return 1;
}

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

    return 1;
}

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

#else

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

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

#endif

static void
print_deadlock_scenario(struct held_lock *nxt,
                 struct held_lock *prv)
{
    struct lock_class *next = hlock_class(nxt);
    struct lock_class *prev = hlock_class(prv);

    printk(" Possible unsafe locking scenario:\n\n");
    printk("       CPU0\n");
    printk("       ----\n");
    printk("  lock(");
    __print_lock_name(prev);
    printk(");\n");
    printk("  lock(");
    __print_lock_name(next);
    printk(");\n");
    printk("\n *** DEADLOCK ***\n\n");
    printk(" May be due to missing lock nesting notation\n\n");
}

static int
print_deadlock_bug(struct task_struct *curr, struct held_lock *prev,
           struct held_lock *next)
{
    if (!debug_locks_off_graph_unlock() || debug_locks_silent)
        return 0;

    printk("\n");
    printk("=============================================\n");
    printk("[ INFO: possible recursive locking detected ]\n");
    print_kernel_ident();
    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");
    print_deadlock_scenario(next, prev);
    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, int trylock_loop)
{
    struct lock_list *entry;
    int ret;
    struct lock_list this;
    struct lock_list *uninitialized_var(target_entry);
    /*
     * Static variable, serialized by the graph_lock().
     *
     * We use this static variable to save the stack trace in case
     * we call into this function multiple times due to encountering
     * trylocks in the held lock stack.
     */
    static struct stack_trace trace;

    /*
     * Prove that the new <prev> -> <next> dependency would not
     * create a circular dependency in the graph. (We do this by
     * forward-recursing into the graph starting at <next>, and
     * checking whether we can reach <prev>.)
     *
     * We are using global variables to control the recursion, to
     * keep the stackframe size of the recursive functions low:
     */
    this.class = hlock_class(next);
    this.parent = NULL;
    ret = check_noncircular(&this, hlock_class(prev), &target_entry);
    if (unlikely(!ret))
        return print_circular_bug(&this, target_entry, next, prev);
    else if (unlikely(ret < 0))
        return print_bfs_bug(ret);

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

    /*
     * For recursive read-locks we do all the dependency checks,
     * but we dont store read-triggered dependencies (only
     * write-triggered dependencies). This ensures that only the
     * write-side dependencies matter, and that if for example a
     * write-lock never takes any other locks, then the reads are
     * equivalent to a NOP.
     */
    if (next->read == 2 || prev->read == 2)
        return 1;
    /*
     * Is the <prev> -> <next> dependency already present?
     *
     * (this may occur even though this is a new chain: consider
     *  e.g. the L1 -> L2 -> L3 -> L4 and the L5 -> L1 -> L2 -> L3
     *  chains - the second one will be new, but L1 already has
     *  L2 added to its dependency list, due to the first chain.)
     */
    list_for_each_entry(entry, &hlock_class(prev)->locks_after, entry) {
        if (entry->class == hlock_class(next)) {
            if (distance == 1)
                entry->distance = 1;
            return 2;
        }
    }

    if (!trylock_loop && !save_trace(&trace))
        return 0;

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

    if (!ret)
        return 0;

    ret = add_lock_to_list(hlock_class(next), hlock_class(prev),
                   &hlock_class(next)->locks_before,
                   next->acquire_ip, distance, &trace);
    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;
    int trylock_loop = 0;
    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, trylock_loop))
                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;
        trylock_loop = 1;
    }
    return 1;
out_bug:
    if (!debug_locks_off_graph_unlock())
        return 0;

    /*
     * Clearly we all shouldn't be here, but since we made it we
     * can reliable say we messed up our state. See the above two
     * gotos for reasons why we could possibly end up here.
     */
    WARN_ON(1);

    return 0;
}

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

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

/*
 * 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;

    /*
     * We might need to take the graph lock, ensure we've got IRQs
     * disabled to make this an IRQ-safe lock.. for recursion reasons
     * lockdep won't complain about its own locking errors.
     */
    if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
        return 0;
    /*
     * 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;
    if (likely(nr_chain_hlocks + chain->depth <= MAX_LOCKDEP_CHAIN_HLOCKS)) {
        chain->base = nr_chain_hlocks;
        nr_chain_hlocks += chain->depth;
        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();
            /*
             * We got mighty confused, our chain keys don't match
             * with what we expect, someone trample on our task state?
             */
            WARN(1, "hm#1, depth: %u [%u], %016Lx != %016Lx\n",
                curr->lockdep_depth, i,
                (unsigned long long)chain_key,
                (unsigned long long)hlock->prev_chain_key);
            return;
        }
        id = hlock->class_idx - 1;
        /*
         * Whoops ran out of static storage again?
         */
        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();
        /*
         * More smoking hash instead of calculating it, damn see these
         * numbers float.. I bet that a pink elephant stepped on my memory.
         */
        WARN(1, "hm#2, depth: %u [%u], %016Lx != %016Lx\n",
            curr->lockdep_depth, i,
            (unsigned long long)chain_key,
            (unsigned long long)curr->curr_chain_key);
    }
#endif
}

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

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

static int
print_usage_bug(struct task_struct *curr, struct held_lock *this,
        enum lock_usage_bit prev_bit, enum lock_usage_bit new_bit)
{
    if (!debug_locks_off_graph_unlock() || debug_locks_silent)
        return 0;

    printk("\n");
    printk("=================================\n");
    printk("[ INFO: inconsistent lock state ]\n");
    print_kernel_ident();
    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");
    print_usage_bug_scenario(this);

    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_list *root, struct lock_list *other,
            struct held_lock *this, int forwards,
            const char *irqclass)
{
    struct lock_list *entry = other;
    struct lock_list *middle = NULL;
    int depth;

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

    printk("\n");
    printk("=========================================================\n");
    printk("[ INFO: possible irq lock inversion dependency detected ]\n");
    print_kernel_ident();
    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->class);
    printk("\n\nand interrupts could create inverse lock ordering between them.\n\n");

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

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

    lockdep_print_held_locks(curr);

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

    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;
    struct lock_list root;
    struct lock_list *uninitialized_var(target_entry);

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

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

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

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

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

void print_irqtrace_events(struct task_struct *curr)
{
    printk("irq event stamp: %u\n", curr->irq_events);
    printk("hardirqs last  enabled at (%u): ", 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 (hlock_class(hlock)->key == __lockdep_no_validate__.subkeys)
            continue;

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

    return 1;
}

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

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

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

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

void trace_hardirqs_on_caller(unsigned long ip)
{
    time_hardirqs_on(CALLER_ADDR0, ip);

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

static 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;

    /*
     * Oi! Can't be having __GFP_FS allocations with IRQs disabled.
     */
    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 /* defined(CONFIG_TRACE_IRQFLAGS) && defined(CONFIG_PROVE_LOCKING) */

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

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

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

void lockdep_trace_alloc(gfp_t gfp_mask)
{
}

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

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

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

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

    hlock_class(this)->usage_mask |= new_mask;

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

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

    graph_unlock();

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

    return ret;
}

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

    kmemcheck_mark_initialized(lock, sizeof(*lock));

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

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

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

    lock->name = name;

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

    if (unlikely(!debug_locks))
        return;

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

struct lock_class_key __lockdep_no_validate__;

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

    printk("\n");
    printk("==================================\n");
    printk("[ BUG: Nested lock was not taken ]\n");
    print_kernel_ident();
    printk("----------------------------------\n");

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

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

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

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

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

    return 0;
}

static int __lock_is_held(struct lockdep_map *lock);

/*
 * 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,
              int references)
{
    struct task_struct *curr = current;
    struct lock_class *class = NULL;
    struct held_lock *hlock;
    unsigned int depth, id;
    int chain_head = 0;
    int class_idx;
    u64 chain_key;

    if (!prove_locking)
        check = 1;

    if (unlikely(!debug_locks))
        return 0;

    /*
     * Lockdep should run with IRQs disabled, otherwise we could
     * get an interrupt which would want to take locks, which would
     * end up in lockdep and have you got a head-ache already?
     */
    if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
        return 0;

    if (lock->key == &__lockdep_no_validate__)
        check = 1;

    if (subclass < NR_LOCKDEP_CACHING_CLASSES)
        class = lock->class_cache[subclass];
    /*
     * Not cached?
     */
    if (unlikely(!class)) {
        class = register_lock_class(lock, subclass, 0);
        if (!class)
            return 0;
    }
    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;
    /*
     * Ran out of static storage for our per-task lock stack again have we?
     */
    if (DEBUG_LOCKS_WARN_ON(depth >= MAX_LOCK_DEPTH))
        return 0;

    class_idx = class - lock_classes + 1;

    if (depth) {
        hlock = curr->held_locks + depth - 1;
        if (hlock->class_idx == class_idx && nest_lock) {
            if (hlock->references)
                hlock->references++;
            else
                hlock->references = 2;

            return 1;
        }
    }

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

    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;
    /*
     * Whoops, we did it again.. ran straight out of our static allocation.
     */
    if (DEBUG_LOCKS_WARN_ON(id >= MAX_LOCKDEP_KEYS))
        return 0;

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

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

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

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

    curr->curr_chain_key = chain_key;
    curr->lockdep_depth++;
    check_chain_key(curr);
#ifdef CONFIG_DEBUG_LOCKDEP
    if (unlikely(!debug_locks))
        return 0;
#endif
    if (unlikely(curr->lockdep_depth >= MAX_LOCK_DEPTH)) {
        debug_locks_off();
        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");
    printk("=====================================\n");
    printk("[ BUG: bad unlock balance detected! ]\n");
    print_kernel_ident();
    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;
    /*
     * Lockdep should run with IRQs disabled, recursion, head-ache, etc..
     */
    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 match_held_lock(struct held_lock *hlock, struct lockdep_map *lock)
{
    if (hlock->instance == lock)
        return 1;

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

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

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

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

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

    return 0;
}

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

    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 (match_held_lock(hlock, 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,
                hlock->references))
            return 0;
    }

    /*
     * I took it apart and put it back together again, except now I have
     * these 'spare' parts.. where shall I put them.
     */
    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;
    /*
     * So we're all set to release this lock.. wait what lock? We don't
     * own any locks, you've been drinking again?
     */
    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 (match_held_lock(hlock, lock))
            goto found_it;
        prev_hlock = hlock;
    }
    return print_unlock_inbalance_bug(curr, lock, ip);

found_it:
    if (hlock->instance == lock)
        lock_release_holdtime(hlock);

    if (hlock->references) {
        hlock->references--;
        if (hlock->references) {
            /*
             * We had, and after removing one, still have
             * references, the current lock stack is still
             * valid. We're done!
             */
            return 1;
        }
    }

    /*
     * 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,
                hlock->references))
            return 0;
    }

    /*
     * We had N bottles of beer on the wall, we drank one, but now
     * there's not N-1 bottles of beer left on the wall...
     */
    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 || hlock->references)
        return lock_release_non_nested(curr, lock, ip);
    curr->lockdep_depth--;

    /*
     * No more locks, but somehow we've got hash left over, who left it?
     */
    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);
}

static int __lock_is_held(struct lockdep_map *lock)
{
    struct task_struct *curr = current;
    int i;

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

        if (match_held_lock(hlock, lock))
            return 1;
    }

    return 0;
}

/*
 * 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()) {
            /* like the above, but with softirqs */
            DEBUG_LOCKS_WARN_ON(current->softirqs_enabled);
        } else {
            /* lick the above, does it taste good? */
            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);

/*
 * 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;

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

    raw_local_irq_save(flags);
    check_flags(flags);

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

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

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

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

int lock_is_held(struct lockdep_map *lock)
{
    unsigned long flags;
    int ret = 0;

    if (unlikely(current->lockdep_recursion))
        return 1; /* avoid false negative lockdep_assert_held() */

    raw_local_irq_save(flags);
    check_flags(flags);

    current->lockdep_recursion = 1;
    ret = __lock_is_held(lock);
    current->lockdep_recursion = 0;
    raw_local_irq_restore(flags);

    return ret;
}
EXPORT_SYMBOL_GPL(lock_is_held);

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");
    printk("=================================\n");
    printk("[ BUG: bad contention detected! ]\n");
    print_kernel_ident();
    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;
    /*
     * Whee, we contended on this lock, except it seems we're not
     * actually trying to acquire anything much at all..
     */
    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 (match_held_lock(hlock, lock))
            goto found_it;
        prev_hlock = hlock;
    }
    print_lock_contention_bug(curr, lock, ip);
    return;

found_it:
    if (hlock->instance != lock)
        return;

    hlock->waittime_stamp = lockstat_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, waittime = 0;
    int i, cpu;

    depth = curr->lockdep_depth;
    /*
     * Yay, we acquired ownership of this lock we didn't try to
     * acquire, how the heck did that happen?
     */
    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 (match_held_lock(hlock, lock))
            goto found_it;
        prev_hlock = hlock;
    }
    print_lock_contention_bug(curr, lock, _RET_IP_);
    return;

found_it:
    if (hlock->instance != lock)
        return;

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

    trace_lock_acquired(lock, ip);

    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;
}

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

    if (unlikely(!lock_stat))
        return;

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

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

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

    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) {
            int match = 0;

            for (j = 0; j < NR_LOCKDEP_CACHING_CLASSES; j++)
                match |= class == lock->class_cache[j];

            if (unlikely(match)) {
                if (debug_locks_off_graph_unlock()) {
                    /*
                     * We all just reset everything, how did it match?
                     */
                    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
#ifdef CONFIG_PROVE_LOCKING
        + sizeof(struct circular_queue)
#endif
        ) / 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! lock-%s was acquired"
            "before lockdep_init\n", lock_init_error);
        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");
    printk("=========================\n");
    printk("[ BUG: held lock freed! ]\n");
    print_kernel_ident();
    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");
    printk("=====================================\n");
    printk("[ BUG: lock held at task exit time! ]\n");
    print_kernel_ident();
    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 lockdep_sys_exit(void)
{
    struct task_struct *curr = current;

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

void lockdep_rcu_suspicious(const char *file, const int line, const char *s)
{
    struct task_struct *curr = current;

#ifndef CONFIG_PROVE_RCU_REPEATEDLY
    if (!debug_locks_off())
        return;
#endif /* #ifdef CONFIG_PROVE_RCU_REPEATEDLY */
    /* Note: the following can be executed concurrently, so be careful. */
    printk("\n");
    printk("===============================\n");
    printk("[ INFO: suspicious RCU usage. ]\n");
    print_kernel_ident();
    printk("-------------------------------\n");
    printk("%s:%d %s!\n", file, line, s);
    printk("\nother info that might help us debug this:\n\n");
    printk("\n%srcu_scheduler_active = %d, debug_locks = %d\n",
           !rcu_lockdep_current_cpu_online()
            ? "RCU used illegally from offline CPU!\n"
            : rcu_is_cpu_idle()
                ? "RCU used illegally from idle CPU!\n"
                : "",
           rcu_scheduler_active, debug_locks);

    /*
     * If a CPU is in the RCU-free window in idle (ie: in the section
     * between rcu_idle_enter() and rcu_idle_exit(), then RCU
     * considers that CPU to be in an "extended quiescent state",
     * which means that RCU will be completely ignoring that CPU.
     * Therefore, rcu_read_lock() and friends have absolutely no
     * effect on a CPU running in that state. In other words, even if
     * such an RCU-idle CPU has called rcu_read_lock(), RCU might well
     * delete data structures out from under it.  RCU really has no
     * choice here: we need to keep an RCU-free window in idle where
     * the CPU may possibly enter into low power mode. This way we can
     * notice an extended quiescent state to other CPUs that started a grace
     * period. Otherwise we would delay any grace period as long as we run
     * in the idle task.
     *
     * So complain bitterly if someone does call rcu_read_lock(),
     * rcu_read_lock_bh() and so on from extended quiescent states.
     */
    if (rcu_is_cpu_idle())
        printk("RCU used illegally from extended quiescent state!\n");

    lockdep_print_held_locks(curr);
    printk("\nstack backtrace:\n");
    dump_stack();
}
EXPORT_SYMBOL_GPL(lockdep_rcu_suspicious);