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lockdep.c

/*
 * kernel/lockdep.c
 *
 * Runtime locking correctness validator
 *
 * Started by Ingo Molnar:
 *
 *  Copyright (C) 2006,2007 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
 *  Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
 *
 * this code maps all the lock dependencies as they occur in a live kernel
 * and will warn about the following classes of locking bugs:
 *
 * - lock inversion scenarios
 * - circular lock dependencies
 * - hardirq/softirq safe/unsafe locking bugs
 *
 * Bugs are reported even if the current locking scenario does not cause
 * any deadlock at this point.
 *
 * I.e. if anytime in the past two locks were taken in a different order,
 * even if it happened for another task, even if those were different
 * locks (but of the same class as this lock), this code will detect it.
 *
 * Thanks to Arjan van de Ven for coming up with the initial idea of
 * mapping lock dependencies runtime.
 */
#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 <asm/sections.h>

#include "lockdep_internals.h"

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

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

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

static int graph_lock(void)
{
      __raw_spin_lock(&lockdep_lock);
      /*
       * Make sure that if another CPU detected a bug while
       * walking the graph we dont change it (while the other
       * CPU is busy printing out stuff with the graph lock
       * dropped already)
       */
      if (!debug_locks) {
            __raw_spin_unlock(&lockdep_lock);
            return 0;
      }
      return 1;
}

static inline int graph_unlock(void)
{
      if (debug_locks && !__raw_spin_is_locked(&lockdep_lock))
            return DEBUG_LOCKS_WARN_ON(1);

      __raw_spin_unlock(&lockdep_lock);
      return 0;
}

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

      __raw_spin_unlock(&lockdep_lock);

      return ret;
}

static int lockdep_initialized;

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

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

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

static int lock_contention_point(struct lock_class *class, unsigned long ip)
{
      int i;

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

      return i;
}

static void lock_time_inc(struct lock_time *lt, s64 time)
{
      if (time > lt->max)
            lt->max = time;

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

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

static inline void lock_time_add(struct lock_time *src, struct lock_time *dst)
{
      dst->min += src->min;
      dst->max += src->max;
      dst->total += src->total;
      dst->nr += src->nr;
}

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

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

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

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

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

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

      return stats;
}

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

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

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

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

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

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

      if (!lock_stat)
            return;

      holdtime = sched_clock() - hlock->holdtime_stamp;

      stats = get_lock_stats(hlock->class);
      if (hlock->read)
            lock_time_inc(&stats->read_holdtime, holdtime);
      else
            lock_time_inc(&stats->write_holdtime, holdtime);
      put_lock_stats(stats);
}
#else
static inline void lock_release_holdtime(struct held_lock *hlock)
{
}
#endif

/*
 * We keep a global list of all lock classes. The list only grows,
 * never shrinks. The list is only accessed with the lockdep
 * spinlock lock held.
 */
LIST_HEAD(all_lock_classes);

/*
 * The lockdep classes are in a hash-table as well, for fast lookup:
 */
#define CLASSHASH_BITS        (MAX_LOCKDEP_KEYS_BITS - 1)
#define CLASSHASH_SIZE        (1UL << CLASSHASH_BITS)
#define __classhashfn(key)    hash_long((unsigned long)key, CLASSHASH_BITS)
#define classhashentry(key)   (classhash_table + __classhashfn((key)))

static struct list_head classhash_table[CLASSHASH_SIZE];

/*
 * We put the lock dependency chains into a hash-table as well, to cache
 * their existence:
 */
#define CHAINHASH_BITS        (MAX_LOCKDEP_CHAINS_BITS-1)
#define CHAINHASH_SIZE        (1UL << CHAINHASH_BITS)
#define __chainhashfn(chain)  hash_long(chain, CHAINHASH_BITS)
#define chainhashentry(chain) (chainhash_table + __chainhashfn((chain)))

static struct list_head chainhash_table[CHAINHASH_SIZE];

/*
 * The hash key of the lock dependency chains is a hash itself too:
 * it's a hash of all locks taken up to that lock, including that lock.
 * It's a 64-bit hash, because it's important for the keys to be
 * unique.
 */
#define iterate_chain_key(key1, key2) \
      (((key1) << MAX_LOCKDEP_KEYS_BITS) ^ \
      ((key1) >> (64-MAX_LOCKDEP_KEYS_BITS)) ^ \
      (key2))

void lockdep_off(void)
{
      current->lockdep_recursion++;
}

EXPORT_SYMBOL(lockdep_off);

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

EXPORT_SYMBOL(lockdep_on);

/*
 * Debugging switches:
 */

#define VERBOSE               0
#define VERY_VERBOSE          0

#if VERBOSE
# define HARDIRQ_VERBOSE      1
# define SOFTIRQ_VERBOSE      1
#else
# define HARDIRQ_VERBOSE      0
# define SOFTIRQ_VERBOSE      0
#endif

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

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

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

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

      trace->skip = 3;

      save_stack_trace(trace);

      trace->max_entries = trace->nr_entries;

      nr_stack_trace_entries += trace->nr_entries;

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

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

            return 0;
      }

      return 1;
}

unsigned int nr_hardirq_chains;
unsigned int nr_softirq_chains;
unsigned int nr_process_chains;
unsigned int max_lockdep_depth;
unsigned int max_recursion_depth;

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

/*
 * Various lockdep statistics:
 */
atomic_t chain_lookup_hits;
atomic_t chain_lookup_misses;
atomic_t hardirqs_on_events;
atomic_t hardirqs_off_events;
atomic_t redundant_hardirqs_on;
atomic_t redundant_hardirqs_off;
atomic_t softirqs_on_events;
atomic_t softirqs_off_events;
atomic_t redundant_softirqs_on;
atomic_t redundant_softirqs_off;
atomic_t nr_unused_locks;
atomic_t nr_cyclic_checks;
atomic_t nr_cyclic_check_recursions;
atomic_t nr_find_usage_forwards_checks;
atomic_t nr_find_usage_forwards_recursions;
atomic_t nr_find_usage_backwards_checks;
atomic_t nr_find_usage_backwards_recursions;
# define debug_atomic_inc(ptr)            atomic_inc(ptr)
# define debug_atomic_dec(ptr)            atomic_dec(ptr)
# define debug_atomic_read(ptr)           atomic_read(ptr)
#else
# define debug_atomic_inc(ptr)            do { } while (0)
# define debug_atomic_dec(ptr)            do { } while (0)
# define debug_atomic_read(ptr)           0
#endif

/*
 * Locking printouts:
 */

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

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

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

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

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

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

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

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

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

      name = class->name;
      if (!name) {
            name = __get_key_name(class->key, str);
            printk(" (%s", name);
      } else {
            printk(" (%s", name);
            if (class->name_version > 1)
                  printk("#%d", class->name_version);
            if (class->subclass)
                  printk("/%d", class->subclass);
      }
      printk("){%c%c%c%c}", c1, c2, c3, c4);
}

static void print_lockdep_cache(struct lockdep_map *lock)
{
      const char *name;
      char str[KSYM_NAME_LEN];

      name = lock->name;
      if (!name)
            name = __get_key_name(lock->key->subkeys, str);

      printk("%s", name);
}

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

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

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

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

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

      printk("%*s->", depth, "");
      print_lock_name(class);
      printk(" ops: %lu", class->ops);
      printk(" {\n");

      for (bit = 0; bit < LOCK_USAGE_STATES; bit++) {
            if (class->usage_mask & (1 << bit)) {
                  int len = depth;

                  len += printk("%*s   %s", depth, "", usage_str[bit]);
                  len += printk(" at:\n");
                  print_stack_trace(class->usage_traces + bit, len);
            }
      }
      printk("%*s }\n", depth, "");

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

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

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

      print_lock_class_header(class, depth);

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

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

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

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

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

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

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

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

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

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

/*
 * To make lock name printouts unique, we calculate a unique
 * class->name_version generation counter:
 */
static int count_matching_names(struct lock_class *new_class)
{
      struct lock_class *class;
      int count = 0;

      if (!new_class->name)
            return 0;

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

      return count + 1;
}

/*
 * Register a lock's class in the hash-table, if the class is not present
 * yet. Otherwise we look it up. We cache the result in the lock object
 * itself, so actual lookup of the hash should be once per lock object.
 */
static inline struct lock_class *
look_up_lock_class(struct lockdep_map *lock, unsigned int subclass)
{
      struct lockdep_subclass_key *key;
      struct list_head *hash_head;
      struct lock_class *class;

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

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

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

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

      hash_head = classhashentry(key);

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

      return NULL;
}

/*
 * Register a lock's class in the hash-table, if the class is not present
 * yet. Otherwise we look it up. We cache the result in the lock object
 * itself, so actual lookup of the hash should be once per lock object.
 */
static inline struct lock_class *
register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force)
{
      struct lockdep_subclass_key *key;
      struct list_head *hash_head;
      struct lock_class *class;
      unsigned long flags;

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

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

            return NULL;
      }

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

      raw_local_irq_save(flags);
      if (!graph_lock()) {
            raw_local_irq_restore(flags);
            return NULL;
      }
      /*
       * We have to do the hash-walk again, to avoid races
       * with another CPU:
       */
      list_for_each_entry(class, hash_head, hash_entry)
            if (class->key == key)
                  goto out_unlock_set;
      /*
       * Allocate a new key from the static array, and add it to
       * the hash:
       */
      if (nr_lock_classes >= MAX_LOCKDEP_KEYS) {
            if (!debug_locks_off_graph_unlock()) {
                  raw_local_irq_restore(flags);
                  return NULL;
            }
            raw_local_irq_restore(flags);

            printk("BUG: MAX_LOCKDEP_KEYS too low!\n");
            printk("turning off the locking correctness validator.\n");
            return NULL;
      }
      class = lock_classes + nr_lock_classes++;
      debug_atomic_inc(&nr_unused_locks);
      class->key = key;
      class->name = lock->name;
      class->subclass = subclass;
      INIT_LIST_HEAD(&class->lock_entry);
      INIT_LIST_HEAD(&class->locks_before);
      INIT_LIST_HEAD(&class->locks_after);
      class->name_version = count_matching_names(class);
      /*
       * We use RCU's safe list-add method to make
       * parallel walking of the hash-list safe:
       */
      list_add_tail_rcu(&class->hash_entry, hash_head);

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

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

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

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

      if (DEBUG_LOCKS_WARN_ON(class->subclass != subclass))
            return NULL;

      return class;
}

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

            printk("BUG: MAX_LOCKDEP_ENTRIES too low!\n");
            printk("turning off the locking correctness validator.\n");
            return NULL;
      }
      return list_entries + nr_list_entries++;
}

/*
 * Add a new dependency to the head of the list:
 */
static int add_lock_to_list(struct lock_class *class, struct lock_class *this,
                      struct list_head *head, unsigned long ip, int distance)
{
      struct lock_list *entry;
      /*
       * Lock not present yet - get a new dependency struct and
       * add it to the list:
       */
      entry = alloc_list_entry();
      if (!entry)
            return 0;

      entry->class = this;
      entry->distance = distance;
      if (!save_trace(&entry->trace))
            return 0;

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

      return 1;
}

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

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

      return 0;
}

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

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

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

      print_circular_bug_entry(entry, depth);

      return 0;
}

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

      if (debug_locks_silent)
            return 0;

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

      print_circular_bug_entry(&this, 0);

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

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

      return 0;
}

#define RECURSION_LIMIT 40

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

      WARN_ON(1);

      return 0;
}

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

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

#ifdef CONFIG_TRACE_IRQFLAGS
/*
 * Forwards and backwards subgraph searching, for the purposes of
 * proving that two subgraphs can be connected by a new dependency
 * without creating any illegal irq-safe -> irq-unsafe lock dependency.
 */
static enum lock_usage_bit find_usage_bit;
static struct lock_class *forwards_match, *backwards_match;

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

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

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

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

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

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

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

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

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

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

      printk("\n======================================================\n");
      printk(  "[ INFO: %s-safe -> %s-unsafe lock order detected ]\n",
            irqclass, irqclass);
      print_kernel_version();
      printk(  "------------------------------------------------------\n");
      printk("%s/%d [HC%u[%lu]:SC%u[%lu]:HE%u:SE%u] is trying to acquire:\n",
            curr->comm, task_pid_nr(curr),
            curr->hardirq_context, hardirq_count() >> HARDIRQ_SHIFT,
            curr->softirq_context, softirq_count() >> SOFTIRQ_SHIFT,
            curr->hardirqs_enabled,
            curr->softirqs_enabled);
      print_lock(next);

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

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

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

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

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

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

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

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

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

      return 0;
}

static int
check_usage(struct task_struct *curr, struct held_lock *prev,
          struct held_lock *next, enum lock_usage_bit bit_backwards,
          enum lock_usage_bit bit_forwards, const char *irqclass)
{
      int ret;

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

      find_usage_bit = bit_forwards;
      ret = find_usage_forwards(next->class, 0);
      if (!ret || ret == 1)
            return ret;
      /* ret == 2 */
      return print_bad_irq_dependency(curr, prev, next,
                  bit_backwards, bit_forwards, irqclass);
}

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

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

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

      return 1;
}

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

#else

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

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

#endif

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

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

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

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

      return 0;
}

/*
 * Check whether we are holding such a class already.
 *
 * (Note that this has to be done separately, because the graph cannot
 * detect such classes of deadlocks.)
 *
 * Returns: 0 on deadlock detected, 1 on OK, 2 on recursive read
 */
static int
check_deadlock(struct task_struct *curr, struct held_lock *next,
             struct lockdep_map *next_instance, int read)
{
      struct held_lock *prev;
      int i;

      for (i = 0; i < curr->lockdep_depth; i++) {
            prev = curr->held_locks + i;
            if (prev->class != next->class)
                  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;
            return print_deadlock_bug(curr, prev, next);
      }
      return 1;
}

/*
 * There was a chain-cache miss, and we are about to add a new dependency
 * to a previous lock. We recursively validate the following rules:
 *
 *  - would the adding of the <prev> -> <next> dependency create a
 *    circular dependency in the graph? [== circular deadlock]
 *
 *  - does the new prev->next dependency connect any hardirq-safe lock
 *    (in the full backwards-subgraph starting at <prev>) with any
 *    hardirq-unsafe lock (in the full forwards-subgraph starting at
 *    <next>)? [== illegal lock inversion with hardirq contexts]
 *
 *  - does the new prev->next dependency connect any softirq-safe lock
 *    (in the full backwards-subgraph starting at <prev>) with any
 *    softirq-unsafe lock (in the full forwards-subgraph starting at
 *    <next>)? [== illegal lock inversion with softirq contexts]
 *
 * any of these scenarios could lead to a deadlock.
 *
 * Then if all the validations pass, we add the forwards and backwards
 * dependency.
 */
static int
check_prev_add(struct task_struct *curr, struct held_lock *prev,
             struct held_lock *next, int distance)
{
      struct lock_list *entry;
      int ret;

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

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

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

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

      if (!ret)
            return 0;

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

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

/*
 * Add the dependency to all directly-previous locks that are 'relevant'.
 * The ones that are relevant are (in increasing distance from curr):
 * all consecutive trylock entries and the final non-trylock entry - or
 * the end of this context's lock-chain - whichever comes first.
 */
static int
check_prevs_add(struct task_struct *curr, struct held_lock *next)
{
      int depth = curr->lockdep_depth;
      struct held_lock *hlock;

      /*
       * Debugging checks.
       *
       * Depth must not be zero for a non-head lock:
       */
      if (!depth)
            goto out_bug;
      /*
       * At least two relevant locks must exist for this
       * to be a head:
       */
      if (curr->held_locks[depth].irq_context !=
                  curr->held_locks[depth-1].irq_context)
            goto out_bug;

      for (;;) {
            int distance = curr->lockdep_depth - depth + 1;
            hlock = curr->held_locks + depth-1;
            /*
             * Only non-recursive-read entries get new dependencies
             * added:
             */
            if (hlock->read != 2) {
                  if (!check_prev_add(curr, hlock, next, distance))
                        return 0;
                  /*
                   * Stop after the first non-trylock entry,
                   * as non-trylock entries have added their
                   * own direct dependencies already, so this
                   * lock is connected to them indirectly:
                   */
                  if (!hlock->trylock)
                        break;
            }
            depth--;
            /*
             * End of lock-stack?
             */
            if (!depth)
                  break;
            /*
             * Stop the search if we cross into another context:
             */
            if (curr->held_locks[depth].irq_context !=
                        curr->held_locks[depth-1].irq_context)
                  break;
      }
      return 1;
out_bug:
      if (!debug_locks_off_graph_unlock())
            return 0;

      WARN_ON(1);

      return 0;
}

unsigned long nr_lock_chains;
static struct lock_chain lock_chains[MAX_LOCKDEP_CHAINS];

/*
 * 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(u64 chain_key, struct lock_class *class)
{
      struct list_head *hash_head = chainhashentry(chain_key);
      struct lock_chain *chain;

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

            printk("BUG: MAX_LOCKDEP_CHAINS too low!\n");
            printk("turning off the locking correctness validator.\n");
            return 0;
      }
      chain = lock_chains + nr_lock_chains++;
      chain->chain_key = chain_key;
      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(chain_key, hlock->class)) {
            /*
             * 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();
                  printk("hm#1, depth: %u [%u], %016Lx != %016Lx\n",
                        curr->lockdep_depth, i,
                        (unsigned long long)chain_key,
                        (unsigned long long)hlock->prev_chain_key);
                  WARN_ON(1);
                  return;
            }
            id = hlock->class - lock_classes;
            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();
            printk("hm#2, depth: %u [%u], %016Lx != %016Lx\n",
                  curr->lockdep_depth, i,
                  (unsigned long long)chain_key,
                  (unsigned long long)curr->curr_chain_key);
            WARN_ON(1);
      }
#endif
}

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

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

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

      printk("%s/%d [HC%u[%lu]:SC%u[%lu]:HE%u:SE%u] takes:\n",
            curr->comm, task_pid_nr(curr),
            trace_hardirq_context(curr), hardirq_count() >> HARDIRQ_SHIFT,
            trace_softirq_context(curr), softirq_count() >> SOFTIRQ_SHIFT,
            trace_hardirqs_enabled(curr),
            trace_softirqs_enabled(curr));
      print_lock(this);

      printk("{%s} state was registered at:\n", usage_str[prev_bit]);
      print_stack_trace(this->class->usage_traces + prev_bit, 1);

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

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

      return 0;
}

/*
 * Print out an error if an invalid bit is set:
 */
static inline int
valid_state(struct task_struct *curr, struct held_lock *this,
          enum lock_usage_bit new_bit, enum lock_usage_bit bad_bit)
{
      if (unlikely(this->class->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);

#ifdef CONFIG_TRACE_IRQFLAGS

/*
 * print irq inversion bug:
 */
static int
print_irq_inversion_bug(struct task_struct *curr, struct lock_class *other,
                  struct held_lock *this, int forwards,
                  const char *irqclass)
{
      if (!debug_locks_off_graph_unlock() || debug_locks_silent)
            return 0;

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

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

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

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

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

      return 0;
}

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

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

      return print_irq_inversion_bug(curr, forwards_match, this, 1, irqclass);
}

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

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

      return print_irq_inversion_bug(curr, backwards_match, this, 0, irqclass);
}

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

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

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

#define STRICT_READ_CHECKS    1

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

      switch(new_bit) {
      case LOCK_USED_IN_HARDIRQ:
            if (!valid_state(curr, this, new_bit, LOCK_ENABLED_HARDIRQS))
                  return 0;
            if (!valid_state(curr, this, new_bit,
                         LOCK_ENABLED_HARDIRQS_READ))
                  return 0;
            /*
             * just marked it hardirq-safe, check that this lock
             * took no hardirq-unsafe lock in the past:
             */
            if (!check_usage_forwards(curr, this,
                                LOCK_ENABLED_HARDIRQS, "hard"))
                  return 0;
#if STRICT_READ_CHECKS
            /*
             * just marked it hardirq-safe, check that this lock
             * took no hardirq-unsafe-read lock in the past:
             */
            if (!check_usage_forwards(curr, this,
                        LOCK_ENABLED_HARDIRQS_READ, "hard-read"))
                  return 0;
#endif
            if (hardirq_verbose(this->class))
                  ret = 2;
            break;
      case LOCK_USED_IN_SOFTIRQ:
            if (!valid_state(curr, this, new_bit, LOCK_ENABLED_SOFTIRQS))
                  return 0;
            if (!valid_state(curr, this, new_bit,
                         LOCK_ENABLED_SOFTIRQS_READ))
                  return 0;
            /*
             * just marked it softirq-safe, check that this lock
             * took no softirq-unsafe lock in the past:
             */
            if (!check_usage_forwards(curr, this,
                                LOCK_ENABLED_SOFTIRQS, "soft"))
                  return 0;
#if STRICT_READ_CHECKS
            /*
             * just marked it softirq-safe, check that this lock
             * took no softirq-unsafe-read lock in the past:
             */
            if (!check_usage_forwards(curr, this,
                        LOCK_ENABLED_SOFTIRQS_READ, "soft-read"))
                  return 0;
#endif
            if (softirq_verbose(this->class))
                  ret = 2;
            break;
      case LOCK_USED_IN_HARDIRQ_READ:
            if (!valid_state(curr, this, new_bit, LOCK_ENABLED_HARDIRQS))
                  return 0;
            /*
             * just marked it hardirq-read-safe, check that this lock
             * took no hardirq-unsafe lock in the past:
             */
            if (!check_usage_forwards(curr, this,
                                LOCK_ENABLED_HARDIRQS, "hard"))
                  return 0;
            if (hardirq_verbose(this->class))
                  ret = 2;
            break;
      case LOCK_USED_IN_SOFTIRQ_READ:
            if (!valid_state(curr, this, new_bit, LOCK_ENABLED_SOFTIRQS))
                  return 0;
            /*
             * just marked it softirq-read-safe, check that this lock
             * took no softirq-unsafe lock in the past:
             */
            if (!check_usage_forwards(curr, this,
                                LOCK_ENABLED_SOFTIRQS, "soft"))
                  return 0;
            if (softirq_verbose(this->class))
                  ret = 2;
            break;
      case LOCK_ENABLED_HARDIRQS:
            if (!valid_state(curr, this, new_bit, LOCK_USED_IN_HARDIRQ))
                  return 0;
            if (!valid_state(curr, this, new_bit,
                         LOCK_USED_IN_HARDIRQ_READ))
                  return 0;
            /*
             * just marked it hardirq-unsafe, check that no hardirq-safe
             * lock in the system ever took it in the past:
             */
            if (!check_usage_backwards(curr, this,
                                 LOCK_USED_IN_HARDIRQ, "hard"))
                  return 0;
#if STRICT_READ_CHECKS
            /*
             * just marked it hardirq-unsafe, check that no
             * hardirq-safe-read lock in the system ever took
             * it in the past:
             */
            if (!check_usage_backwards(curr, this,
                           LOCK_USED_IN_HARDIRQ_READ, "hard-read"))
                  return 0;
#endif
            if (hardirq_verbose(this->class))
                  ret = 2;
            break;
      case LOCK_ENABLED_SOFTIRQS:
            if (!valid_state(curr, this, new_bit, LOCK_USED_IN_SOFTIRQ))
                  return 0;
            if (!valid_state(curr, this, new_bit,
                         LOCK_USED_IN_SOFTIRQ_READ))
                  return 0;
            /*
             * just marked it softirq-unsafe, check that no softirq-safe
             * lock in the system ever took it in the past:
             */
            if (!check_usage_backwards(curr, this,
                                 LOCK_USED_IN_SOFTIRQ, "soft"))
                  return 0;
#if STRICT_READ_CHECKS
            /*
             * just marked it softirq-unsafe, check that no
             * softirq-safe-read lock in the system ever took
             * it in the past:
             */
            if (!check_usage_backwards(curr, this,
                           LOCK_USED_IN_SOFTIRQ_READ, "soft-read"))
                  return 0;
#endif
            if (softirq_verbose(this->class))
                  ret = 2;
            break;
      case LOCK_ENABLED_HARDIRQS_READ:
            if (!valid_state(curr, this, new_bit, LOCK_USED_IN_HARDIRQ))
                  return 0;
#if STRICT_READ_CHECKS
            /*
             * just marked it hardirq-read-unsafe, check that no
             * hardirq-safe lock in the system ever took it in the past:
             */
            if (!check_usage_backwards(curr, this,
                                 LOCK_USED_IN_HARDIRQ, "hard"))
                  return 0;
#endif
            if (hardirq_verbose(this->class))
                  ret = 2;
            break;
      case LOCK_ENABLED_SOFTIRQS_READ:
            if (!valid_state(curr, this, new_bit, LOCK_USED_IN_SOFTIRQ))
                  return 0;
#if STRICT_READ_CHECKS
            /*
             * just marked it softirq-read-unsafe, check that no
             * softirq-safe lock in the system ever took it in the past:
             */
            if (!check_usage_backwards(curr, this,
                                 LOCK_USED_IN_SOFTIRQ, "soft"))
                  return 0;
#endif
            if (softirq_verbose(this->class))
                  ret = 2;
            break;
      default:
            WARN_ON(1);
            break;
      }

      return ret;
}

/*
 * Mark all held locks with a usage bit:
 */
static int
mark_held_locks(struct task_struct *curr, int hardirq)
{
      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;

            if (hardirq) {
                  if (hlock->read)
                        usage_bit = LOCK_ENABLED_HARDIRQS_READ;
                  else
                        usage_bit = LOCK_ENABLED_HARDIRQS;
            } else {
                  if (hlock->read)
                        usage_bit = LOCK_ENABLED_SOFTIRQS_READ;
                  else
                        usage_bit = LOCK_ENABLED_SOFTIRQS;
            }
            if (!mark_lock(curr, hlock, usage_bit))
                  return 0;
      }

      return 1;
}

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

void early_boot_irqs_off(void)
{
      early_boot_irqs_enabled = 0;
}

void early_boot_irqs_on(void)
{
      early_boot_irqs_enabled = 1;
}

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

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

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

      if (unlikely(curr->hardirqs_enabled)) {
            debug_atomic_inc(&redundant_hardirqs_on);
            return;
      }
      /* we'll do an OFF -> ON transition: */
      curr->hardirqs_enabled = 1;
      ip = (unsigned long) __builtin_return_address(0);

      if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
            return;
      if (DEBUG_LOCKS_WARN_ON(current->hardirq_context))
            return;
      /*
       * We are going to turn hardirqs on, so set the
       * usage bit for all held locks:
       */
      if (!mark_held_locks(curr, 1))
            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, 0))
                  return;

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

EXPORT_SYMBOL(trace_hardirqs_on);

/*
 * Hardirqs were disabled:
 */
void trace_hardirqs_off(void)
{
      struct task_struct *curr = current;

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

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

      if (curr->hardirqs_enabled) {
            /*
             * We have done an ON -> OFF transition:
             */
            curr->hardirqs_enabled = 0;
            curr->hardirq_disable_ip = _RET_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);

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

      if (unlikely(!debug_locks))
            return;

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

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

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

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

      if (unlikely(!debug_locks))
            return;

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

      if (curr->softirqs_enabled) {
            /*
             * We have done an ON -> OFF transition:
             */
            curr->softirqs_enabled = 0;
            curr->softirq_disable_ip = ip;
            curr->softirq_disable_event = ++curr->irq_events;
            debug_atomic_inc(&softirqs_off_events);
            DEBUG_LOCKS_WARN_ON(!softirq_count());
      } else
            debug_atomic_inc(&redundant_softirqs_off);
}

static 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_HARDIRQS_READ))
                        return 0;
                  if (curr->softirqs_enabled)
                        if (!mark_lock(curr, hlock,
                                    LOCK_ENABLED_SOFTIRQS_READ))
                              return 0;
            } else {
                  if (!mark_lock(curr, hlock,
                              LOCK_ENABLED_HARDIRQS))
                        return 0;
                  if (curr->softirqs_enabled)
                        if (!mark_lock(curr, hlock,
                                    LOCK_ENABLED_SOFTIRQS))
                              return 0;
            }
      }

      return 1;
}

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

      /*
       * Keep track of points where we cross into an interrupt context:
       */
      hlock->irq_context = 2*(curr->hardirq_context ? 1 : 0) +
                        curr->softirq_context;
      if (depth) {
            struct held_lock *prev_hlock;

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

#else

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

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

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

#endif

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

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

      if (!graph_lock())
            return 0;
      /*
       * Make sure we didnt race:
       */
      if (unlikely(this->class->usage_mask & new_mask)) {
            graph_unlock();
            return 1;
      }

      this->class->usage_mask |= new_mask;

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

      switch (new_bit) {
      case LOCK_USED_IN_HARDIRQ:
      case LOCK_USED_IN_SOFTIRQ:
      case LOCK_USED_IN_HARDIRQ_READ:
      case LOCK_USED_IN_SOFTIRQ_READ:
      case LOCK_ENABLED_HARDIRQS:
      case LOCK_ENABLED_SOFTIRQS:
      case LOCK_ENABLED_HARDIRQS_READ:
      case LOCK_ENABLED_SOFTIRQS_READ:
            ret = mark_lock_irq(curr, this, new_bit);
            if (!ret)
                  return 0;
            break;
      case LOCK_USED:
            /*
             * Add it to the global list of classes:
             */
            list_add_tail_rcu(&this->class->lock_entry, &all_lock_classes);
            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)
{
      if (unlikely(!debug_locks))
            return;

      if (DEBUG_LOCKS_WARN_ON(!key))
            return;
      if (DEBUG_LOCKS_WARN_ON(!name))
            return;
      /*
       * Sanity check, the lock-class key must be persistent:
       */
      if (!static_obj(key)) {
            printk("BUG: key %p not in .data!\n", key);
            DEBUG_LOCKS_WARN_ON(1);
            return;
      }
      lock->name = name;
      lock->key = key;
      lock->class_cache = NULL;
#ifdef CONFIG_LOCK_STAT
      lock->cpu = raw_smp_processor_id();
#endif
      if (subclass)
            register_lock_class(lock, subclass, 1);
}

EXPORT_SYMBOL_GPL(lockdep_init_map);

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

      if (!prove_locking)
            check = 1;

      if (unlikely(!debug_locks))
            return 0;

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

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

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

      /*
       * Add the lock to the list of currently held locks.
       * (we dont increase the depth just yet, up until the
       * dependency checks are done)
       */
      depth = curr->lockdep_depth;
      if (DEBUG_LOCKS_WARN_ON(depth >= MAX_LOCK_DEPTH))
            return 0;

      hlock = curr->held_locks + depth;

      hlock->class = class;
      hlock->acquire_ip = ip;
      hlock->instance = lock;
      hlock->trylock = trylock;
      hlock->read = read;
      hlock->check = check;
      hlock->hardirqs_off = hardirqs_off;
#ifdef CONFIG_LOCK_STAT
      hlock->waittime_stamp = 0;
      hlock->holdtime_stamp = sched_clock();
#endif

      if (check == 2 && !mark_irqflags(curr, hlock))
            return 0;

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

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

      chain_key = curr->curr_chain_key;
      if (!depth) {
            if (DEBUG_LOCKS_WARN_ON(chain_key != 0))
                  return 0;
            chain_head = 1;
      }

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

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

      curr->curr_chain_key = chain_key;
      curr->lockdep_depth++;
      check_chain_key(curr);
#ifdef CONFIG_DEBUG_LOCKDEP
      if (unlikely(!debug_locks))
            return 0;
#endif
      if (unlikely(curr->lockdep_depth >= MAX_LOCK_DEPTH)) {
            debug_locks_off();
            printk("BUG: MAX_LOCK_DEPTH too low!\n");
            printk("turning off the locking correctness validator.\n");
            return 0;
      }

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

      return 1;
}

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

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

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

      return 0;
}

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

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

      return 1;
}

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

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

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

found_it:
      lock_release_holdtime(hlock);

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

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

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

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

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

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

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

      curr->curr_chain_key = hlock->prev_chain_key;

      lock_release_holdtime(hlock);

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

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

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

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

      check_chain_key(curr);
}

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

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

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

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

/*
 * 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, unsigned long ip)
{
      unsigned long flags;

      if (unlikely(!lock_stat && !prove_locking))
            return;

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

      raw_local_irq_save(flags);
      check_flags(flags);

      current->lockdep_recursion = 1;
      __lock_acquire(lock, subclass, trylock, read, check,
                   irqs_disabled_flags(flags), ip);
      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(!lock_stat && !prove_locking))
            return;

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

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

EXPORT_SYMBOL_GPL(lock_release);

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

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

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

      return 0;
}

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

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

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

found_it:
      hlock->waittime_stamp = sched_clock();

      point = lock_contention_point(hlock->class, ip);

      stats = get_lock_stats(hlock->class);
      if (point < ARRAY_SIZE(stats->contention_point))
            stats->contention_point[i]++;
      if (lock->cpu != smp_processor_id())
            stats->bounces[bounce_contended + !!hlock->read]++;
      put_lock_stats(stats);
}

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

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

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

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

      stats = get_lock_stats(hlock->class);
      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;
}

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;
      __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 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);
      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);

}

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

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

      raw_local_irq_save(flags);
      locked = graph_lock();

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

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

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

      raw_local_irq_save(flags);

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

out_restore:
      raw_local_irq_restore(flags);
}

void lockdep_init(void)
{
      int i;

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

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

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

      lockdep_initialized = 1;
}

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

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

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

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

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

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

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

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

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

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

      if (unlikely(!debug_locks))
            return;

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

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

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

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

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

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

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

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

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

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

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

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