FreeBSD/Linux Kernel Cross Reference
sys/kernel/lockdep.c

     /*
      * kernel/lockdep.c
      *
      * Runtime locking correctness validator
      *
      * Started by Ingo Molnar:
      *
      *  Copyright (C) 2006,2007 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
      *  Copyright (C) 2007 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
     *
     * this code maps all the lock dependencies as they occur in a live kernel
     * and will warn about the following classes of locking bugs:
     *
     * - lock inversion scenarios
     * - circular lock dependencies
     * - hardirq/softirq safe/unsafe locking bugs
     *
     * Bugs are reported even if the current locking scenario does not cause
     * any deadlock at this point.
     *
     * I.e. if anytime in the past two locks were taken in a different order,
     * even if it happened for another task, even if those were different
     * locks (but of the same class as this lock), this code will detect it.
     *
     * Thanks to Arjan van de Ven for coming up with the initial idea of
     * mapping lock dependencies runtime.
     */
    #define DISABLE_BRANCH_PROFILING
    #include <linux/mutex.h>
    #include <linux/sched.h>
    #include <linux/delay.h>
    #include <linux/module.h>
    #include <linux/proc_fs.h>
    #include <linux/seq_file.h>
    #include <linux/spinlock.h>
    #include <linux/kallsyms.h>
    #include <linux/interrupt.h>
    #include <linux/stacktrace.h>
    #include <linux/debug_locks.h>
    #include <linux/irqflags.h>
    #include <linux/utsname.h>
    #include <linux/hash.h>
    #include <linux/ftrace.h>
    #include <linux/stringify.h>
    #include <linux/bitops.h>
    #include <linux/gfp.h>
    #include <linux/kmemcheck.h>
    
    #include <asm/sections.h>
    
    #include "lockdep_internals.h"
    
    #define CREATE_TRACE_POINTS
    #include <trace/events/lock.h>
    
    #ifdef CONFIG_PROVE_LOCKING
    int prove_locking = 1;
    module_param(prove_locking, int, 0644);
    #else
    #define prove_locking 0
    #endif
    
    #ifdef CONFIG_LOCK_STAT
    int lock_stat = 1;
    module_param(lock_stat, int, 0644);
    #else
    #define lock_stat 0
    #endif
    
    /*
     * lockdep_lock: protects the lockdep graph, the hashes and the
     *               class/list/hash allocators.
     *
     * This is one of the rare exceptions where it's justified
     * to use a raw spinlock - we really dont want the spinlock
     * code to recurse back into the lockdep code...
     */
    static arch_spinlock_t lockdep_lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
    
    static int graph_lock(void)
    {
            arch_spin_lock(&lockdep_lock);
            /*
             * Make sure that if another CPU detected a bug while
             * walking the graph we dont change it (while the other
             * CPU is busy printing out stuff with the graph lock
             * dropped already)
             */
            if (!debug_locks) {
                    arch_spin_unlock(&lockdep_lock);
                    return 0;
            }
            /* prevent any recursions within lockdep from causing deadlocks */
            current->lockdep_recursion++;
            return 1;
    }
    
    static inline int graph_unlock(void)
    {
           if (debug_locks && !arch_spin_is_locked(&lockdep_lock)) {
                   /*
                    * The lockdep graph lock isn't locked while we expect it to
                    * be, we're confused now, bye!
                    */
                   return DEBUG_LOCKS_WARN_ON(1);
           }
   
           current->lockdep_recursion--;
           arch_spin_unlock(&lockdep_lock);
           return 0;
   }
   
   /*
    * Turn lock debugging off and return with 0 if it was off already,
    * and also release the graph lock:
    */
   static inline int debug_locks_off_graph_unlock(void)
   {
           int ret = debug_locks_off();
   
           arch_spin_unlock(&lockdep_lock);
   
           return ret;
   }
   
   static int lockdep_initialized;
   
   unsigned long nr_list_entries;
   static struct lock_list list_entries[MAX_LOCKDEP_ENTRIES];
   
   /*
    * All data structures here are protected by the global debug_lock.
    *
    * Mutex key structs only get allocated, once during bootup, and never
    * get freed - this significantly simplifies the debugging code.
    */
   unsigned long nr_lock_classes;
   static struct lock_class lock_classes[MAX_LOCKDEP_KEYS];
   
   static inline struct lock_class *hlock_class(struct held_lock *hlock)
   {
           if (!hlock->class_idx) {
                   /*
                    * Someone passed in garbage, we give up.
                    */
                   DEBUG_LOCKS_WARN_ON(1);
                   return NULL;
           }
           return lock_classes + hlock->class_idx - 1;
   }
   
   #ifdef CONFIG_LOCK_STAT
   static DEFINE_PER_CPU(struct lock_class_stats[MAX_LOCKDEP_KEYS],
                         cpu_lock_stats);
   
   static inline u64 lockstat_clock(void)
   {
           return local_clock();
   }
   
   static int lock_point(unsigned long points[], unsigned long ip)
   {
           int i;
   
           for (i = 0; i < LOCKSTAT_POINTS; i++) {
                   if (points[i] == 0) {
                           points[i] = ip;
                           break;
                   }
                   if (points[i] == ip)
                           break;
           }
   
           return i;
   }
   
   static void lock_time_inc(struct lock_time *lt, u64 time)
   {
           if (time > lt->max)
                   lt->max = time;
   
           if (time < lt->min || !lt->nr)
                   lt->min = time;
   
           lt->total += time;
           lt->nr++;
   }
   
   static inline void lock_time_add(struct lock_time *src, struct lock_time *dst)
   {
           if (!src->nr)
                   return;
   
           if (src->max > dst->max)
                   dst->max = src->max;
   
           if (src->min < dst->min || !dst->nr)
                   dst->min = src->min;
   
           dst->total += src->total;
           dst->nr += src->nr;
   }
   
   struct lock_class_stats lock_stats(struct lock_class *class)
   {
           struct lock_class_stats stats;
           int cpu, i;
   
           memset(&stats, 0, sizeof(struct lock_class_stats));
           for_each_possible_cpu(cpu) {
                   struct lock_class_stats *pcs =
                           &per_cpu(cpu_lock_stats, cpu)[class - lock_classes];
   
                   for (i = 0; i < ARRAY_SIZE(stats.contention_point); i++)
                           stats.contention_point[i] += pcs->contention_point[i];
   
                   for (i = 0; i < ARRAY_SIZE(stats.contending_point); i++)
                           stats.contending_point[i] += pcs->contending_point[i];
   
                   lock_time_add(&pcs->read_waittime, &stats.read_waittime);
                   lock_time_add(&pcs->write_waittime, &stats.write_waittime);
   
                   lock_time_add(&pcs->read_holdtime, &stats.read_holdtime);
                   lock_time_add(&pcs->write_holdtime, &stats.write_holdtime);
   
                   for (i = 0; i < ARRAY_SIZE(stats.bounces); i++)
                           stats.bounces[i] += pcs->bounces[i];
           }
   
           return stats;
   }
   
   void clear_lock_stats(struct lock_class *class)
   {
           int cpu;
   
           for_each_possible_cpu(cpu) {
                   struct lock_class_stats *cpu_stats =
                           &per_cpu(cpu_lock_stats, cpu)[class - lock_classes];
   
                   memset(cpu_stats, 0, sizeof(struct lock_class_stats));
           }
           memset(class->contention_point, 0, sizeof(class->contention_point));
           memset(class->contending_point, 0, sizeof(class->contending_point));
   }
   
   static struct lock_class_stats *get_lock_stats(struct lock_class *class)
   {
           return &get_cpu_var(cpu_lock_stats)[class - lock_classes];
   }
   
   static void put_lock_stats(struct lock_class_stats *stats)
   {
           put_cpu_var(cpu_lock_stats);
   }
   
   static void lock_release_holdtime(struct held_lock *hlock)
   {
           struct lock_class_stats *stats;
           u64 holdtime;
   
           if (!lock_stat)
                   return;
   
           holdtime = lockstat_clock() - hlock->holdtime_stamp;
   
           stats = get_lock_stats(hlock_class(hlock));
           if (hlock->read)
                   lock_time_inc(&stats->read_holdtime, holdtime);
           else
                   lock_time_inc(&stats->write_holdtime, holdtime);
           put_lock_stats(stats);
   }
   #else
   static inline void lock_release_holdtime(struct held_lock *hlock)
   {
   }
   #endif
   
   /*
    * We keep a global list of all lock classes. The list only grows,
    * never shrinks. The list is only accessed with the lockdep
    * spinlock lock held.
    */
   LIST_HEAD(all_lock_classes);
   
   /*
    * The lockdep classes are in a hash-table as well, for fast lookup:
    */
   #define CLASSHASH_BITS          (MAX_LOCKDEP_KEYS_BITS - 1)
   #define CLASSHASH_SIZE          (1UL << CLASSHASH_BITS)
   #define __classhashfn(key)      hash_long((unsigned long)key, CLASSHASH_BITS)
   #define classhashentry(key)     (classhash_table + __classhashfn((key)))
   
   static struct list_head classhash_table[CLASSHASH_SIZE];
   
   /*
    * We put the lock dependency chains into a hash-table as well, to cache
    * their existence:
    */
   #define CHAINHASH_BITS          (MAX_LOCKDEP_CHAINS_BITS-1)
   #define CHAINHASH_SIZE          (1UL << CHAINHASH_BITS)
   #define __chainhashfn(chain)    hash_long(chain, CHAINHASH_BITS)
   #define chainhashentry(chain)   (chainhash_table + __chainhashfn((chain)))
   
   static struct list_head chainhash_table[CHAINHASH_SIZE];
   
   /*
    * The hash key of the lock dependency chains is a hash itself too:
    * it's a hash of all locks taken up to that lock, including that lock.
    * It's a 64-bit hash, because it's important for the keys to be
    * unique.
    */
   #define iterate_chain_key(key1, key2) \
           (((key1) << MAX_LOCKDEP_KEYS_BITS) ^ \
           ((key1) >> (64-MAX_LOCKDEP_KEYS_BITS)) ^ \
           (key2))
   
   void lockdep_off(void)
   {
           current->lockdep_recursion++;
   }
   EXPORT_SYMBOL(lockdep_off);
   
   void lockdep_on(void)
   {
           current->lockdep_recursion--;
   }
   EXPORT_SYMBOL(lockdep_on);
   
   /*
    * Debugging switches:
    */
   
   #define VERBOSE                 0
   #define VERY_VERBOSE            0
   
   #if VERBOSE
   # define HARDIRQ_VERBOSE        1
   # define SOFTIRQ_VERBOSE        1
   # define RECLAIM_VERBOSE        1
   #else
   # define HARDIRQ_VERBOSE        0
   # define SOFTIRQ_VERBOSE        0
   # define RECLAIM_VERBOSE        0
   #endif
   
   #if VERBOSE || HARDIRQ_VERBOSE || SOFTIRQ_VERBOSE || RECLAIM_VERBOSE
   /*
    * Quick filtering for interesting events:
    */
   static int class_filter(struct lock_class *class)
   {
   #if 0
           /* Example */
           if (class->name_version == 1 &&
                           !strcmp(class->name, "lockname"))
                   return 1;
           if (class->name_version == 1 &&
                           !strcmp(class->name, "&struct->lockfield"))
                   return 1;
   #endif
           /* Filter everything else. 1 would be to allow everything else */
           return 0;
   }
   #endif
   
   static int verbose(struct lock_class *class)
   {
   #if VERBOSE
           return class_filter(class);
   #endif
           return 0;
   }
   
   /*
    * Stack-trace: tightly packed array of stack backtrace
    * addresses. Protected by the graph_lock.
    */
   unsigned long nr_stack_trace_entries;
   static unsigned long stack_trace[MAX_STACK_TRACE_ENTRIES];
   
   static int save_trace(struct stack_trace *trace)
   {
           trace->nr_entries = 0;
           trace->max_entries = MAX_STACK_TRACE_ENTRIES - nr_stack_trace_entries;
           trace->entries = stack_trace + nr_stack_trace_entries;
   
           trace->skip = 3;
   
           save_stack_trace(trace);
   
           /*
            * Some daft arches put -1 at the end to indicate its a full trace.
            *
            * <rant> this is buggy anyway, since it takes a whole extra entry so a
            * complete trace that maxes out the entries provided will be reported
            * as incomplete, friggin useless </rant>
            */
           if (trace->nr_entries != 0 &&
               trace->entries[trace->nr_entries-1] == ULONG_MAX)
                   trace->nr_entries--;
   
           trace->max_entries = trace->nr_entries;
   
           nr_stack_trace_entries += trace->nr_entries;
   
           if (nr_stack_trace_entries >= MAX_STACK_TRACE_ENTRIES-1) {
                   if (!debug_locks_off_graph_unlock())
                           return 0;
   
                   printk("BUG: MAX_STACK_TRACE_ENTRIES too low!\n");
                   printk("turning off the locking correctness validator.\n");
                   dump_stack();
   
                   return 0;
           }
   
           return 1;
   }
   
   unsigned int nr_hardirq_chains;
   unsigned int nr_softirq_chains;
   unsigned int nr_process_chains;
   unsigned int max_lockdep_depth;
   
   #ifdef CONFIG_DEBUG_LOCKDEP
   /*
    * We cannot printk in early bootup code. Not even early_printk()
    * might work. So we mark any initialization errors and printk
    * about it later on, in lockdep_info().
    */
   static int lockdep_init_error;
   static const char *lock_init_error;
   static unsigned long lockdep_init_trace_data[20];
   static struct stack_trace lockdep_init_trace = {
           .max_entries = ARRAY_SIZE(lockdep_init_trace_data),
           .entries = lockdep_init_trace_data,
   };
   
   /*
    * Various lockdep statistics:
    */
   DEFINE_PER_CPU(struct lockdep_stats, lockdep_stats);
   #endif
   
   /*
    * Locking printouts:
    */
   
   #define __USAGE(__STATE)                                                \
           [LOCK_USED_IN_##__STATE] = "IN-"__stringify(__STATE)"-W",       \
           [LOCK_ENABLED_##__STATE] = __stringify(__STATE)"-ON-W",         \
           [LOCK_USED_IN_##__STATE##_READ] = "IN-"__stringify(__STATE)"-R",\
           [LOCK_ENABLED_##__STATE##_READ] = __stringify(__STATE)"-ON-R",
   
   static const char *usage_str[] =
   {
   #define LOCKDEP_STATE(__STATE) __USAGE(__STATE)
   #include "lockdep_states.h"
   #undef LOCKDEP_STATE
           [LOCK_USED] = "INITIAL USE",
   };
   
   const char * __get_key_name(struct lockdep_subclass_key *key, char *str)
   {
           return kallsyms_lookup((unsigned long)key, NULL, NULL, NULL, str);
   }
   
   static inline unsigned long lock_flag(enum lock_usage_bit bit)
   {
           return 1UL << bit;
   }
   
   static char get_usage_char(struct lock_class *class, enum lock_usage_bit bit)
   {
           char c = '.';
   
           if (class->usage_mask & lock_flag(bit + 2))
                   c = '+';
           if (class->usage_mask & lock_flag(bit)) {
                   c = '-';
                   if (class->usage_mask & lock_flag(bit + 2))
                           c = '?';
           }
   
           return c;
   }
   
   void get_usage_chars(struct lock_class *class, char usage[LOCK_USAGE_CHARS])
   {
           int i = 0;
   
   #define LOCKDEP_STATE(__STATE)                                          \
           usage[i++] = get_usage_char(class, LOCK_USED_IN_##__STATE);     \
           usage[i++] = get_usage_char(class, LOCK_USED_IN_##__STATE##_READ);
   #include "lockdep_states.h"
   #undef LOCKDEP_STATE
   
           usage[i] = '\0';
   }
   
   static void __print_lock_name(struct lock_class *class)
   {
           char str[KSYM_NAME_LEN];
           const char *name;
   
           name = class->name;
           if (!name) {
                   name = __get_key_name(class->key, str);
                   printk("%s", name);
           } else {
                   printk("%s", name);
                   if (class->name_version > 1)
                           printk("#%d", class->name_version);
                   if (class->subclass)
                           printk("/%d", class->subclass);
           }
   }
   
   static void print_lock_name(struct lock_class *class)
   {
           char usage[LOCK_USAGE_CHARS];
   
           get_usage_chars(class, usage);
   
           printk(" (");
           __print_lock_name(class);
           printk("){%s}", usage);
   }
   
   static void print_lockdep_cache(struct lockdep_map *lock)
   {
           const char *name;
           char str[KSYM_NAME_LEN];
   
           name = lock->name;
           if (!name)
                   name = __get_key_name(lock->key->subkeys, str);
   
           printk("%s", name);
   }
   
   static void print_lock(struct held_lock *hlock)
   {
           print_lock_name(hlock_class(hlock));
           printk(", at: ");
           print_ip_sym(hlock->acquire_ip);
   }
   
   static void lockdep_print_held_locks(struct task_struct *curr)
   {
           int i, depth = curr->lockdep_depth;
   
           if (!depth) {
                   printk("no locks held by %s/%d.\n", curr->comm, task_pid_nr(curr));
                   return;
           }
           printk("%d lock%s held by %s/%d:\n",
                   depth, depth > 1 ? "s" : "", curr->comm, task_pid_nr(curr));
   
           for (i = 0; i < depth; i++) {
                   printk(" #%d: ", i);
                   print_lock(curr->held_locks + i);
           }
   }
   
   static void print_kernel_ident(void)
   {
           printk("%s %.*s %s\n", init_utsname()->release,
                   (int)strcspn(init_utsname()->version, " "),
                   init_utsname()->version,
                   print_tainted());
   }
   
   static int very_verbose(struct lock_class *class)
   {
   #if VERY_VERBOSE
           return class_filter(class);
   #endif
           return 0;
   }
   
   /*
    * Is this the address of a static object:
    */
   static int static_obj(void *obj)
   {
           unsigned long start = (unsigned long) &_stext,
                         end   = (unsigned long) &_end,
                         addr  = (unsigned long) obj;
   
           /*
            * static variable?
            */
           if ((addr >= start) && (addr < end))
                   return 1;
   
           if (arch_is_kernel_data(addr))
                   return 1;
   
           /*
            * in-kernel percpu var?
            */
           if (is_kernel_percpu_address(addr))
                   return 1;
   
           /*
            * module static or percpu var?
            */
           return is_module_address(addr) || is_module_percpu_address(addr);
   }
   
   /*
    * To make lock name printouts unique, we calculate a unique
    * class->name_version generation counter:
    */
   static int count_matching_names(struct lock_class *new_class)
   {
           struct lock_class *class;
           int count = 0;
   
           if (!new_class->name)
                   return 0;
   
           list_for_each_entry(class, &all_lock_classes, lock_entry) {
                   if (new_class->key - new_class->subclass == class->key)
                           return class->name_version;
                   if (class->name && !strcmp(class->name, new_class->name))
                           count = max(count, class->name_version);
           }
   
           return count + 1;
   }
   
   /*
    * Register a lock's class in the hash-table, if the class is not present
    * yet. Otherwise we look it up. We cache the result in the lock object
    * itself, so actual lookup of the hash should be once per lock object.
    */
   static inline struct lock_class *
   look_up_lock_class(struct lockdep_map *lock, unsigned int subclass)
   {
           struct lockdep_subclass_key *key;
           struct list_head *hash_head;
           struct lock_class *class;
   
   #ifdef CONFIG_DEBUG_LOCKDEP
           /*
            * If the architecture calls into lockdep before initializing
            * the hashes then we'll warn about it later. (we cannot printk
            * right now)
            */
           if (unlikely(!lockdep_initialized)) {
                   lockdep_init();
                   lockdep_init_error = 1;
                   lock_init_error = lock->name;
                   save_stack_trace(&lockdep_init_trace);
           }
   #endif
   
           if (unlikely(subclass >= MAX_LOCKDEP_SUBCLASSES)) {
                   debug_locks_off();
                   printk(KERN_ERR
                           "BUG: looking up invalid subclass: %u\n", subclass);
                   printk(KERN_ERR
                           "turning off the locking correctness validator.\n");
                   dump_stack();
                   return NULL;
           }
   
           /*
            * Static locks do not have their class-keys yet - for them the key
            * is the lock object itself:
            */
           if (unlikely(!lock->key))
                   lock->key = (void *)lock;
   
           /*
            * NOTE: the class-key must be unique. For dynamic locks, a static
            * lock_class_key variable is passed in through the mutex_init()
            * (or spin_lock_init()) call - which acts as the key. For static
            * locks we use the lock object itself as the key.
            */
           BUILD_BUG_ON(sizeof(struct lock_class_key) >
                           sizeof(struct lockdep_map));
   
           key = lock->key->subkeys + subclass;
   
           hash_head = classhashentry(key);
   
           /*
            * We can walk the hash lockfree, because the hash only
            * grows, and we are careful when adding entries to the end:
            */
           list_for_each_entry(class, hash_head, hash_entry) {
                   if (class->key == key) {
                           /*
                            * Huh! same key, different name? Did someone trample
                            * on some memory? We're most confused.
                            */
                           WARN_ON_ONCE(class->name != lock->name);
                           return class;
                   }
           }
   
           return NULL;
   }
   
   /*
    * Register a lock's class in the hash-table, if the class is not present
    * yet. Otherwise we look it up. We cache the result in the lock object
    * itself, so actual lookup of the hash should be once per lock object.
    */
   static inline struct lock_class *
   register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force)
   {
           struct lockdep_subclass_key *key;
           struct list_head *hash_head;
           struct lock_class *class;
           unsigned long flags;
   
           class = look_up_lock_class(lock, subclass);
           if (likely(class))
                   goto out_set_class_cache;
   
           /*
            * Debug-check: all keys must be persistent!
            */
           if (!static_obj(lock->key)) {
                   debug_locks_off();
                   printk("INFO: trying to register non-static key.\n");
                   printk("the code is fine but needs lockdep annotation.\n");
                   printk("turning off the locking correctness validator.\n");
                   dump_stack();
   
                   return NULL;
           }
   
           key = lock->key->subkeys + subclass;
           hash_head = classhashentry(key);
   
           raw_local_irq_save(flags);
           if (!graph_lock()) {
                   raw_local_irq_restore(flags);
                   return NULL;
           }
           /*
            * We have to do the hash-walk again, to avoid races
            * with another CPU:
            */
           list_for_each_entry(class, hash_head, hash_entry)
                   if (class->key == key)
                           goto out_unlock_set;
           /*
            * Allocate a new key from the static array, and add it to
            * the hash:
            */
           if (nr_lock_classes >= MAX_LOCKDEP_KEYS) {
                   if (!debug_locks_off_graph_unlock()) {
                           raw_local_irq_restore(flags);
                           return NULL;
                   }
                   raw_local_irq_restore(flags);
   
                   printk("BUG: MAX_LOCKDEP_KEYS too low!\n");
                   printk("turning off the locking correctness validator.\n");
                   dump_stack();
                   return NULL;
           }
           class = lock_classes + nr_lock_classes++;
           debug_atomic_inc(nr_unused_locks);
           class->key = key;
           class->name = lock->name;
           class->subclass = subclass;
           INIT_LIST_HEAD(&class->lock_entry);
           INIT_LIST_HEAD(&class->locks_before);
           INIT_LIST_HEAD(&class->locks_after);
           class->name_version = count_matching_names(class);
           /*
            * We use RCU's safe list-add method to make
            * parallel walking of the hash-list safe:
            */
           list_add_tail_rcu(&class->hash_entry, hash_head);
           /*
            * Add it to the global list of classes:
            */
           list_add_tail_rcu(&class->lock_entry, &all_lock_classes);
   
           if (verbose(class)) {
                   graph_unlock();
                   raw_local_irq_restore(flags);
   
                   printk("\nnew class %p: %s", class->key, class->name);
                   if (class->name_version > 1)
                           printk("#%d", class->name_version);
                   printk("\n");
                   dump_stack();
   
                   raw_local_irq_save(flags);
                   if (!graph_lock()) {
                           raw_local_irq_restore(flags);
                           return NULL;
                   }
           }
   out_unlock_set:
           graph_unlock();
           raw_local_irq_restore(flags);
   
   out_set_class_cache:
           if (!subclass || force)
                   lock->class_cache[0] = class;
           else if (subclass < NR_LOCKDEP_CACHING_CLASSES)
                   lock->class_cache[subclass] = class;
   
           /*
            * Hash collision, did we smoke some? We found a class with a matching
            * hash but the subclass -- which is hashed in -- didn't match.
            */
           if (DEBUG_LOCKS_WARN_ON(class->subclass != subclass))
                   return NULL;
   
           return class;
   }
   
   #ifdef CONFIG_PROVE_LOCKING
   /*
    * Allocate a lockdep entry. (assumes the graph_lock held, returns
    * with NULL on failure)
    */
   static struct lock_list *alloc_list_entry(void)
   {
           if (nr_list_entries >= MAX_LOCKDEP_ENTRIES) {
                   if (!debug_locks_off_graph_unlock())
                           return NULL;
   
                   printk("BUG: MAX_LOCKDEP_ENTRIES too low!\n");
                   printk("turning off the locking correctness validator.\n");
                   dump_stack();
                   return NULL;
           }
           return list_entries + nr_list_entries++;
   }
   
   /*
    * Add a new dependency to the head of the list:
    */
   static int add_lock_to_list(struct lock_class *class, struct lock_class *this,
                               struct list_head *head, unsigned long ip,
                               int distance, struct stack_trace *trace)
   {
           struct lock_list *entry;
           /*
            * Lock not present yet - get a new dependency struct and
            * add it to the list:
            */
           entry = alloc_list_entry();
           if (!entry)
                   return 0;
   
           entry->class = this;
           entry->distance = distance;
           entry->trace = *trace;
           /*
            * Since we never remove from the dependency list, the list can
            * be walked lockless by other CPUs, it's only allocation
            * that must be protected by the spinlock. But this also means
            * we must make new entries visible only once writes to the
            * entry become visible - hence the RCU op:
            */
           list_add_tail_rcu(&entry->entry, head);
   
           return 1;
   }
   
   /*
    * For good efficiency of modular, we use power of 2
    */
   #define MAX_CIRCULAR_QUEUE_SIZE         4096UL
   #define CQ_MASK                         (MAX_CIRCULAR_QUEUE_SIZE-1)
   
   /*
    * The circular_queue and helpers is used to implement the
    * breadth-first search(BFS)algorithem, by which we can build
    * the shortest path from the next lock to be acquired to the
    * previous held lock if there is a circular between them.
    */
   struct circular_queue {
           unsigned long element[MAX_CIRCULAR_QUEUE_SIZE];
           unsigned int  front, rear;
   };
   
   static struct circular_queue lock_cq;
   
   unsigned int max_bfs_queue_depth;
   
   static unsigned int lockdep_dependency_gen_id;
   
   static inline void __cq_init(struct circular_queue *cq)
   {
           cq->front = cq->rear = 0;
           lockdep_dependency_gen_id++;
   }
   
   static inline int __cq_empty(struct circular_queue *cq)
   {
           return (cq->front == cq->rear);
   }
   
   static inline int __cq_full(struct circular_queue *cq)
   {
           return ((cq->rear + 1) & CQ_MASK) == cq->front;
   }
   
   static inline int __cq_enqueue(struct circular_queue *cq, unsigned long elem)
   {
           if (__cq_full(cq))
                   return -1;
   
           cq->element[cq->rear] = elem;
           cq->rear = (cq->rear + 1) & CQ_MASK;
           return 0;
   }
   
   static inline int __cq_dequeue(struct circular_queue *cq, unsigned long *elem)
   {
           if (__cq_empty(cq))
                   return -1;
   
           *elem = cq->element[cq->front];
           cq->front = (cq->front + 1) & CQ_MASK;
           return 0;
   }
   
   static inline unsigned int  __cq_get_elem_count(struct circular_queue *cq)
   {
           return (cq->rear - cq->front) & CQ_MASK;
   }
   
   static inline void mark_lock_accessed(struct lock_list *lock,
                                           struct lock_list *parent)
   {
           unsigned long nr;
   
           nr = lock - list_entries;
           WARN_ON(nr >= nr_list_entries); /* Out-of-bounds, input fail */
           lock->parent = parent;
           lock->class->dep_gen_id = lockdep_dependency_gen_id;
   }
   
   static inline unsigned long lock_accessed(struct lock_list *lock)
   {
           unsigned long nr;
   
           nr = lock - list_entries;
           WARN_ON(nr >= nr_list_entries); /* Out-of-bounds, input fail */
           return lock->class->dep_gen_id == lockdep_dependency_gen_id;
   }
   
   static inline struct lock_list *get_lock_parent(struct lock_list *child)
   {
           return child->parent;
   }
   
   static inline int get_lock_depth(struct lock_list *child)
   {
           int depth = 0;
           struct lock_list *parent;
   
           while ((parent = get_lock_parent(child))) {
                   child = parent;
                   depth++;
           }
           return depth;
   }
   
   static int __bfs(struct lock_list *source_entry,
                    void *data,
                    int (*match)(struct lock_list *entry, void *data),
                    struct lock_list **target_entry,
                    int forward)
   {
           struct lock_list *entry;
           struct list_head *head;
           struct circular_queue *cq = &lock_cq;
           int ret = 1;
   
           if (match(source_entry, data)) {
                   *target_entry = source_entry;
                   ret = 0;
                   goto exit;
           }
   
           if (forward)
                   head = &source_entry->class->locks_after;
           else
                   head = &source_entry->class->locks_before;
   
           if (list_empty(head))
                  goto exit;
  
          __cq_init(cq);
          __cq_enqueue(cq, (unsigned long)source_entry);
  
          while (!__cq_empty(cq)) {
                  struct lock_list *lock;
  
                  __cq_dequeue(cq, (unsigned long *)&lock);
  
                  if (!lock->class) {
                          ret = -2;
                          goto exit;
                  }
  
                  if (forward)
                          head = &lock->class->locks_after;
                  else
                          head = &lock->class->locks_before;
  
                  list_for_each_entry(entry, head, entry) {
                          if (!lock_accessed(entry)) {
                                  unsigned int cq_depth;
                                  mark_lock_accessed(entry, lock);
                                  if (match(entry, data)) {
                                          *target_entry = entry;
                                          ret = 0;
                                          goto exit;
                                  }
  
                                  if (__cq_enqueue(cq, (unsigned long)entry)) {
                                          ret = -1;
                                          goto exit;
                                  }
                                  cq_depth = __cq_get_elem_count(cq);
                                  if (max_bfs_queue_depth < cq_depth)
                                          max_bfs_queue_depth = cq_depth;
                          }
                  }
          }
  exit:
          return ret;
  }
  
  static inline int __bfs_forwards(struct lock_list *src_entry,
                          void *data,
                          int (*match)(struct lock_list *entry, void *data),
                          struct lock_list **target_entry)
  {
          return __bfs(src_entry, data, match, target_entry, 1);
  
  }
  
  static inline int __bfs_backwards(struct lock_list *src_entry,
                          void *data,
                          int (*match)(struct lock_list *entry, void *data),
                          struct lock_list **target_entry)
  {
          return __bfs(src_entry, data, match, target_entry, 0);
  
  }
  
  /*
   * Recursive, forwards-direction lock-dependency checking, used for
   * both noncyclic checking and for hardirq-unsafe/softirq-unsafe
   * checking.
   */
  
  /*
   * Print a dependency chain entry (this is only done when a deadlock
   * has been detected):
   */
  static noinline int
  print_circular_bug_entry(struct lock_list *target, int depth)
  {
          if (debug_locks_silent)
                  return 0;
          printk("\n-> #%u", depth);
          print_lock_name(target->class);
          printk(":\n");
          print_stack_trace(&target->trace, 6);
  
          return 0;
  }
  
  static void
  print_circular_lock_scenario(struct held_lock *src,
                               struct held_lock *tgt,
                               struct lock_list *prt)
  {
          struct lock_class *source = hlock_class(src);
          struct lock_class *target = hlock_class(tgt);
          struct lock_class *parent = prt->class;
  
          /*
           * A direct locking problem where unsafe_class lock is taken
           * directly by safe_class lock, then all we need to show
           * is the deadlock scenario, as it is obvious that the
           * unsafe lock is taken under the safe lock.
           *
           * But if there is a chain instead, where the safe lock takes
           * an intermediate lock (middle_class) where this lock is
           * not the same as the safe lock, then the lock chain is
           * used to describe the problem. Otherwise we would need
           * to show a different CPU case for each link in the chain
           * from the safe_class lock to the unsafe_class lock.
           */
          if (parent != source) {
                  printk("Chain exists of:\n  ");
                  __print_lock_name(source);
                  printk(" --> ");
                  __print_lock_name(parent);
                  printk(" --> ");
                  __print_lock_name(target);
                  printk("\n\n");
          }
  
          printk(" Possible unsafe locking scenario:\n\n");
          printk("       CPU0                    CPU1\n");
          printk("       ----                    ----\n");
          printk("  lock(");
          __print_lock_name(target);
          printk(");\n");
          printk("                               lock(");
          __print_lock_name(parent);
          printk(");\n");
          printk("                               lock(");
          __print_lock_name(target);
          printk(");\n");
          printk("  lock(");
          __print_lock_name(source);
          printk(");\n");
          printk("\n *** DEADLOCK ***\n\n");
  }
  
  /*
   * When a circular dependency is detected, print the
   * header first:
   */
  static noinline int
  print_circular_bug_header(struct lock_list *entry, unsigned int depth,
                          struct held_lock *check_src,
                          struct held_lock *check_tgt)
  {
          struct task_struct *curr = current;
  
          if (debug_locks_silent)
                  return 0;
  
          printk("\n");
          printk("======================================================\n");
          printk("[ INFO: possible circular locking dependency detected ]\n");
          print_kernel_ident();
          printk("-------------------------------------------------------\n");
          printk("%s/%d is trying to acquire lock:\n",
                  curr->comm, task_pid_nr(curr));
          print_lock(check_src);
          printk("\nbut task is already holding lock:\n");
          print_lock(check_tgt);
          printk("\nwhich lock already depends on the new lock.\n\n");
          printk("\nthe existing dependency chain (in reverse order) is:\n");
  
          print_circular_bug_entry(entry, depth);
  
          return 0;
  }
  
  static inline int class_equal(struct lock_list *entry, void *data)
  {
          return entry->class == data;
  }
  
  static noinline int print_circular_bug(struct lock_list *this,
                                  struct lock_list *target,
                                  struct held_lock *check_src,
                                  struct held_lock *check_tgt)
  {
          struct task_struct *curr = current;
          struct lock_list *parent;
          struct lock_list *first_parent;
          int depth;
  
          if (!debug_locks_off_graph_unlock() || debug_locks_silent)
                  return 0;
  
          if (!save_trace(&this->trace))
                  return 0;
  
          depth = get_lock_depth(target);
  
          print_circular_bug_header(target, depth, check_src, check_tgt);
  
          parent = get_lock_parent(target);
          first_parent = parent;
  
          while (parent) {
                  print_circular_bug_entry(parent, --depth);
                  parent = get_lock_parent(parent);
          }
  
          printk("\nother info that might help us debug this:\n\n");
          print_circular_lock_scenario(check_src, check_tgt,
                                       first_parent);
  
          lockdep_print_held_locks(curr);
  
          printk("\nstack backtrace:\n");
          dump_stack();
  
          return 0;
  }
  
  static noinline int print_bfs_bug(int ret)
  {
          if (!debug_locks_off_graph_unlock())
                  return 0;
  
          /*
           * Breadth-first-search failed, graph got corrupted?
           */
          WARN(1, "lockdep bfs error:%d\n", ret);
  
          return 0;
  }
  
  static int noop_count(struct lock_list *entry, void *data)
  {
          (*(unsigned long *)data)++;
          return 0;
  }
  
  unsigned long __lockdep_count_forward_deps(struct lock_list *this)
  {
          unsigned long  count = 0;
          struct lock_list *uninitialized_var(target_entry);
  
          __bfs_forwards(this, (void *)&count, noop_count, &target_entry);
  
          return count;
  }
  unsigned long lockdep_count_forward_deps(struct lock_class *class)
  {
          unsigned long ret, flags;
          struct lock_list this;
  
          this.parent = NULL;
          this.class = class;
  
          local_irq_save(flags);
          arch_spin_lock(&lockdep_lock);
          ret = __lockdep_count_forward_deps(&this);
          arch_spin_unlock(&lockdep_lock);
          local_irq_restore(flags);
  
          return ret;
  }
  
  unsigned long __lockdep_count_backward_deps(struct lock_list *this)
  {
          unsigned long  count = 0;
          struct lock_list *uninitialized_var(target_entry);
  
          __bfs_backwards(this, (void *)&count, noop_count, &target_entry);
  
          return count;
  }
  
  unsigned long lockdep_count_backward_deps(struct lock_class *class)
  {
          unsigned long ret, flags;
          struct lock_list this;
  
          this.parent = NULL;
          this.class = class;
  
          local_irq_save(flags);
          arch_spin_lock(&lockdep_lock);
          ret = __lockdep_count_backward_deps(&this);
          arch_spin_unlock(&lockdep_lock);
          local_irq_restore(flags);
  
          return ret;
  }
  
  /*
   * Prove that the dependency graph starting at <entry> can not
   * lead to <target>. Print an error and return 0 if it does.
   */
  static noinline int
  check_noncircular(struct lock_list *root, struct lock_class *target,
                  struct lock_list **target_entry)
  {
          int result;
  
          debug_atomic_inc(nr_cyclic_checks);
  
          result = __bfs_forwards(root, target, class_equal, target_entry);
  
          return result;
  }
  
  #if defined(CONFIG_TRACE_IRQFLAGS) && defined(CONFIG_PROVE_LOCKING)
  /*
   * Forwards and backwards subgraph searching, for the purposes of
   * proving that two subgraphs can be connected by a new dependency
   * without creating any illegal irq-safe -> irq-unsafe lock dependency.
   */
  
  static inline int usage_match(struct lock_list *entry, void *bit)
  {
          return entry->class->usage_mask & (1 << (enum lock_usage_bit)bit);
  }
  
  
  
  /*
   * Find a node in the forwards-direction dependency sub-graph starting
   * at @root->class that matches @bit.
   *
   * Return 0 if such a node exists in the subgraph, and put that node
   * into *@target_entry.
   *
   * Return 1 otherwise and keep *@target_entry unchanged.
   * Return <0 on error.
   */
  static int
  find_usage_forwards(struct lock_list *root, enum lock_usage_bit bit,
                          struct lock_list **target_entry)
  {
          int result;
  
          debug_atomic_inc(nr_find_usage_forwards_checks);
  
          result = __bfs_forwards(root, (void *)bit, usage_match, target_entry);
  
          return result;
  }
  
  /*
   * Find a node in the backwards-direction dependency sub-graph starting
   * at @root->class that matches @bit.
   *
   * Return 0 if such a node exists in the subgraph, and put that node
   * into *@target_entry.
   *
   * Return 1 otherwise and keep *@target_entry unchanged.
   * Return <0 on error.
   */
  static int
  find_usage_backwards(struct lock_list *root, enum lock_usage_bit bit,
                          struct lock_list **target_entry)
  {
          int result;
  
          debug_atomic_inc(nr_find_usage_backwards_checks);
  
          result = __bfs_backwards(root, (void *)bit, usage_match, target_entry);
  
          return result;
  }
  
  static void print_lock_class_header(struct lock_class *class, int depth)
  {
          int bit;
  
          printk("%*s->", depth, "");
          print_lock_name(class);
          printk(" ops: %lu", class->ops);
          printk(" {\n");
  
          for (bit = 0; bit < LOCK_USAGE_STATES; bit++) {
                  if (class->usage_mask & (1 << bit)) {
                          int len = depth;
  
                          len += printk("%*s   %s", depth, "", usage_str[bit]);
                          len += printk(" at:\n");
                          print_stack_trace(class->usage_traces + bit, len);
                  }
          }
          printk("%*s }\n", depth, "");
  
          printk("%*s ... key      at: ",depth,"");
          print_ip_sym((unsigned long)class->key);
  }
  
  /*
   * printk the shortest lock dependencies from @start to @end in reverse order:
   */
  static void __used
  print_shortest_lock_dependencies(struct lock_list *leaf,
                                  struct lock_list *root)
  {
          struct lock_list *entry = leaf;
          int depth;
  
          /*compute depth from generated tree by BFS*/
          depth = get_lock_depth(leaf);
  
          do {
                  print_lock_class_header(entry->class, depth);
                  printk("%*s ... acquired at:\n", depth, "");
                  print_stack_trace(&entry->trace, 2);
                  printk("\n");
  
                  if (depth == 0 && (entry != root)) {
                          printk("lockdep:%s bad path found in chain graph\n", __func__);
                          break;
                  }
  
                  entry = get_lock_parent(entry);
                  depth--;
          } while (entry && (depth >= 0));
  
          return;
  }
  
  static void
  print_irq_lock_scenario(struct lock_list *safe_entry,
                          struct lock_list *unsafe_entry,
                          struct lock_class *prev_class,
                          struct lock_class *next_class)
  {
          struct lock_class *safe_class = safe_entry->class;
          struct lock_class *unsafe_class = unsafe_entry->class;
          struct lock_class *middle_class = prev_class;
  
          if (middle_class == safe_class)
                  middle_class = next_class;
  
          /*
           * A direct locking problem where unsafe_class lock is taken
           * directly by safe_class lock, then all we need to show
           * is the deadlock scenario, as it is obvious that the
           * unsafe lock is taken under the safe lock.
           *
           * But if there is a chain instead, where the safe lock takes
           * an intermediate lock (middle_class) where this lock is
           * not the same as the safe lock, then the lock chain is
           * used to describe the problem. Otherwise we would need
           * to show a different CPU case for each link in the chain
           * from the safe_class lock to the unsafe_class lock.
           */
          if (middle_class != unsafe_class) {
                  printk("Chain exists of:\n  ");
                  __print_lock_name(safe_class);
                  printk(" --> ");
                  __print_lock_name(middle_class);
                  printk(" --> ");
                  __print_lock_name(unsafe_class);
                  printk("\n\n");
          }
  
          printk(" Possible interrupt unsafe locking scenario:\n\n");
          printk("       CPU0                    CPU1\n");
          printk("       ----                    ----\n");
          printk("  lock(");
          __print_lock_name(unsafe_class);
          printk(");\n");
          printk("                               local_irq_disable();\n");
          printk("                               lock(");
          __print_lock_name(safe_class);
          printk(");\n");
          printk("                               lock(");
          __print_lock_name(middle_class);
          printk(");\n");
          printk("  <Interrupt>\n");
          printk("    lock(");
          __print_lock_name(safe_class);
          printk(");\n");
          printk("\n *** DEADLOCK ***\n\n");
  }
  
  static int
  print_bad_irq_dependency(struct task_struct *curr,
                           struct lock_list *prev_root,
                           struct lock_list *next_root,
                           struct lock_list *backwards_entry,
                           struct lock_list *forwards_entry,
                           struct held_lock *prev,
                           struct held_lock *next,
                           enum lock_usage_bit bit1,
                           enum lock_usage_bit bit2,
                           const char *irqclass)
  {
          if (!debug_locks_off_graph_unlock() || debug_locks_silent)
                  return 0;
  
          printk("\n");
          printk("======================================================\n");
          printk("[ INFO: %s-safe -> %s-unsafe lock order detected ]\n",
                  irqclass, irqclass);
          print_kernel_ident();
          printk("------------------------------------------------------\n");
          printk("%s/%d [HC%u[%lu]:SC%u[%lu]:HE%u:SE%u] is trying to acquire:\n",
                  curr->comm, task_pid_nr(curr),
                  curr->hardirq_context, hardirq_count() >> HARDIRQ_SHIFT,
                  curr->softirq_context, softirq_count() >> SOFTIRQ_SHIFT,
                  curr->hardirqs_enabled,
                  curr->softirqs_enabled);
          print_lock(next);
  
          printk("\nand this task is already holding:\n");
          print_lock(prev);
          printk("which would create a new lock dependency:\n");
          print_lock_name(hlock_class(prev));
          printk(" ->");
          print_lock_name(hlock_class(next));
          printk("\n");
  
          printk("\nbut this new dependency connects a %s-irq-safe lock:\n",
                  irqclass);
          print_lock_name(backwards_entry->class);
          printk("\n... which became %s-irq-safe at:\n", irqclass);
  
          print_stack_trace(backwards_entry->class->usage_traces + bit1, 1);
  
          printk("\nto a %s-irq-unsafe lock:\n", irqclass);
          print_lock_name(forwards_entry->class);
          printk("\n... which became %s-irq-unsafe at:\n", irqclass);
          printk("...");
  
          print_stack_trace(forwards_entry->class->usage_traces + bit2, 1);
  
          printk("\nother info that might help us debug this:\n\n");
          print_irq_lock_scenario(backwards_entry, forwards_entry,
                                  hlock_class(prev), hlock_class(next));
  
          lockdep_print_held_locks(curr);
  
          printk("\nthe dependencies between %s-irq-safe lock", irqclass);
          printk(" and the holding lock:\n");
          if (!save_trace(&prev_root->trace))
                  return 0;
          print_shortest_lock_dependencies(backwards_entry, prev_root);
  
          printk("\nthe dependencies between the lock to be acquired");
          printk(" and %s-irq-unsafe lock:\n", irqclass);
          if (!save_trace(&next_root->trace))
                  return 0;
          print_shortest_lock_dependencies(forwards_entry, next_root);
  
          printk("\nstack backtrace:\n");
          dump_stack();
  
          return 0;
  }
  
  static int
  check_usage(struct task_struct *curr, struct held_lock *prev,
              struct held_lock *next, enum lock_usage_bit bit_backwards,
              enum lock_usage_bit bit_forwards, const char *irqclass)
  {
          int ret;
          struct lock_list this, that;
          struct lock_list *uninitialized_var(target_entry);
          struct lock_list *uninitialized_var(target_entry1);
  
          this.parent = NULL;
  
          this.class = hlock_class(prev);
          ret = find_usage_backwards(&this, bit_backwards, &target_entry);
          if (ret < 0)
                  return print_bfs_bug(ret);
          if (ret == 1)
                  return ret;
  
          that.parent = NULL;
          that.class = hlock_class(next);
          ret = find_usage_forwards(&that, bit_forwards, &target_entry1);
          if (ret < 0)
                  return print_bfs_bug(ret);
          if (ret == 1)
                  return ret;
  
          return print_bad_irq_dependency(curr, &this, &that,
                          target_entry, target_entry1,
                          prev, next,
                          bit_backwards, bit_forwards, irqclass);
  }
  
  static const char *state_names[] = {
  #define LOCKDEP_STATE(__STATE) \
          __stringify(__STATE),
  #include "lockdep_states.h"
  #undef LOCKDEP_STATE
  };
  
  static const char *state_rnames[] = {
  #define LOCKDEP_STATE(__STATE) \
          __stringify(__STATE)"-READ",
  #include "lockdep_states.h"
  #undef LOCKDEP_STATE
  };
  
  static inline const char *state_name(enum lock_usage_bit bit)
  {
          return (bit & 1) ? state_rnames[bit >> 2] : state_names[bit >> 2];
  }
  
  static int exclusive_bit(int new_bit)
  {
          /*
           * USED_IN
           * USED_IN_READ
           * ENABLED
           * ENABLED_READ
           *
           * bit 0 - write/read
           * bit 1 - used_in/enabled
           * bit 2+  state
           */
  
          int state = new_bit & ~3;
          int dir = new_bit & 2;
  
          /*
           * keep state, bit flip the direction and strip read.
           */
          return state | (dir ^ 2);
  }
  
  static int check_irq_usage(struct task_struct *curr, struct held_lock *prev,
                             struct held_lock *next, enum lock_usage_bit bit)
  {
          /*
           * Prove that the new dependency does not connect a hardirq-safe
           * lock with a hardirq-unsafe lock - to achieve this we search
           * the backwards-subgraph starting at <prev>, and the
           * forwards-subgraph starting at <next>:
           */
          if (!check_usage(curr, prev, next, bit,
                             exclusive_bit(bit), state_name(bit)))
                  return 0;
  
          bit++; /* _READ */
  
          /*
           * Prove that the new dependency does not connect a hardirq-safe-read
           * lock with a hardirq-unsafe lock - to achieve this we search
           * the backwards-subgraph starting at <prev>, and the
           * forwards-subgraph starting at <next>:
           */
          if (!check_usage(curr, prev, next, bit,
                             exclusive_bit(bit), state_name(bit)))
                  return 0;
  
          return 1;
  }
  
  static int
  check_prev_add_irq(struct task_struct *curr, struct held_lock *prev,
                  struct held_lock *next)
  {
  #define LOCKDEP_STATE(__STATE)                                          \
          if (!check_irq_usage(curr, prev, next, LOCK_USED_IN_##__STATE)) \
                  return 0;
  #include "lockdep_states.h"
  #undef LOCKDEP_STATE
  
          return 1;
  }
  
  static void inc_chains(void)
  {
          if (current->hardirq_context)
                  nr_hardirq_chains++;
          else {
                  if (current->softirq_context)
                          nr_softirq_chains++;
                  else
                          nr_process_chains++;
          }
  }
  
  #else
  
  static inline int
  check_prev_add_irq(struct task_struct *curr, struct held_lock *prev,
                  struct held_lock *next)
  {
          return 1;
  }
  
  static inline void inc_chains(void)
  {
          nr_process_chains++;
  }
  
  #endif
  
  static void
  print_deadlock_scenario(struct held_lock *nxt,
                               struct held_lock *prv)
  {
          struct lock_class *next = hlock_class(nxt);
          struct lock_class *prev = hlock_class(prv);
  
          printk(" Possible unsafe locking scenario:\n\n");
          printk("       CPU0\n");
          printk("       ----\n");
          printk("  lock(");
          __print_lock_name(prev);
          printk(");\n");
          printk("  lock(");
          __print_lock_name(next);
          printk(");\n");
          printk("\n *** DEADLOCK ***\n\n");
          printk(" May be due to missing lock nesting notation\n\n");
  }
  
  static int
  print_deadlock_bug(struct task_struct *curr, struct held_lock *prev,
                     struct held_lock *next)
  {
          if (!debug_locks_off_graph_unlock() || debug_locks_silent)
                  return 0;
  
          printk("\n");
          printk("=============================================\n");
          printk("[ INFO: possible recursive locking detected ]\n");
          print_kernel_ident();
          printk("---------------------------------------------\n");
          printk("%s/%d is trying to acquire lock:\n",
                  curr->comm, task_pid_nr(curr));
          print_lock(next);
          printk("\nbut task is already holding lock:\n");
          print_lock(prev);
  
          printk("\nother info that might help us debug this:\n");
          print_deadlock_scenario(next, prev);
          lockdep_print_held_locks(curr);
  
          printk("\nstack backtrace:\n");
          dump_stack();
  
          return 0;
  }
  
  /*
   * Check whether we are holding such a class already.
   *
   * (Note that this has to be done separately, because the graph cannot
   * detect such classes of deadlocks.)
   *
   * Returns: 0 on deadlock detected, 1 on OK, 2 on recursive read
   */
  static int
  check_deadlock(struct task_struct *curr, struct held_lock *next,
                 struct lockdep_map *next_instance, int read)
  {
          struct held_lock *prev;
          struct held_lock *nest = NULL;
          int i;
  
          for (i = 0; i < curr->lockdep_depth; i++) {
                  prev = curr->held_locks + i;
  
                  if (prev->instance == next->nest_lock)
                          nest = prev;
  
                  if (hlock_class(prev) != hlock_class(next))
                          continue;
  
                  /*
                   * Allow read-after-read recursion of the same
                   * lock class (i.e. read_lock(lock)+read_lock(lock)):
                   */
                  if ((read == 2) && prev->read)
                          return 2;
  
                  /*
                   * We're holding the nest_lock, which serializes this lock's
                   * nesting behaviour.
                   */
                  if (nest)
                          return 2;
  
                  return print_deadlock_bug(curr, prev, next);
          }
          return 1;
  }
  
  /*
   * There was a chain-cache miss, and we are about to add a new dependency
   * to a previous lock. We recursively validate the following rules:
   *
   *  - would the adding of the <prev> -> <next> dependency create a
   *    circular dependency in the graph? [== circular deadlock]
   *
   *  - does the new prev->next dependency connect any hardirq-safe lock
   *    (in the full backwards-subgraph starting at <prev>) with any
   *    hardirq-unsafe lock (in the full forwards-subgraph starting at
   *    <next>)? [== illegal lock inversion with hardirq contexts]
   *
   *  - does the new prev->next dependency connect any softirq-safe lock
   *    (in the full backwards-subgraph starting at <prev>) with any
   *    softirq-unsafe lock (in the full forwards-subgraph starting at
   *    <next>)? [== illegal lock inversion with softirq contexts]
   *
   * any of these scenarios could lead to a deadlock.
   *
   * Then if all the validations pass, we add the forwards and backwards
   * dependency.
   */
  static int
  check_prev_add(struct task_struct *curr, struct held_lock *prev,
                 struct held_lock *next, int distance, int trylock_loop)
  {
          struct lock_list *entry;
          int ret;
          struct lock_list this;
          struct lock_list *uninitialized_var(target_entry);
          /*
           * Static variable, serialized by the graph_lock().
           *
           * We use this static variable to save the stack trace in case
           * we call into this function multiple times due to encountering
           * trylocks in the held lock stack.
           */
          static struct stack_trace trace;
  
          /*
           * Prove that the new <prev> -> <next> dependency would not
           * create a circular dependency in the graph. (We do this by
           * forward-recursing into the graph starting at <next>, and
           * checking whether we can reach <prev>.)
           *
           * We are using global variables to control the recursion, to
           * keep the stackframe size of the recursive functions low:
           */
          this.class = hlock_class(next);
          this.parent = NULL;
          ret = check_noncircular(&this, hlock_class(prev), &target_entry);
          if (unlikely(!ret))
                  return print_circular_bug(&this, target_entry, next, prev);
          else if (unlikely(ret < 0))
                  return print_bfs_bug(ret);
  
          if (!check_prev_add_irq(curr, prev, next))
                  return 0;
  
          /*
           * For recursive read-locks we do all the dependency checks,
           * but we dont store read-triggered dependencies (only
           * write-triggered dependencies). This ensures that only the
           * write-side dependencies matter, and that if for example a
           * write-lock never takes any other locks, then the reads are
           * equivalent to a NOP.
           */
          if (next->read == 2 || prev->read == 2)
                  return 1;
          /*
           * Is the <prev> -> <next> dependency already present?
           *
           * (this may occur even though this is a new chain: consider
           *  e.g. the L1 -> L2 -> L3 -> L4 and the L5 -> L1 -> L2 -> L3
           *  chains - the second one will be new, but L1 already has
           *  L2 added to its dependency list, due to the first chain.)
           */
          list_for_each_entry(entry, &hlock_class(prev)->locks_after, entry) {
                  if (entry->class == hlock_class(next)) {
                          if (distance == 1)
                                  entry->distance = 1;
                          return 2;
                  }
          }
  
          if (!trylock_loop && !save_trace(&trace))
                  return 0;
  
          /*
           * Ok, all validations passed, add the new lock
           * to the previous lock's dependency list:
           */
          ret = add_lock_to_list(hlock_class(prev), hlock_class(next),
                                 &hlock_class(prev)->locks_after,
                                 next->acquire_ip, distance, &trace);
  
          if (!ret)
                  return 0;
  
          ret = add_lock_to_list(hlock_class(next), hlock_class(prev),
                                 &hlock_class(next)->locks_before,
                                 next->acquire_ip, distance, &trace);
          if (!ret)
                  return 0;
  
          /*
           * Debugging printouts:
           */
          if (verbose(hlock_class(prev)) || verbose(hlock_class(next))) {
                  graph_unlock();
                  printk("\n new dependency: ");
                  print_lock_name(hlock_class(prev));
                  printk(" => ");
                  print_lock_name(hlock_class(next));
                  printk("\n");
                  dump_stack();
                  return graph_lock();
          }
          return 1;
  }
  
  /*
   * Add the dependency to all directly-previous locks that are 'relevant'.
   * The ones that are relevant are (in increasing distance from curr):
   * all consecutive trylock entries and the final non-trylock entry - or
   * the end of this context's lock-chain - whichever comes first.
   */
  static int
  check_prevs_add(struct task_struct *curr, struct held_lock *next)
  {
          int depth = curr->lockdep_depth;
          int trylock_loop = 0;
          struct held_lock *hlock;
  
          /*
           * Debugging checks.
           *
           * Depth must not be zero for a non-head lock:
           */
          if (!depth)
                  goto out_bug;
          /*
           * At least two relevant locks must exist for this
           * to be a head:
           */
          if (curr->held_locks[depth].irq_context !=
                          curr->held_locks[depth-1].irq_context)
                  goto out_bug;
  
          for (;;) {
                  int distance = curr->lockdep_depth - depth + 1;
                  hlock = curr->held_locks + depth-1;
                  /*
                   * Only non-recursive-read entries get new dependencies
                   * added:
                   */
                  if (hlock->read != 2) {
                          if (!check_prev_add(curr, hlock, next,
                                                  distance, trylock_loop))
                                  return 0;
                          /*
                           * Stop after the first non-trylock entry,
                           * as non-trylock entries have added their
                           * own direct dependencies already, so this
                           * lock is connected to them indirectly:
                           */
                          if (!hlock->trylock)
                                  break;
                  }
                  depth--;
                  /*
                   * End of lock-stack?
                   */
                  if (!depth)
                          break;
                  /*
                   * Stop the search if we cross into another context:
                   */
                  if (curr->held_locks[depth].irq_context !=
                                  curr->held_locks[depth-1].irq_context)
                          break;
                  trylock_loop = 1;
          }
          return 1;
  out_bug:
          if (!debug_locks_off_graph_unlock())
                  return 0;
  
          /*
           * Clearly we all shouldn't be here, but since we made it we
           * can reliable say we messed up our state. See the above two
           * gotos for reasons why we could possibly end up here.
           */
          WARN_ON(1);
  
          return 0;
  }
  
  unsigned long nr_lock_chains;
  struct lock_chain lock_chains[MAX_LOCKDEP_CHAINS];
  int nr_chain_hlocks;
  static u16 chain_hlocks[MAX_LOCKDEP_CHAIN_HLOCKS];
  
  struct lock_class *lock_chain_get_class(struct lock_chain *chain, int i)
  {
          return lock_classes + chain_hlocks[chain->base + i];
  }
  
  /*
   * Look up a dependency chain. If the key is not present yet then
   * add it and return 1 - in this case the new dependency chain is
   * validated. If the key is already hashed, return 0.
   * (On return with 1 graph_lock is held.)
   */
  static inline int lookup_chain_cache(struct task_struct *curr,
                                       struct held_lock *hlock,
                                       u64 chain_key)
  {
          struct lock_class *class = hlock_class(hlock);
          struct list_head *hash_head = chainhashentry(chain_key);
          struct lock_chain *chain;
          struct held_lock *hlock_curr, *hlock_next;
          int i, j;
  
          /*
           * We might need to take the graph lock, ensure we've got IRQs
           * disabled to make this an IRQ-safe lock.. for recursion reasons
           * lockdep won't complain about its own locking errors.
           */
          if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
                  return 0;
          /*
           * We can walk it lock-free, because entries only get added
           * to the hash:
           */
          list_for_each_entry(chain, hash_head, entry) {
                  if (chain->chain_key == chain_key) {
  cache_hit:
                          debug_atomic_inc(chain_lookup_hits);
                          if (very_verbose(class))
                                  printk("\nhash chain already cached, key: "
                                          "%016Lx tail class: [%p] %s\n",
                                          (unsigned long long)chain_key,
                                          class->key, class->name);
                          return 0;
                  }
          }
          if (very_verbose(class))
                  printk("\nnew hash chain, key: %016Lx tail class: [%p] %s\n",
                          (unsigned long long)chain_key, class->key, class->name);
          /*
           * Allocate a new chain entry from the static array, and add
           * it to the hash:
           */
          if (!graph_lock())
                  return 0;
          /*
           * We have to walk the chain again locked - to avoid duplicates:
           */
          list_for_each_entry(chain, hash_head, entry) {
                  if (chain->chain_key == chain_key) {
                          graph_unlock();
                          goto cache_hit;
                  }
          }
          if (unlikely(nr_lock_chains >= MAX_LOCKDEP_CHAINS)) {
                  if (!debug_locks_off_graph_unlock())
                          return 0;
  
                  printk("BUG: MAX_LOCKDEP_CHAINS too low!\n");
                  printk("turning off the locking correctness validator.\n");
                  dump_stack();
                  return 0;
          }
          chain = lock_chains + nr_lock_chains++;
          chain->chain_key = chain_key;
          chain->irq_context = hlock->irq_context;
          /* Find the first held_lock of current chain */
          hlock_next = hlock;
          for (i = curr->lockdep_depth - 1; i >= 0; i--) {
                  hlock_curr = curr->held_locks + i;
                  if (hlock_curr->irq_context != hlock_next->irq_context)
                          break;
                  hlock_next = hlock;
          }
          i++;
          chain->depth = curr->lockdep_depth + 1 - i;
          if (likely(nr_chain_hlocks + chain->depth <= MAX_LOCKDEP_CHAIN_HLOCKS)) {
                  chain->base = nr_chain_hlocks;
                  nr_chain_hlocks += chain->depth;
                  for (j = 0; j < chain->depth - 1; j++, i++) {
                          int lock_id = curr->held_locks[i].class_idx - 1;
                          chain_hlocks[chain->base + j] = lock_id;
                  }
                  chain_hlocks[chain->base + j] = class - lock_classes;
          }
          list_add_tail_rcu(&chain->entry, hash_head);
          debug_atomic_inc(chain_lookup_misses);
          inc_chains();
  
          return 1;
  }
  
  static int validate_chain(struct task_struct *curr, struct lockdep_map *lock,
                  struct held_lock *hlock, int chain_head, u64 chain_key)
  {
          /*
           * Trylock needs to maintain the stack of held locks, but it
           * does not add new dependencies, because trylock can be done
           * in any order.
           *
           * We look up the chain_key and do the O(N^2) check and update of
           * the dependencies only if this is a new dependency chain.
           * (If lookup_chain_cache() returns with 1 it acquires
           * graph_lock for us)
           */
          if (!hlock->trylock && (hlock->check == 2) &&
              lookup_chain_cache(curr, hlock, chain_key)) {
                  /*
                   * Check whether last held lock:
                   *
                   * - is irq-safe, if this lock is irq-unsafe
                   * - is softirq-safe, if this lock is hardirq-unsafe
                   *
                   * And check whether the new lock's dependency graph
                   * could lead back to the previous lock.
                   *
                   * any of these scenarios could lead to a deadlock. If
                   * All validations
                   */
                  int ret = check_deadlock(curr, hlock, lock, hlock->read);
  
                  if (!ret)
                          return 0;
                  /*
                   * Mark recursive read, as we jump over it when
                   * building dependencies (just like we jump over
                   * trylock entries):
                   */
                  if (ret == 2)
                          hlock->read = 2;
                  /*
                   * Add dependency only if this lock is not the head
                   * of the chain, and if it's not a secondary read-lock:
                   */
                  if (!chain_head && ret != 2)
                          if (!check_prevs_add(curr, hlock))
                                  return 0;
                  graph_unlock();
          } else
                  /* after lookup_chain_cache(): */
                  if (unlikely(!debug_locks))
                          return 0;
  
          return 1;
  }
  #else
  static inline int validate_chain(struct task_struct *curr,
                  struct lockdep_map *lock, struct held_lock *hlock,
                  int chain_head, u64 chain_key)
  {
          return 1;
  }
  #endif
  
  /*
   * We are building curr_chain_key incrementally, so double-check
   * it from scratch, to make sure that it's done correctly:
   */
  static void check_chain_key(struct task_struct *curr)
  {
  #ifdef CONFIG_DEBUG_LOCKDEP
          struct held_lock *hlock, *prev_hlock = NULL;
          unsigned int i, id;
          u64 chain_key = 0;
  
          for (i = 0; i < curr->lockdep_depth; i++) {
                  hlock = curr->held_locks + i;
                  if (chain_key != hlock->prev_chain_key) {
                          debug_locks_off();
                          /*
                           * We got mighty confused, our chain keys don't match
                           * with what we expect, someone trample on our task state?
                           */
                          WARN(1, "hm#1, depth: %u [%u], %016Lx != %016Lx\n",
                                  curr->lockdep_depth, i,
                                  (unsigned long long)chain_key,
                                  (unsigned long long)hlock->prev_chain_key);
                          return;
                  }
                  id = hlock->class_idx - 1;
                  /*
                   * Whoops ran out of static storage again?
                   */
                  if (DEBUG_LOCKS_WARN_ON(id >= MAX_LOCKDEP_KEYS))
                          return;
  
                  if (prev_hlock && (prev_hlock->irq_context !=
                                                          hlock->irq_context))
                          chain_key = 0;
                  chain_key = iterate_chain_key(chain_key, id);
                  prev_hlock = hlock;
          }
          if (chain_key != curr->curr_chain_key) {
                  debug_locks_off();
                  /*
                   * More smoking hash instead of calculating it, damn see these
                   * numbers float.. I bet that a pink elephant stepped on my memory.
                   */
                  WARN(1, "hm#2, depth: %u [%u], %016Lx != %016Lx\n",
                          curr->lockdep_depth, i,
                          (unsigned long long)chain_key,
                          (unsigned long long)curr->curr_chain_key);
          }
  #endif
  }
  
  static void
  print_usage_bug_scenario(struct held_lock *lock)
  {
          struct lock_class *class = hlock_class(lock);
  
          printk(" Possible unsafe locking scenario:\n\n");
          printk("       CPU0\n");
          printk("       ----\n");
          printk("  lock(");
          __print_lock_name(class);
          printk(");\n");
          printk("  <Interrupt>\n");
          printk("    lock(");
          __print_lock_name(class);
          printk(");\n");
          printk("\n *** DEADLOCK ***\n\n");
  }
  
  static int
  print_usage_bug(struct task_struct *curr, struct held_lock *this,
                  enum lock_usage_bit prev_bit, enum lock_usage_bit new_bit)
  {
          if (!debug_locks_off_graph_unlock() || debug_locks_silent)
                  return 0;
  
          printk("\n");
          printk("=================================\n");
          printk("[ INFO: inconsistent lock state ]\n");
          print_kernel_ident();
          printk("---------------------------------\n");
  
          printk("inconsistent {%s} -> {%s} usage.\n",
                  usage_str[prev_bit], usage_str[new_bit]);
  
          printk("%s/%d [HC%u[%lu]:SC%u[%lu]:HE%u:SE%u] takes:\n",
                  curr->comm, task_pid_nr(curr),
                  trace_hardirq_context(curr), hardirq_count() >> HARDIRQ_SHIFT,
                  trace_softirq_context(curr), softirq_count() >> SOFTIRQ_SHIFT,
                  trace_hardirqs_enabled(curr),
                  trace_softirqs_enabled(curr));
          print_lock(this);
  
          printk("{%s} state was registered at:\n", usage_str[prev_bit]);
          print_stack_trace(hlock_class(this)->usage_traces + prev_bit, 1);
  
          print_irqtrace_events(curr);
          printk("\nother info that might help us debug this:\n");
          print_usage_bug_scenario(this);
  
          lockdep_print_held_locks(curr);
  
          printk("\nstack backtrace:\n");
          dump_stack();
  
          return 0;
  }
  
  /*
   * Print out an error if an invalid bit is set:
   */
  static inline int
  valid_state(struct task_struct *curr, struct held_lock *this,
              enum lock_usage_bit new_bit, enum lock_usage_bit bad_bit)
  {
          if (unlikely(hlock_class(this)->usage_mask & (1 << bad_bit)))
                  return print_usage_bug(curr, this, bad_bit, new_bit);
          return 1;
  }
  
  static int mark_lock(struct task_struct *curr, struct held_lock *this,
                       enum lock_usage_bit new_bit);
  
  #if defined(CONFIG_TRACE_IRQFLAGS) && defined(CONFIG_PROVE_LOCKING)
  
  /*
   * print irq inversion bug:
   */
  static int
  print_irq_inversion_bug(struct task_struct *curr,
                          struct lock_list *root, struct lock_list *other,
                          struct held_lock *this, int forwards,
                          const char *irqclass)
  {
          struct lock_list *entry = other;
          struct lock_list *middle = NULL;
          int depth;
  
          if (!debug_locks_off_graph_unlock() || debug_locks_silent)
                  return 0;
  
          printk("\n");
          printk("=========================================================\n");
          printk("[ INFO: possible irq lock inversion dependency detected ]\n");
          print_kernel_ident();
          printk("---------------------------------------------------------\n");
          printk("%s/%d just changed the state of lock:\n",
                  curr->comm, task_pid_nr(curr));
          print_lock(this);
          if (forwards)
                  printk("but this lock took another, %s-unsafe lock in the past:\n", irqclass);
          else
                  printk("but this lock was taken by another, %s-safe lock in the past:\n", irqclass);
          print_lock_name(other->class);
          printk("\n\nand interrupts could create inverse lock ordering between them.\n\n");
  
          printk("\nother info that might help us debug this:\n");
  
          /* Find a middle lock (if one exists) */
          depth = get_lock_depth(other);
          do {
                  if (depth == 0 && (entry != root)) {
                          printk("lockdep:%s bad path found in chain graph\n", __func__);
                          break;
                  }
                  middle = entry;
                  entry = get_lock_parent(entry);
                  depth--;
          } while (entry && entry != root && (depth >= 0));
          if (forwards)
                  print_irq_lock_scenario(root, other,
                          middle ? middle->class : root->class, other->class);
          else
                  print_irq_lock_scenario(other, root,
                          middle ? middle->class : other->class, root->class);
  
          lockdep_print_held_locks(curr);
  
          printk("\nthe shortest dependencies between 2nd lock and 1st lock:\n");
          if (!save_trace(&root->trace))
                  return 0;
          print_shortest_lock_dependencies(other, root);
  
          printk("\nstack backtrace:\n");
          dump_stack();
  
          return 0;
  }
  
  /*
   * Prove that in the forwards-direction subgraph starting at <this>
   * there is no lock matching <mask>:
   */
  static int
  check_usage_forwards(struct task_struct *curr, struct held_lock *this,
                       enum lock_usage_bit bit, const char *irqclass)
  {
          int ret;
          struct lock_list root;
          struct lock_list *uninitialized_var(target_entry);
  
          root.parent = NULL;
          root.class = hlock_class(this);
          ret = find_usage_forwards(&root, bit, &target_entry);
          if (ret < 0)
                  return print_bfs_bug(ret);
          if (ret == 1)
                  return ret;
  
          return print_irq_inversion_bug(curr, &root, target_entry,
                                          this, 1, irqclass);
  }
  
  /*
   * Prove that in the backwards-direction subgraph starting at <this>
   * there is no lock matching <mask>:
   */
  static int
  check_usage_backwards(struct task_struct *curr, struct held_lock *this,
                        enum lock_usage_bit bit, const char *irqclass)
  {
          int ret;
          struct lock_list root;
          struct lock_list *uninitialized_var(target_entry);
  
          root.parent = NULL;
          root.class = hlock_class(this);
          ret = find_usage_backwards(&root, bit, &target_entry);
          if (ret < 0)
                  return print_bfs_bug(ret);
          if (ret == 1)
                  return ret;
  
          return print_irq_inversion_bug(curr, &root, target_entry,
                                          this, 0, irqclass);
  }
  
  void print_irqtrace_events(struct task_struct *curr)
  {
          printk("irq event stamp: %u\n", curr->irq_events);
          printk("hardirqs last  enabled at (%u): ", curr->hardirq_enable_event);
          print_ip_sym(curr->hardirq_enable_ip);
          printk("hardirqs last disabled at (%u): ", curr->hardirq_disable_event);
          print_ip_sym(curr->hardirq_disable_ip);
          printk("softirqs last  enabled at (%u): ", curr->softirq_enable_event);
          print_ip_sym(curr->softirq_enable_ip);
          printk("softirqs last disabled at (%u): ", curr->softirq_disable_event);
          print_ip_sym(curr->softirq_disable_ip);
  }
  
  static int HARDIRQ_verbose(struct lock_class *class)
  {
  #if HARDIRQ_VERBOSE
          return class_filter(class);
  #endif
          return 0;
  }
  
  static int SOFTIRQ_verbose(struct lock_class *class)
  {
  #if SOFTIRQ_VERBOSE
          return class_filter(class);
  #endif
          return 0;
  }
  
  static int RECLAIM_FS_verbose(struct lock_class *class)
  {
  #if RECLAIM_VERBOSE
          return class_filter(class);
  #endif
          return 0;
  }
  
  #define STRICT_READ_CHECKS      1
  
  static int (*state_verbose_f[])(struct lock_class *class) = {
  #define LOCKDEP_STATE(__STATE) \
          __STATE##_verbose,
  #include "lockdep_states.h"
  #undef LOCKDEP_STATE
  };
  
  static inline int state_verbose(enum lock_usage_bit bit,
                                  struct lock_class *class)
  {
          return state_verbose_f[bit >> 2](class);
  }
  
  typedef int (*check_usage_f)(struct task_struct *, struct held_lock *,
                               enum lock_usage_bit bit, const char *name);
  
  static int
  mark_lock_irq(struct task_struct *curr, struct held_lock *this,
                  enum lock_usage_bit new_bit)
  {
          int excl_bit = exclusive_bit(new_bit);
          int read = new_bit & 1;
          int dir = new_bit & 2;
  
          /*
           * mark USED_IN has to look forwards -- to ensure no dependency
           * has ENABLED state, which would allow recursion deadlocks.
           *
           * mark ENABLED has to look backwards -- to ensure no dependee
           * has USED_IN state, which, again, would allow  recursion deadlocks.
           */
          check_usage_f usage = dir ?
                  check_usage_backwards : check_usage_forwards;
  
          /*
           * Validate that this particular lock does not have conflicting
           * usage states.
           */
          if (!valid_state(curr, this, new_bit, excl_bit))
                  return 0;
  
          /*
           * Validate that the lock dependencies don't have conflicting usage
           * states.
           */
          if ((!read || !dir || STRICT_READ_CHECKS) &&
                          !usage(curr, this, excl_bit, state_name(new_bit & ~1)))
                  return 0;
  
          /*
           * Check for read in write conflicts
           */
          if (!read) {
                  if (!valid_state(curr, this, new_bit, excl_bit + 1))
                          return 0;
  
                  if (STRICT_READ_CHECKS &&
                          !usage(curr, this, excl_bit + 1,
                                  state_name(new_bit + 1)))
                          return 0;
          }
  
          if (state_verbose(new_bit, hlock_class(this)))
                  return 2;
  
          return 1;
  }
  
  enum mark_type {
  #define LOCKDEP_STATE(__STATE)  __STATE,
  #include "lockdep_states.h"
  #undef LOCKDEP_STATE
  };
  
  /*
   * Mark all held locks with a usage bit:
   */
  static int
  mark_held_locks(struct task_struct *curr, enum mark_type mark)
  {
          enum lock_usage_bit usage_bit;
          struct held_lock *hlock;
          int i;
  
          for (i = 0; i < curr->lockdep_depth; i++) {
                  hlock = curr->held_locks + i;
  
                  usage_bit = 2 + (mark << 2); /* ENABLED */
                  if (hlock->read)
                          usage_bit += 1; /* READ */
  
                  BUG_ON(usage_bit >= LOCK_USAGE_STATES);
  
                  if (hlock_class(hlock)->key == __lockdep_no_validate__.subkeys)
                          continue;
  
                  if (!mark_lock(curr, hlock, usage_bit))
                          return 0;
          }
  
          return 1;
  }
  
  /*
   * Hardirqs will be enabled:
   */
  static void __trace_hardirqs_on_caller(unsigned long ip)
  {
          struct task_struct *curr = current;
  
          /* we'll do an OFF -> ON transition: */
          curr->hardirqs_enabled = 1;
  
          /*
           * We are going to turn hardirqs on, so set the
           * usage bit for all held locks:
           */
          if (!mark_held_locks(curr, HARDIRQ))
                  return;
          /*
           * If we have softirqs enabled, then set the usage
           * bit for all held locks. (disabled hardirqs prevented
           * this bit from being set before)
           */
          if (curr->softirqs_enabled)
                  if (!mark_held_locks(curr, SOFTIRQ))
                          return;
  
          curr->hardirq_enable_ip = ip;
          curr->hardirq_enable_event = ++curr->irq_events;
          debug_atomic_inc(hardirqs_on_events);
  }
  
  void trace_hardirqs_on_caller(unsigned long ip)
  {
          time_hardirqs_on(CALLER_ADDR0, ip);
  
          if (unlikely(!debug_locks || current->lockdep_recursion))
                  return;
  
          if (unlikely(current->hardirqs_enabled)) {
                  /*
                   * Neither irq nor preemption are disabled here
                   * so this is racy by nature but losing one hit
                   * in a stat is not a big deal.
                   */
                  __debug_atomic_inc(redundant_hardirqs_on);
                  return;
          }
  
          /*
           * We're enabling irqs and according to our state above irqs weren't
           * already enabled, yet we find the hardware thinks they are in fact
           * enabled.. someone messed up their IRQ state tracing.
           */
          if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
                  return;
  
          /*
           * See the fine text that goes along with this variable definition.
           */
          if (DEBUG_LOCKS_WARN_ON(unlikely(early_boot_irqs_disabled)))
                  return;
  
          /*
           * Can't allow enabling interrupts while in an interrupt handler,
           * that's general bad form and such. Recursion, limited stack etc..
           */
          if (DEBUG_LOCKS_WARN_ON(current->hardirq_context))
                  return;
  
          current->lockdep_recursion = 1;
          __trace_hardirqs_on_caller(ip);
          current->lockdep_recursion = 0;
  }
  EXPORT_SYMBOL(trace_hardirqs_on_caller);
  
  void trace_hardirqs_on(void)
  {
          trace_hardirqs_on_caller(CALLER_ADDR0);
  }
  EXPORT_SYMBOL(trace_hardirqs_on);
  
  /*
   * Hardirqs were disabled:
   */
  void trace_hardirqs_off_caller(unsigned long ip)
  {
          struct task_struct *curr = current;
  
          time_hardirqs_off(CALLER_ADDR0, ip);
  
          if (unlikely(!debug_locks || current->lockdep_recursion))
                  return;
  
          /*
           * So we're supposed to get called after you mask local IRQs, but for
           * some reason the hardware doesn't quite think you did a proper job.
           */
          if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
                  return;
  
          if (curr->hardirqs_enabled) {
                  /*
                   * We have done an ON -> OFF transition:
                   */
                  curr->hardirqs_enabled = 0;
                  curr->hardirq_disable_ip = ip;
                  curr->hardirq_disable_event = ++curr->irq_events;
                  debug_atomic_inc(hardirqs_off_events);
          } else
                  debug_atomic_inc(redundant_hardirqs_off);
  }
  EXPORT_SYMBOL(trace_hardirqs_off_caller);
  
  void trace_hardirqs_off(void)
  {
          trace_hardirqs_off_caller(CALLER_ADDR0);
  }
  EXPORT_SYMBOL(trace_hardirqs_off);
  
  /*
   * Softirqs will be enabled:
   */
  void trace_softirqs_on(unsigned long ip)
  {
          struct task_struct *curr = current;
  
          if (unlikely(!debug_locks || current->lockdep_recursion))
                  return;
  
          /*
           * We fancy IRQs being disabled here, see softirq.c, avoids
           * funny state and nesting things.
           */
          if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
                  return;
  
          if (curr->softirqs_enabled) {
                  debug_atomic_inc(redundant_softirqs_on);
                  return;
          }
  
          current->lockdep_recursion = 1;
          /*
           * We'll do an OFF -> ON transition:
           */
          curr->softirqs_enabled = 1;
          curr->softirq_enable_ip = ip;
          curr->softirq_enable_event = ++curr->irq_events;
          debug_atomic_inc(softirqs_on_events);
          /*
           * We are going to turn softirqs on, so set the
           * usage bit for all held locks, if hardirqs are
           * enabled too:
           */
          if (curr->hardirqs_enabled)
                  mark_held_locks(curr, SOFTIRQ);
          current->lockdep_recursion = 0;
  }
  
  /*
   * Softirqs were disabled:
   */
  void trace_softirqs_off(unsigned long ip)
  {
          struct task_struct *curr = current;
  
          if (unlikely(!debug_locks || current->lockdep_recursion))
                  return;
  
          /*
           * We fancy IRQs being disabled here, see softirq.c
           */
          if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
                  return;
  
          if (curr->softirqs_enabled) {
                  /*
                   * We have done an ON -> OFF transition:
                   */
                  curr->softirqs_enabled = 0;
                  curr->softirq_disable_ip = ip;
                  curr->softirq_disable_event = ++curr->irq_events;
                  debug_atomic_inc(softirqs_off_events);
                  /*
                   * Whoops, we wanted softirqs off, so why aren't they?
                   */
                  DEBUG_LOCKS_WARN_ON(!softirq_count());
          } else
                  debug_atomic_inc(redundant_softirqs_off);
  }
  
  static void __lockdep_trace_alloc(gfp_t gfp_mask, unsigned long flags)
  {
          struct task_struct *curr = current;
  
          if (unlikely(!debug_locks))
                  return;
  
          /* no reclaim without waiting on it */
          if (!(gfp_mask & __GFP_WAIT))
                  return;
  
          /* this guy won't enter reclaim */
          if ((curr->flags & PF_MEMALLOC) && !(gfp_mask & __GFP_NOMEMALLOC))
                  return;
  
          /* We're only interested __GFP_FS allocations for now */
          if (!(gfp_mask & __GFP_FS))
                  return;
  
          /*
           * Oi! Can't be having __GFP_FS allocations with IRQs disabled.
           */
          if (DEBUG_LOCKS_WARN_ON(irqs_disabled_flags(flags)))
                  return;
  
          mark_held_locks(curr, RECLAIM_FS);
  }
  
  static void check_flags(unsigned long flags);
  
  void lockdep_trace_alloc(gfp_t gfp_mask)
  {
          unsigned long flags;
  
          if (unlikely(current->lockdep_recursion))
                  return;
  
          raw_local_irq_save(flags);
          check_flags(flags);
          current->lockdep_recursion = 1;
          __lockdep_trace_alloc(gfp_mask, flags);
          current->lockdep_recursion = 0;
          raw_local_irq_restore(flags);
  }
  
  static int mark_irqflags(struct task_struct *curr, struct held_lock *hlock)
  {
          /*
           * If non-trylock use in a hardirq or softirq context, then
           * mark the lock as used in these contexts:
           */
          if (!hlock->trylock) {
                  if (hlock->read) {
                          if (curr->hardirq_context)
                                  if (!mark_lock(curr, hlock,
                                                  LOCK_USED_IN_HARDIRQ_READ))
                                          return 0;
                          if (curr->softirq_context)
                                  if (!mark_lock(curr, hlock,
                                                  LOCK_USED_IN_SOFTIRQ_READ))
                                          return 0;
                  } else {
                          if (curr->hardirq_context)
                                  if (!mark_lock(curr, hlock, LOCK_USED_IN_HARDIRQ))
                                          return 0;
                          if (curr->softirq_context)
                                  if (!mark_lock(curr, hlock, LOCK_USED_IN_SOFTIRQ))
                                          return 0;
                  }
          }
          if (!hlock->hardirqs_off) {
                  if (hlock->read) {
                          if (!mark_lock(curr, hlock,
                                          LOCK_ENABLED_HARDIRQ_READ))
                                  return 0;
                          if (curr->softirqs_enabled)
                                  if (!mark_lock(curr, hlock,
                                                  LOCK_ENABLED_SOFTIRQ_READ))
                                          return 0;
                  } else {
                          if (!mark_lock(curr, hlock,
                                          LOCK_ENABLED_HARDIRQ))
                                  return 0;
                          if (curr->softirqs_enabled)
                                  if (!mark_lock(curr, hlock,
                                                  LOCK_ENABLED_SOFTIRQ))
                                          return 0;
                  }
          }
  
          /*
           * We reuse the irq context infrastructure more broadly as a general
           * context checking code. This tests GFP_FS recursion (a lock taken
           * during reclaim for a GFP_FS allocation is held over a GFP_FS
           * allocation).
           */
          if (!hlock->trylock && (curr->lockdep_reclaim_gfp & __GFP_FS)) {
                  if (hlock->read) {
                          if (!mark_lock(curr, hlock, LOCK_USED_IN_RECLAIM_FS_READ))
                                          return 0;
                  } else {
                          if (!mark_lock(curr, hlock, LOCK_USED_IN_RECLAIM_FS))
                                          return 0;
                  }
          }
  
          return 1;
  }
  
  static int separate_irq_context(struct task_struct *curr,
                  struct held_lock *hlock)
  {
          unsigned int depth = curr->lockdep_depth;
  
          /*
           * Keep track of points where we cross into an interrupt context:
           */
          hlock->irq_context = 2*(curr->hardirq_context ? 1 : 0) +
                                  curr->softirq_context;
          if (depth) {
                  struct held_lock *prev_hlock;
  
                  prev_hlock = curr->held_locks + depth-1;
                  /*
                   * If we cross into another context, reset the
                   * hash key (this also prevents the checking and the
                   * adding of the dependency to 'prev'):
                   */
                  if (prev_hlock->irq_context != hlock->irq_context)
                          return 1;
          }
          return 0;
  }
  
  #else /* defined(CONFIG_TRACE_IRQFLAGS) && defined(CONFIG_PROVE_LOCKING) */
  
  static inline
  int mark_lock_irq(struct task_struct *curr, struct held_lock *this,
                  enum lock_usage_bit new_bit)
  {
          WARN_ON(1); /* Impossible innit? when we don't have TRACE_IRQFLAG */
          return 1;
  }
  
  static inline int mark_irqflags(struct task_struct *curr,
                  struct held_lock *hlock)
  {
          return 1;
  }
  
  static inline int separate_irq_context(struct task_struct *curr,
                  struct held_lock *hlock)
  {
          return 0;
  }
  
  void lockdep_trace_alloc(gfp_t gfp_mask)
  {
  }
  
  #endif /* defined(CONFIG_TRACE_IRQFLAGS) && defined(CONFIG_PROVE_LOCKING) */
  
  /*
   * Mark a lock with a usage bit, and validate the state transition:
   */
  static int mark_lock(struct task_struct *curr, struct held_lock *this,
                               enum lock_usage_bit new_bit)
  {
          unsigned int new_mask = 1 << new_bit, ret = 1;
  
          /*
           * If already set then do not dirty the cacheline,
           * nor do any checks:
           */
          if (likely(hlock_class(this)->usage_mask & new_mask))
                  return 1;
  
          if (!graph_lock())
                  return 0;
          /*
           * Make sure we didn't race:
           */
          if (unlikely(hlock_class(this)->usage_mask & new_mask)) {
                  graph_unlock();
                  return 1;
          }
  
          hlock_class(this)->usage_mask |= new_mask;
  
          if (!save_trace(hlock_class(this)->usage_traces + new_bit))
                  return 0;
  
          switch (new_bit) {
  #define LOCKDEP_STATE(__STATE)                  \
          case LOCK_USED_IN_##__STATE:            \
          case LOCK_USED_IN_##__STATE##_READ:     \
          case LOCK_ENABLED_##__STATE:            \
          case LOCK_ENABLED_##__STATE##_READ:
  #include "lockdep_states.h"
  #undef LOCKDEP_STATE
                  ret = mark_lock_irq(curr, this, new_bit);
                  if (!ret)
                          return 0;
                  break;
          case LOCK_USED:
                  debug_atomic_dec(nr_unused_locks);
                  break;
          default:
                  if (!debug_locks_off_graph_unlock())
                          return 0;
                  WARN_ON(1);
                  return 0;
          }
  
          graph_unlock();
  
          /*
           * We must printk outside of the graph_lock:
           */
          if (ret == 2) {
                  printk("\nmarked lock as {%s}:\n", usage_str[new_bit]);
                  print_lock(this);
                  print_irqtrace_events(curr);
                  dump_stack();
          }
  
          return ret;
  }
  
  /*
   * Initialize a lock instance's lock-class mapping info:
   */
  void lockdep_init_map(struct lockdep_map *lock, const char *name,
                        struct lock_class_key *key, int subclass)
  {
          int i;
  
          kmemcheck_mark_initialized(lock, sizeof(*lock));
  
          for (i = 0; i < NR_LOCKDEP_CACHING_CLASSES; i++)
                  lock->class_cache[i] = NULL;
  
  #ifdef CONFIG_LOCK_STAT
          lock->cpu = raw_smp_processor_id();
  #endif
  
          /*
           * Can't be having no nameless bastards around this place!
           */
          if (DEBUG_LOCKS_WARN_ON(!name)) {
                  lock->name = "NULL";
                  return;
          }
  
          lock->name = name;
  
          /*
           * No key, no joy, we need to hash something.
           */
          if (DEBUG_LOCKS_WARN_ON(!key))
                  return;
          /*
           * Sanity check, the lock-class key must be persistent:
           */
          if (!static_obj(key)) {
                  printk("BUG: key %p not in .data!\n", key);
                  /*
                   * What it says above ^^^^^, I suggest you read it.
                   */
                  DEBUG_LOCKS_WARN_ON(1);
                  return;
          }
          lock->key = key;
  
          if (unlikely(!debug_locks))
                  return;
  
          if (subclass)
                  register_lock_class(lock, subclass, 1);
  }
  EXPORT_SYMBOL_GPL(lockdep_init_map);
  
  struct lock_class_key __lockdep_no_validate__;
  
  static int
  print_lock_nested_lock_not_held(struct task_struct *curr,
                                  struct held_lock *hlock,
                                  unsigned long ip)
  {
          if (!debug_locks_off())
                  return 0;
          if (debug_locks_silent)
                  return 0;
  
          printk("\n");
          printk("==================================\n");
          printk("[ BUG: Nested lock was not taken ]\n");
          print_kernel_ident();
          printk("----------------------------------\n");
  
          printk("%s/%d is trying to lock:\n", curr->comm, task_pid_nr(curr));
          print_lock(hlock);
  
          printk("\nbut this task is not holding:\n");
          printk("%s\n", hlock->nest_lock->name);
  
          printk("\nstack backtrace:\n");
          dump_stack();
  
          printk("\nother info that might help us debug this:\n");
          lockdep_print_held_locks(curr);
  
          printk("\nstack backtrace:\n");
          dump_stack();
  
          return 0;
  }
  
  static int __lock_is_held(struct lockdep_map *lock);
  
  /*
   * This gets called for every mutex_lock*()/spin_lock*() operation.
   * We maintain the dependency maps and validate the locking attempt:
   */
  static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
                            int trylock, int read, int check, int hardirqs_off,
                            struct lockdep_map *nest_lock, unsigned long ip,
                            int references)
  {
          struct task_struct *curr = current;
          struct lock_class *class = NULL;
          struct held_lock *hlock;
          unsigned int depth, id;
          int chain_head = 0;
          int class_idx;
          u64 chain_key;
  
          if (!prove_locking)
                  check = 1;
  
          if (unlikely(!debug_locks))
                  return 0;
  
          /*
           * Lockdep should run with IRQs disabled, otherwise we could
           * get an interrupt which would want to take locks, which would
           * end up in lockdep and have you got a head-ache already?
           */
          if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
                  return 0;
  
          if (lock->key == &__lockdep_no_validate__)
                  check = 1;
  
          if (subclass < NR_LOCKDEP_CACHING_CLASSES)
                  class = lock->class_cache[subclass];
          /*
           * Not cached?
           */
          if (unlikely(!class)) {
                  class = register_lock_class(lock, subclass, 0);
                  if (!class)
                          return 0;
          }
          atomic_inc((atomic_t *)&class->ops);
          if (very_verbose(class)) {
                  printk("\nacquire class [%p] %s", class->key, class->name);
                  if (class->name_version > 1)
                          printk("#%d", class->name_version);
                  printk("\n");
                  dump_stack();
          }
  
          /*
           * Add the lock to the list of currently held locks.
           * (we dont increase the depth just yet, up until the
           * dependency checks are done)
           */
          depth = curr->lockdep_depth;
          /*
           * Ran out of static storage for our per-task lock stack again have we?
           */
          if (DEBUG_LOCKS_WARN_ON(depth >= MAX_LOCK_DEPTH))
                  return 0;
  
          class_idx = class - lock_classes + 1;
  
          if (depth) {
                  hlock = curr->held_locks + depth - 1;
                  if (hlock->class_idx == class_idx && nest_lock) {
                          if (hlock->references)
                                  hlock->references++;
                          else
                                  hlock->references = 2;
  
                          return 1;
                  }
          }
  
          hlock = curr->held_locks + depth;
          /*
           * Plain impossible, we just registered it and checked it weren't no
           * NULL like.. I bet this mushroom I ate was good!
           */
          if (DEBUG_LOCKS_WARN_ON(!class))
                  return 0;
          hlock->class_idx = class_idx;
          hlock->acquire_ip = ip;
          hlock->instance = lock;
          hlock->nest_lock = nest_lock;
          hlock->trylock = trylock;
          hlock->read = read;
          hlock->check = check;
          hlock->hardirqs_off = !!hardirqs_off;
          hlock->references = references;
  #ifdef CONFIG_LOCK_STAT
          hlock->waittime_stamp = 0;
          hlock->holdtime_stamp = lockstat_clock();
  #endif
  
          if (check == 2 && !mark_irqflags(curr, hlock))
                  return 0;
  
          /* mark it as used: */
          if (!mark_lock(curr, hlock, LOCK_USED))
                  return 0;
  
          /*
           * Calculate the chain hash: it's the combined hash of all the
           * lock keys along the dependency chain. We save the hash value
           * at every step so that we can get the current hash easily
           * after unlock. The chain hash is then used to cache dependency
           * results.
           *
           * The 'key ID' is what is the most compact key value to drive
           * the hash, not class->key.
           */
          id = class - lock_classes;
          /*
           * Whoops, we did it again.. ran straight out of our static allocation.
           */
          if (DEBUG_LOCKS_WARN_ON(id >= MAX_LOCKDEP_KEYS))
                  return 0;
  
          chain_key = curr->curr_chain_key;
          if (!depth) {
                  /*
                   * How can we have a chain hash when we ain't got no keys?!
                   */
                  if (DEBUG_LOCKS_WARN_ON(chain_key != 0))
                          return 0;
                  chain_head = 1;
          }
  
          hlock->prev_chain_key = chain_key;
          if (separate_irq_context(curr, hlock)) {
                  chain_key = 0;
                  chain_head = 1;
          }
          chain_key = iterate_chain_key(chain_key, id);
  
          if (nest_lock && !__lock_is_held(nest_lock))
                  return print_lock_nested_lock_not_held(curr, hlock, ip);
  
          if (!validate_chain(curr, lock, hlock, chain_head, chain_key))
                  return 0;
  
          curr->curr_chain_key = chain_key;
          curr->lockdep_depth++;
          check_chain_key(curr);
  #ifdef CONFIG_DEBUG_LOCKDEP
          if (unlikely(!debug_locks))
                  return 0;
  #endif
          if (unlikely(curr->lockdep_depth >= MAX_LOCK_DEPTH)) {
                  debug_locks_off();
                  printk("BUG: MAX_LOCK_DEPTH too low!\n");
                  printk("turning off the locking correctness validator.\n");
                  dump_stack();
                  return 0;
          }
  
          if (unlikely(curr->lockdep_depth > max_lockdep_depth))
                  max_lockdep_depth = curr->lockdep_depth;
  
          return 1;
  }
  
  static int
  print_unlock_inbalance_bug(struct task_struct *curr, struct lockdep_map *lock,
                             unsigned long ip)
  {
          if (!debug_locks_off())
                  return 0;
          if (debug_locks_silent)
                  return 0;
  
          printk("\n");
          printk("=====================================\n");
          printk("[ BUG: bad unlock balance detected! ]\n");
          print_kernel_ident();
          printk("-------------------------------------\n");
          printk("%s/%d is trying to release lock (",
                  curr->comm, task_pid_nr(curr));
          print_lockdep_cache(lock);
          printk(") at:\n");
          print_ip_sym(ip);
          printk("but there are no more locks to release!\n");
          printk("\nother info that might help us debug this:\n");
          lockdep_print_held_locks(curr);
  
          printk("\nstack backtrace:\n");
          dump_stack();
  
          return 0;
  }
  
  /*
   * Common debugging checks for both nested and non-nested unlock:
   */
  static int check_unlock(struct task_struct *curr, struct lockdep_map *lock,
                          unsigned long ip)
  {
          if (unlikely(!debug_locks))
                  return 0;
          /*
           * Lockdep should run with IRQs disabled, recursion, head-ache, etc..
           */
          if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
                  return 0;
  
          if (curr->lockdep_depth <= 0)
                  return print_unlock_inbalance_bug(curr, lock, ip);
  
          return 1;
  }
  
  static int match_held_lock(struct held_lock *hlock, struct lockdep_map *lock)
  {
          if (hlock->instance == lock)
                  return 1;
  
          if (hlock->references) {
                  struct lock_class *class = lock->class_cache[0];
  
                  if (!class)
                          class = look_up_lock_class(lock, 0);
  
                  /*
                   * If look_up_lock_class() failed to find a class, we're trying
                   * to test if we hold a lock that has never yet been acquired.
                   * Clearly if the lock hasn't been acquired _ever_, we're not
                   * holding it either, so report failure.
                   */
                  if (!class)
                          return 0;
  
                  /*
                   * References, but not a lock we're actually ref-counting?
                   * State got messed up, follow the sites that change ->references
                   * and try to make sense of it.
                   */
                  if (DEBUG_LOCKS_WARN_ON(!hlock->nest_lock))
                          return 0;
  
                  if (hlock->class_idx == class - lock_classes + 1)
                          return 1;
          }
  
          return 0;
  }
  
  static int
  __lock_set_class(struct lockdep_map *lock, const char *name,
                   struct lock_class_key *key, unsigned int subclass,
                   unsigned long ip)
  {
          struct task_struct *curr = current;
          struct held_lock *hlock, *prev_hlock;
          struct lock_class *class;
          unsigned int depth;
          int i;
  
          depth = curr->lockdep_depth;
          /*
           * This function is about (re)setting the class of a held lock,
           * yet we're not actually holding any locks. Naughty user!
           */
          if (DEBUG_LOCKS_WARN_ON(!depth))
                  return 0;
  
          prev_hlock = NULL;
          for (i = depth-1; i >= 0; i--) {
                  hlock = curr->held_locks + i;
                  /*
                   * We must not cross into another context:
                   */
                  if (prev_hlock && prev_hlock->irq_context != hlock->irq_context)
                          break;
                  if (match_held_lock(hlock, lock))
                          goto found_it;
                  prev_hlock = hlock;
          }
          return print_unlock_inbalance_bug(curr, lock, ip);
  
  found_it:
          lockdep_init_map(lock, name, key, 0);
          class = register_lock_class(lock, subclass, 0);
          hlock->class_idx = class - lock_classes + 1;
  
          curr->lockdep_depth = i;
          curr->curr_chain_key = hlock->prev_chain_key;
  
          for (; i < depth; i++) {
                  hlock = curr->held_locks + i;
                  if (!__lock_acquire(hlock->instance,
                          hlock_class(hlock)->subclass, hlock->trylock,
                                  hlock->read, hlock->check, hlock->hardirqs_off,
                                  hlock->nest_lock, hlock->acquire_ip,
                                  hlock->references))
                          return 0;
          }
  
          /*
           * I took it apart and put it back together again, except now I have
           * these 'spare' parts.. where shall I put them.
           */
          if (DEBUG_LOCKS_WARN_ON(curr->lockdep_depth != depth))
                  return 0;
          return 1;
  }
  
  /*
   * Remove the lock to the list of currently held locks in a
   * potentially non-nested (out of order) manner. This is a
   * relatively rare operation, as all the unlock APIs default
   * to nested mode (which uses lock_release()):
   */
  static int
  lock_release_non_nested(struct task_struct *curr,
                          struct lockdep_map *lock, unsigned long ip)
  {
          struct held_lock *hlock, *prev_hlock;
          unsigned int depth;
          int i;
  
          /*
           * Check whether the lock exists in the current stack
           * of held locks:
           */
          depth = curr->lockdep_depth;
          /*
           * So we're all set to release this lock.. wait what lock? We don't
           * own any locks, you've been drinking again?
           */
          if (DEBUG_LOCKS_WARN_ON(!depth))
                  return 0;
  
          prev_hlock = NULL;
          for (i = depth-1; i >= 0; i--) {
                  hlock = curr->held_locks + i;
                  /*
                   * We must not cross into another context:
                   */
                  if (prev_hlock && prev_hlock->irq_context != hlock->irq_context)
                          break;
                  if (match_held_lock(hlock, lock))
                          goto found_it;
                  prev_hlock = hlock;
          }
          return print_unlock_inbalance_bug(curr, lock, ip);
  
  found_it:
          if (hlock->instance == lock)
                  lock_release_holdtime(hlock);
  
          if (hlock->references) {
                  hlock->references--;
                  if (hlock->references) {
                          /*
                           * We had, and after removing one, still have
                           * references, the current lock stack is still
                           * valid. We're done!
                           */
                          return 1;
                  }
          }
  
          /*
           * We have the right lock to unlock, 'hlock' points to it.
           * Now we remove it from the stack, and add back the other
           * entries (if any), recalculating the hash along the way:
           */
  
          curr->lockdep_depth = i;
          curr->curr_chain_key = hlock->prev_chain_key;
  
          for (i++; i < depth; i++) {
                  hlock = curr->held_locks + i;
                  if (!__lock_acquire(hlock->instance,
                          hlock_class(hlock)->subclass, hlock->trylock,
                                  hlock->read, hlock->check, hlock->hardirqs_off,
                                  hlock->nest_lock, hlock->acquire_ip,
                                  hlock->references))
                          return 0;
          }
  
          /*
           * We had N bottles of beer on the wall, we drank one, but now
           * there's not N-1 bottles of beer left on the wall...
           */
          if (DEBUG_LOCKS_WARN_ON(curr->lockdep_depth != depth - 1))
                  return 0;
          return 1;
  }
  
  /*
   * Remove the lock to the list of currently held locks - this gets
   * called on mutex_unlock()/spin_unlock*() (or on a failed
   * mutex_lock_interruptible()). This is done for unlocks that nest
   * perfectly. (i.e. the current top of the lock-stack is unlocked)
   */
  static int lock_release_nested(struct task_struct *curr,
                                 struct lockdep_map *lock, unsigned long ip)
  {
          struct held_lock *hlock;
          unsigned int depth;
  
          /*
           * Pop off the top of the lock stack:
           */
          depth = curr->lockdep_depth - 1;
          hlock = curr->held_locks + depth;
  
          /*
           * Is the unlock non-nested:
           */
          if (hlock->instance != lock || hlock->references)
                  return lock_release_non_nested(curr, lock, ip);
          curr->lockdep_depth--;
  
          /*
           * No more locks, but somehow we've got hash left over, who left it?
           */
          if (DEBUG_LOCKS_WARN_ON(!depth && (hlock->prev_chain_key != 0)))
                  return 0;
  
          curr->curr_chain_key = hlock->prev_chain_key;
  
          lock_release_holdtime(hlock);
  
  #ifdef CONFIG_DEBUG_LOCKDEP
          hlock->prev_chain_key = 0;
          hlock->class_idx = 0;
          hlock->acquire_ip = 0;
          hlock->irq_context = 0;
  #endif
          return 1;
  }
  
  /*
   * Remove the lock to the list of currently held locks - this gets
   * called on mutex_unlock()/spin_unlock*() (or on a failed
   * mutex_lock_interruptible()). This is done for unlocks that nest
   * perfectly. (i.e. the current top of the lock-stack is unlocked)
   */
  static void
  __lock_release(struct lockdep_map *lock, int nested, unsigned long ip)
  {
          struct task_struct *curr = current;
  
          if (!check_unlock(curr, lock, ip))
                  return;
  
          if (nested) {
                  if (!lock_release_nested(curr, lock, ip))
                          return;
          } else {
                  if (!lock_release_non_nested(curr, lock, ip))
                          return;
          }
  
          check_chain_key(curr);
  }
  
  static int __lock_is_held(struct lockdep_map *lock)
  {
          struct task_struct *curr = current;
          int i;
  
          for (i = 0; i < curr->lockdep_depth; i++) {
                  struct held_lock *hlock = curr->held_locks + i;
  
                  if (match_held_lock(hlock, lock))
                          return 1;
          }
  
          return 0;
  }
  
  /*
   * Check whether we follow the irq-flags state precisely:
   */
  static void check_flags(unsigned long flags)
  {
  #if defined(CONFIG_PROVE_LOCKING) && defined(CONFIG_DEBUG_LOCKDEP) && \
      defined(CONFIG_TRACE_IRQFLAGS)
          if (!debug_locks)
                  return;
  
          if (irqs_disabled_flags(flags)) {
                  if (DEBUG_LOCKS_WARN_ON(current->hardirqs_enabled)) {
                          printk("possible reason: unannotated irqs-off.\n");
                  }
          } else {
                  if (DEBUG_LOCKS_WARN_ON(!current->hardirqs_enabled)) {
                          printk("possible reason: unannotated irqs-on.\n");
                  }
          }
  
          /*
           * We dont accurately track softirq state in e.g.
           * hardirq contexts (such as on 4KSTACKS), so only
           * check if not in hardirq contexts:
           */
          if (!hardirq_count()) {
                  if (softirq_count()) {
                          /* like the above, but with softirqs */
                          DEBUG_LOCKS_WARN_ON(current->softirqs_enabled);
                  } else {
                          /* lick the above, does it taste good? */
                          DEBUG_LOCKS_WARN_ON(!current->softirqs_enabled);
                  }
          }
  
          if (!debug_locks)
                  print_irqtrace_events(current);
  #endif
  }
  
  void lock_set_class(struct lockdep_map *lock, const char *name,
                      struct lock_class_key *key, unsigned int subclass,
                      unsigned long ip)
  {
          unsigned long flags;
  
          if (unlikely(current->lockdep_recursion))
                  return;
  
          raw_local_irq_save(flags);
          current->lockdep_recursion = 1;
          check_flags(flags);
          if (__lock_set_class(lock, name, key, subclass, ip))
                  check_chain_key(current);
          current->lockdep_recursion = 0;
          raw_local_irq_restore(flags);
  }
  EXPORT_SYMBOL_GPL(lock_set_class);
  
  /*
   * We are not always called with irqs disabled - do that here,
   * and also avoid lockdep recursion:
   */
  void lock_acquire(struct lockdep_map *lock, unsigned int subclass,
                            int trylock, int read, int check,
                            struct lockdep_map *nest_lock, unsigned long ip)
  {
          unsigned long flags;
  
          if (unlikely(current->lockdep_recursion))
                  return;
  
          raw_local_irq_save(flags);
          check_flags(flags);
  
          current->lockdep_recursion = 1;
          trace_lock_acquire(lock, subclass, trylock, read, check, nest_lock, ip);
          __lock_acquire(lock, subclass, trylock, read, check,
                         irqs_disabled_flags(flags), nest_lock, ip, 0);
          current->lockdep_recursion = 0;
          raw_local_irq_restore(flags);
  }
  EXPORT_SYMBOL_GPL(lock_acquire);
  
  void lock_release(struct lockdep_map *lock, int nested,
                            unsigned long ip)
  {
          unsigned long flags;
  
          if (unlikely(current->lockdep_recursion))
                  return;
  
          raw_local_irq_save(flags);
          check_flags(flags);
          current->lockdep_recursion = 1;
          trace_lock_release(lock, ip);
          __lock_release(lock, nested, ip);
          current->lockdep_recursion = 0;
          raw_local_irq_restore(flags);
  }
  EXPORT_SYMBOL_GPL(lock_release);
  
  int lock_is_held(struct lockdep_map *lock)
  {
          unsigned long flags;
          int ret = 0;
  
          if (unlikely(current->lockdep_recursion))
                  return 1; /* avoid false negative lockdep_assert_held() */
  
          raw_local_irq_save(flags);
          check_flags(flags);
  
          current->lockdep_recursion = 1;
          ret = __lock_is_held(lock);
          current->lockdep_recursion = 0;
          raw_local_irq_restore(flags);
  
          return ret;
  }
  EXPORT_SYMBOL_GPL(lock_is_held);
  
  void lockdep_set_current_reclaim_state(gfp_t gfp_mask)
  {
          current->lockdep_reclaim_gfp = gfp_mask;
  }
  
  void lockdep_clear_current_reclaim_state(void)
  {
          current->lockdep_reclaim_gfp = 0;
  }
  
  #ifdef CONFIG_LOCK_STAT
  static int
  print_lock_contention_bug(struct task_struct *curr, struct lockdep_map *lock,
                             unsigned long ip)
  {
          if (!debug_locks_off())
                  return 0;
          if (debug_locks_silent)
                  return 0;
  
          printk("\n");
          printk("=================================\n");
          printk("[ BUG: bad contention detected! ]\n");
          print_kernel_ident();
          printk("---------------------------------\n");
          printk("%s/%d is trying to contend lock (",
                  curr->comm, task_pid_nr(curr));
          print_lockdep_cache(lock);
          printk(") at:\n");
          print_ip_sym(ip);
          printk("but there are no locks held!\n");
          printk("\nother info that might help us debug this:\n");
          lockdep_print_held_locks(curr);
  
          printk("\nstack backtrace:\n");
          dump_stack();
  
          return 0;
  }
  
  static void
  __lock_contended(struct lockdep_map *lock, unsigned long ip)
  {
          struct task_struct *curr = current;
          struct held_lock *hlock, *prev_hlock;
          struct lock_class_stats *stats;
          unsigned int depth;
          int i, contention_point, contending_point;
  
          depth = curr->lockdep_depth;
          /*
           * Whee, we contended on this lock, except it seems we're not
           * actually trying to acquire anything much at all..
           */
          if (DEBUG_LOCKS_WARN_ON(!depth))
                  return;
  
          prev_hlock = NULL;
          for (i = depth-1; i >= 0; i--) {
                  hlock = curr->held_locks + i;
                  /*
                   * We must not cross into another context:
                   */
                  if (prev_hlock && prev_hlock->irq_context != hlock->irq_context)
                          break;
                  if (match_held_lock(hlock, lock))
                          goto found_it;
                  prev_hlock = hlock;
          }
          print_lock_contention_bug(curr, lock, ip);
          return;
  
  found_it:
          if (hlock->instance != lock)
                  return;
  
          hlock->waittime_stamp = lockstat_clock();
  
          contention_point = lock_point(hlock_class(hlock)->contention_point, ip);
          contending_point = lock_point(hlock_class(hlock)->contending_point,
                                        lock->ip);
  
          stats = get_lock_stats(hlock_class(hlock));
          if (contention_point < LOCKSTAT_POINTS)
                  stats->contention_point[contention_point]++;
          if (contending_point < LOCKSTAT_POINTS)
                  stats->contending_point[contending_point]++;
          if (lock->cpu != smp_processor_id())
                  stats->bounces[bounce_contended + !!hlock->read]++;
          put_lock_stats(stats);
  }
  
  static void
  __lock_acquired(struct lockdep_map *lock, unsigned long ip)
  {
          struct task_struct *curr = current;
          struct held_lock *hlock, *prev_hlock;
          struct lock_class_stats *stats;
          unsigned int depth;
          u64 now, waittime = 0;
          int i, cpu;
  
          depth = curr->lockdep_depth;
          /*
           * Yay, we acquired ownership of this lock we didn't try to
           * acquire, how the heck did that happen?
           */
          if (DEBUG_LOCKS_WARN_ON(!depth))
                  return;
  
          prev_hlock = NULL;
          for (i = depth-1; i >= 0; i--) {
                  hlock = curr->held_locks + i;
                  /*
                   * We must not cross into another context:
                   */
                  if (prev_hlock && prev_hlock->irq_context != hlock->irq_context)
                          break;
                  if (match_held_lock(hlock, lock))
                          goto found_it;
                  prev_hlock = hlock;
          }
          print_lock_contention_bug(curr, lock, _RET_IP_);
          return;
  
  found_it:
          if (hlock->instance != lock)
                  return;
  
          cpu = smp_processor_id();
          if (hlock->waittime_stamp) {
                  now = lockstat_clock();
                  waittime = now - hlock->waittime_stamp;
                  hlock->holdtime_stamp = now;
          }
  
          trace_lock_acquired(lock, ip);
  
          stats = get_lock_stats(hlock_class(hlock));
          if (waittime) {
                  if (hlock->read)
                          lock_time_inc(&stats->read_waittime, waittime);
                  else
                          lock_time_inc(&stats->write_waittime, waittime);
          }
          if (lock->cpu != cpu)
                  stats->bounces[bounce_acquired + !!hlock->read]++;
          put_lock_stats(stats);
  
          lock->cpu = cpu;
          lock->ip = ip;
  }
  
  void lock_contended(struct lockdep_map *lock, unsigned long ip)
  {
          unsigned long flags;
  
          if (unlikely(!lock_stat))
                  return;
  
          if (unlikely(current->lockdep_recursion))
                  return;
  
          raw_local_irq_save(flags);
          check_flags(flags);
          current->lockdep_recursion = 1;
          trace_lock_contended(lock, ip);
          __lock_contended(lock, ip);
          current->lockdep_recursion = 0;
          raw_local_irq_restore(flags);
  }
  EXPORT_SYMBOL_GPL(lock_contended);
  
  void lock_acquired(struct lockdep_map *lock, unsigned long ip)
  {
          unsigned long flags;
  
          if (unlikely(!lock_stat))
                  return;
  
          if (unlikely(current->lockdep_recursion))
                  return;
  
          raw_local_irq_save(flags);
          check_flags(flags);
          current->lockdep_recursion = 1;
          __lock_acquired(lock, ip);
          current->lockdep_recursion = 0;
          raw_local_irq_restore(flags);
  }
  EXPORT_SYMBOL_GPL(lock_acquired);
  #endif
  
  /*
   * Used by the testsuite, sanitize the validator state
   * after a simulated failure:
   */
  
  void lockdep_reset(void)
  {
          unsigned long flags;
          int i;
  
          raw_local_irq_save(flags);
          current->curr_chain_key = 0;
          current->lockdep_depth = 0;
          current->lockdep_recursion = 0;
          memset(current->held_locks, 0, MAX_LOCK_DEPTH*sizeof(struct held_lock));
          nr_hardirq_chains = 0;
          nr_softirq_chains = 0;
          nr_process_chains = 0;
          debug_locks = 1;
          for (i = 0; i < CHAINHASH_SIZE; i++)
                  INIT_LIST_HEAD(chainhash_table + i);
          raw_local_irq_restore(flags);
  }
  
  static void zap_class(struct lock_class *class)
  {
          int i;
  
          /*
           * Remove all dependencies this lock is
           * involved in:
           */
          for (i = 0; i < nr_list_entries; i++) {
                  if (list_entries[i].class == class)
                          list_del_rcu(&list_entries[i].entry);
          }
          /*
           * Unhash the class and remove it from the all_lock_classes list:
           */
          list_del_rcu(&class->hash_entry);
          list_del_rcu(&class->lock_entry);
  
          class->key = NULL;
  }
  
  static inline int within(const void *addr, void *start, unsigned long size)
  {
          return addr >= start && addr < start + size;
  }
  
  void lockdep_free_key_range(void *start, unsigned long size)
  {
          struct lock_class *class, *next;
          struct list_head *head;
          unsigned long flags;
          int i;
          int locked;
  
          raw_local_irq_save(flags);
          locked = graph_lock();
  
          /*
           * Unhash all classes that were created by this module:
           */
          for (i = 0; i < CLASSHASH_SIZE; i++) {
                  head = classhash_table + i;
                  if (list_empty(head))
                          continue;
                  list_for_each_entry_safe(class, next, head, hash_entry) {
                          if (within(class->key, start, size))
                                  zap_class(class);
                          else if (within(class->name, start, size))
                                  zap_class(class);
                  }
          }
  
          if (locked)
                  graph_unlock();
          raw_local_irq_restore(flags);
  }
  
  void lockdep_reset_lock(struct lockdep_map *lock)
  {
          struct lock_class *class, *next;
          struct list_head *head;
          unsigned long flags;
          int i, j;
          int locked;
  
          raw_local_irq_save(flags);
  
          /*
           * Remove all classes this lock might have:
           */
          for (j = 0; j < MAX_LOCKDEP_SUBCLASSES; j++) {
                  /*
                   * If the class exists we look it up and zap it:
                   */
                  class = look_up_lock_class(lock, j);
                  if (class)
                          zap_class(class);
          }
          /*
           * Debug check: in the end all mapped classes should
           * be gone.
           */
          locked = graph_lock();
          for (i = 0; i < CLASSHASH_SIZE; i++) {
                  head = classhash_table + i;
                  if (list_empty(head))
                          continue;
                  list_for_each_entry_safe(class, next, head, hash_entry) {
                          int match = 0;
  
                          for (j = 0; j < NR_LOCKDEP_CACHING_CLASSES; j++)
                                  match |= class == lock->class_cache[j];
  
                          if (unlikely(match)) {
                                  if (debug_locks_off_graph_unlock()) {
                                          /*
                                           * We all just reset everything, how did it match?
                                           */
                                          WARN_ON(1);
                                  }
                                  goto out_restore;
                          }
                  }
          }
          if (locked)
                  graph_unlock();
  
  out_restore:
          raw_local_irq_restore(flags);
  }
  
  void lockdep_init(void)
  {
          int i;
  
          /*
           * Some architectures have their own start_kernel()
           * code which calls lockdep_init(), while we also
           * call lockdep_init() from the start_kernel() itself,
           * and we want to initialize the hashes only once:
           */
          if (lockdep_initialized)
                  return;
  
          for (i = 0; i < CLASSHASH_SIZE; i++)
                  INIT_LIST_HEAD(classhash_table + i);
  
          for (i = 0; i < CHAINHASH_SIZE; i++)
                  INIT_LIST_HEAD(chainhash_table + i);
  
          lockdep_initialized = 1;
  }
  
  void __init lockdep_info(void)
  {
          printk("Lock dependency validator: Copyright (c) 2006 Red Hat, Inc., Ingo Molnar\n");
  
          printk("... MAX_LOCKDEP_SUBCLASSES:  %lu\n", MAX_LOCKDEP_SUBCLASSES);
          printk("... MAX_LOCK_DEPTH:          %lu\n", MAX_LOCK_DEPTH);
          printk("... MAX_LOCKDEP_KEYS:        %lu\n", MAX_LOCKDEP_KEYS);
          printk("... CLASSHASH_SIZE:          %lu\n", CLASSHASH_SIZE);
          printk("... MAX_LOCKDEP_ENTRIES:     %lu\n", MAX_LOCKDEP_ENTRIES);
          printk("... MAX_LOCKDEP_CHAINS:      %lu\n", MAX_LOCKDEP_CHAINS);
          printk("... CHAINHASH_SIZE:          %lu\n", CHAINHASH_SIZE);
  
          printk(" memory used by lock dependency info: %lu kB\n",
                  (sizeof(struct lock_class) * MAX_LOCKDEP_KEYS +
                  sizeof(struct list_head) * CLASSHASH_SIZE +
                  sizeof(struct lock_list) * MAX_LOCKDEP_ENTRIES +
                  sizeof(struct lock_chain) * MAX_LOCKDEP_CHAINS +
                  sizeof(struct list_head) * CHAINHASH_SIZE
  #ifdef CONFIG_PROVE_LOCKING
                  + sizeof(struct circular_queue)
  #endif
                  ) / 1024
                  );
  
          printk(" per task-struct memory footprint: %lu bytes\n",
                  sizeof(struct held_lock) * MAX_LOCK_DEPTH);
  
  #ifdef CONFIG_DEBUG_LOCKDEP
          if (lockdep_init_error) {
                  printk("WARNING: lockdep init error! lock-%s was acquired"
                          "before lockdep_init\n", lock_init_error);
                  printk("Call stack leading to lockdep invocation was:\n");
                  print_stack_trace(&lockdep_init_trace, 0);
          }
  #endif
  }
  
  static void
  print_freed_lock_bug(struct task_struct *curr, const void *mem_from,
                       const void *mem_to, struct held_lock *hlock)
  {
          if (!debug_locks_off())
                  return;
          if (debug_locks_silent)
                  return;
  
          printk("\n");
          printk("=========================\n");
          printk("[ BUG: held lock freed! ]\n");
          print_kernel_ident();
          printk("-------------------------\n");
          printk("%s/%d is freeing memory %p-%p, with a lock still held there!\n",
                  curr->comm, task_pid_nr(curr), mem_from, mem_to-1);
          print_lock(hlock);
          lockdep_print_held_locks(curr);
  
          printk("\nstack backtrace:\n");
          dump_stack();
  }
  
  static inline int not_in_range(const void* mem_from, unsigned long mem_len,
                                  const void* lock_from, unsigned long lock_len)
  {
          return lock_from + lock_len <= mem_from ||
                  mem_from + mem_len <= lock_from;
  }
  
  /*
   * Called when kernel memory is freed (or unmapped), or if a lock
   * is destroyed or reinitialized - this code checks whether there is
   * any held lock in the memory range of <from> to <to>:
   */
  void debug_check_no_locks_freed(const void *mem_from, unsigned long mem_len)
  {
          struct task_struct *curr = current;
          struct held_lock *hlock;
          unsigned long flags;
          int i;
  
          if (unlikely(!debug_locks))
                  return;
  
          local_irq_save(flags);
          for (i = 0; i < curr->lockdep_depth; i++) {
                  hlock = curr->held_locks + i;
  
                  if (not_in_range(mem_from, mem_len, hlock->instance,
                                          sizeof(*hlock->instance)))
                          continue;
  
                  print_freed_lock_bug(curr, mem_from, mem_from + mem_len, hlock);
                  break;
          }
          local_irq_restore(flags);
  }
  EXPORT_SYMBOL_GPL(debug_check_no_locks_freed);
  
  static void print_held_locks_bug(struct task_struct *curr)
  {
          if (!debug_locks_off())
                  return;
          if (debug_locks_silent)
                  return;
  
          printk("\n");
          printk("=====================================\n");
          printk("[ BUG: lock held at task exit time! ]\n");
          print_kernel_ident();
          printk("-------------------------------------\n");
          printk("%s/%d is exiting with locks still held!\n",
                  curr->comm, task_pid_nr(curr));
          lockdep_print_held_locks(curr);
  
          printk("\nstack backtrace:\n");
          dump_stack();
  }
  
  void debug_check_no_locks_held(struct task_struct *task)
  {
          if (unlikely(task->lockdep_depth > 0))
                  print_held_locks_bug(task);
  }
  
  void debug_show_all_locks(void)
  {
          struct task_struct *g, *p;
          int count = 10;
          int unlock = 1;
  
          if (unlikely(!debug_locks)) {
                  printk("INFO: lockdep is turned off.\n");
                  return;
          }
          printk("\nShowing all locks held in the system:\n");
  
          /*
           * Here we try to get the tasklist_lock as hard as possible,
           * if not successful after 2 seconds we ignore it (but keep
           * trying). This is to enable a debug printout even if a
           * tasklist_lock-holding task deadlocks or crashes.
           */
  retry:
          if (!read_trylock(&tasklist_lock)) {
                  if (count == 10)
                          printk("hm, tasklist_lock locked, retrying... ");
                  if (count) {
                          count--;
                          printk(" #%d", 10-count);
                          mdelay(200);
                          goto retry;
                  }
                  printk(" ignoring it.\n");
                  unlock = 0;
          } else {
                  if (count != 10)
                          printk(KERN_CONT " locked it.\n");
          }
  
          do_each_thread(g, p) {
                  /*
                   * It's not reliable to print a task's held locks
                   * if it's not sleeping (or if it's not the current
                   * task):
                   */
                  if (p->state == TASK_RUNNING && p != current)
                          continue;
                  if (p->lockdep_depth)
                          lockdep_print_held_locks(p);
                  if (!unlock)
                          if (read_trylock(&tasklist_lock))
                                  unlock = 1;
          } while_each_thread(g, p);
  
          printk("\n");
          printk("=============================================\n\n");
  
          if (unlock)
                  read_unlock(&tasklist_lock);
  }
  EXPORT_SYMBOL_GPL(debug_show_all_locks);
  
  /*
   * Careful: only use this function if you are sure that
   * the task cannot run in parallel!
   */
  void debug_show_held_locks(struct task_struct *task)
  {
          if (unlikely(!debug_locks)) {
                  printk("INFO: lockdep is turned off.\n");
                  return;
          }
          lockdep_print_held_locks(task);
  }
  EXPORT_SYMBOL_GPL(debug_show_held_locks);
  
  void lockdep_sys_exit(void)
  {
          struct task_struct *curr = current;
  
          if (unlikely(curr->lockdep_depth)) {
                  if (!debug_locks_off())
                          return;
                  printk("\n");
                  printk("================================================\n");
                  printk("[ BUG: lock held when returning to user space! ]\n");
                  print_kernel_ident();
                  printk("------------------------------------------------\n");
                  printk("%s/%d is leaving the kernel with locks still held!\n",
                                  curr->comm, curr->pid);
                  lockdep_print_held_locks(curr);
          }
  }
  
  void lockdep_rcu_suspicious(const char *file, const int line, const char *s)
  {
          struct task_struct *curr = current;
  
  #ifndef CONFIG_PROVE_RCU_REPEATEDLY
          if (!debug_locks_off())
                  return;
  #endif /* #ifdef CONFIG_PROVE_RCU_REPEATEDLY */
          /* Note: the following can be executed concurrently, so be careful. */
          printk("\n");
          printk("===============================\n");
          printk("[ INFO: suspicious RCU usage. ]\n");
          print_kernel_ident();
          printk("-------------------------------\n");
          printk("%s:%d %s!\n", file, line, s);
          printk("\nother info that might help us debug this:\n\n");
          printk("\n%srcu_scheduler_active = %d, debug_locks = %d\n",
                 !rcu_lockdep_current_cpu_online()
                          ? "RCU used illegally from offline CPU!\n"
                          : rcu_is_cpu_idle()
                                  ? "RCU used illegally from idle CPU!\n"
                                  : "",
                 rcu_scheduler_active, debug_locks);
  
          /*
           * If a CPU is in the RCU-free window in idle (ie: in the section
           * between rcu_idle_enter() and rcu_idle_exit(), then RCU
           * considers that CPU to be in an "extended quiescent state",
           * which means that RCU will be completely ignoring that CPU.
           * Therefore, rcu_read_lock() and friends have absolutely no
           * effect on a CPU running in that state. In other words, even if
           * such an RCU-idle CPU has called rcu_read_lock(), RCU might well
           * delete data structures out from under it.  RCU really has no
           * choice here: we need to keep an RCU-free window in idle where
           * the CPU may possibly enter into low power mode. This way we can
           * notice an extended quiescent state to other CPUs that started a grace
           * period. Otherwise we would delay any grace period as long as we run
           * in the idle task.
           *
           * So complain bitterly if someone does call rcu_read_lock(),
           * rcu_read_lock_bh() and so on from extended quiescent states.
           */
          if (rcu_is_cpu_idle())
                  printk("RCU used illegally from extended quiescent state!\n");
  
          lockdep_print_held_locks(curr);
          printk("\nstack backtrace:\n");
          dump_stack();
  }
  EXPORT_SYMBOL_GPL(lockdep_rcu_suspicious);