/*
   * 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 void print_lockdep_off(const char *bug_msg)
  {
  	printk(KERN_DEBUG "%s
  ", bug_msg);
  	printk(KERN_DEBUG "turning off the locking correctness validator.
  ");

  #ifdef CONFIG_LOCK_STAT

  	printk(KERN_DEBUG "Please attach the output of /proc/lock_stat to the bug report
  ");

  #endif

  }

  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;

  		print_lockdep_off("BUG: MAX_STACK_TRACE_ENTRIES too low!");

  		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)
  {

  	/*
  	 * We can be called locklessly through debug_show_all_locks() so be
  	 * extra careful, the hlock might have been released and cleared.
  	 */
  	unsigned int class_idx = hlock->class_idx;
  
  	/* Don't re-read hlock->class_idx, can't use READ_ONCE() on bitfields: */
  	barrier();
  
  	if (!class_idx || (class_idx - 1) >= MAX_LOCKDEP_KEYS) {
  		printk("<RELEASED>
  ");
  		return;
  	}
  
  	print_lock_name(lock_classes + class_idx - 1);

  	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.
  ", curr->comm, task_pid_nr(curr));

  		return;
  	}
  	printk("%d lock%s held by %s/%d:
  ",

  		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
  ", 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:

   */

  #ifdef __KERNEL__

  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);

  }

  #endif

  /*

   * 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_rcu(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
  ", subclass);
  		printk(KERN_ERR
  			"turning off the locking correctness validator.
  ");
  		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 do an RCU walk of the hash, see lockdep_free_key_range().

  	 */

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

  
  	DEBUG_LOCKS_WARN_ON(!irqs_disabled());

  
  	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.
  ");
  		printk("the code is fine but needs lockdep annotation.
  ");
  		printk("turning off the locking correctness validator.
  ");
  		dump_stack();
  
  		return NULL;
  	}
  
  	key = lock->key->subkeys + subclass;
  	hash_head = classhashentry(key);

  	if (!graph_lock()) {

  		return NULL;
  	}
  	/*
  	 * We have to do the hash-walk again, to avoid races
  	 * with another CPU:
  	 */

  	list_for_each_entry_rcu(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()) {

  			return NULL;
  		}

  		print_lockdep_off("BUG: MAX_LOCKDEP_KEYS too low!");

  		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();

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

  		if (!graph_lock()) {

  			return NULL;
  		}
  	}
  out_unlock_set:
  	graph_unlock();

  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;

  		print_lockdep_off("BUG: MAX_LOCKDEP_ENTRIES too low!");

  		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;

  	/*

  	 * Both allocation and removal are done under the graph lock; but
  	 * iteration is under RCU-sched; see look_up_lock_class() and
  	 * lockdep_free_key_range().

  	 */
  	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;

  		DEBUG_LOCKS_WARN_ON(!irqs_disabled());
  
  		list_for_each_entry_rcu(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("
  -> #%u", depth);
  	print_lock_name(target->class);
  	printk(":
  ");
  	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:
    ");
  		__print_lock_name(source);
  		printk(" --> ");
  		__print_lock_name(parent);
  		printk(" --> ");
  		__print_lock_name(target);
  		printk("
  
  ");
  	}
  
  	printk(" Possible unsafe locking scenario:
  
  ");
  	printk("       CPU0                    CPU1
  ");
  	printk("       ----                    ----
  ");
  	printk("  lock(");
  	__print_lock_name(target);
  	printk(");
  ");
  	printk("                               lock(");
  	__print_lock_name(parent);
  	printk(");
  ");
  	printk("                               lock(");
  	__print_lock_name(target);
  	printk(");
  ");
  	printk("  lock(");
  	__print_lock_name(source);
  	printk(");
  ");
  	printk("
   *** DEADLOCK ***
  
  ");
  }

  /*
   * 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("
  ");
  	printk("======================================================
  ");
  	printk("[ INFO: possible circular locking dependency detected ]
  ");

  	print_kernel_ident();

  	printk("-------------------------------------------------------
  ");

  	printk("%s/%d is trying to acquire lock:
  ",

  		curr->comm, task_pid_nr(curr));

  	print_lock(check_src);

  	printk("
  but task is already holding lock:
  ");

  	print_lock(check_tgt);

  	printk("
  which lock already depends on the new lock.
  
  ");
  	printk("
  the existing dependency chain (in reverse order) is:
  ");
  
  	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("
  other info that might help us debug this:
  
  ");

  	print_circular_lock_scenario(check_src, check_tgt,
  				     first_parent);

  	lockdep_print_held_locks(curr);
  
  	printk("
  stack backtrace:
  ");
  	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
  ", ret);
  
  	return 0;
  }

  static int noop_count(struct lock_list *entry, void *data)

  {

  	(*(unsigned long *)data)++;
  	return 0;
  }

  static 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;
  }

  static 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(" {
  ");
  
  	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:
  ");
  			print_stack_trace(class->usage_traces + bit, len);
  		}
  	}
  	printk("%*s }
  ", 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:
  ", depth, "");
  		print_stack_trace(&entry->trace, 2);
  		printk("
  ");
  
  		if (depth == 0 && (entry != root)) {

  			printk("lockdep:%s bad path found in chain graph
  ", __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:
    ");
  		__print_lock_name(safe_class);
  		printk(" --> ");
  		__print_lock_name(middle_class);
  		printk(" --> ");
  		__print_lock_name(unsafe_class);
  		printk("
  
  ");
  	}
  
  	printk(" Possible interrupt unsafe locking scenario:
  
  ");
  	printk("       CPU0                    CPU1
  ");
  	printk("       ----                    ----
  ");
  	printk("  lock(");
  	__print_lock_name(unsafe_class);
  	printk(");
  ");
  	printk("                               local_irq_disable();
  ");
  	printk("                               lock(");
  	__print_lock_name(safe_class);
  	printk(");
  ");
  	printk("                               lock(");
  	__print_lock_name(middle_class);
  	printk(");
  ");
  	printk("  <Interrupt>
  ");
  	printk("    lock(");
  	__print_lock_name(safe_class);
  	printk(");
  ");
  	printk("
   *** DEADLOCK ***
  
  ");
  }

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

  		irqclass, irqclass);

  	print_kernel_ident();

  	printk("------------------------------------------------------
  ");

  	printk("%s/%d [HC%u[%lu]:SC%u[%lu]:HE%u:SE%u] is trying to acquire:
  ",

  		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("
  and this task is already holding:
  ");
  	print_lock(prev);
  	printk("which would create a new lock dependency:
  ");

  	print_lock_name(hlock_class(prev));

  	printk(" ->");

  	print_lock_name(hlock_class(next));

  	printk("
  ");
  
  	printk("
  but this new dependency connects a %s-irq-safe lock:
  ",
  		irqclass);

  	print_lock_name(backwards_entry->class);

  	printk("
  ... which became %s-irq-safe at:
  ", irqclass);

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

  
  	printk("
  to a %s-irq-unsafe lock:
  ", irqclass);

  	print_lock_name(forwards_entry->class);

  	printk("
  ... which became %s-irq-unsafe at:
  ", irqclass);
  	printk("...");

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

  
  	printk("
  other info that might help us debug this:
  
  ");

  	print_irq_lock_scenario(backwards_entry, forwards_entry,
  				hlock_class(prev), hlock_class(next));

  	lockdep_print_held_locks(curr);

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

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

  
  	printk("
  stack backtrace:
  ");
  	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:
  
  ");
  	printk("       CPU0
  ");
  	printk("       ----
  ");
  	printk("  lock(");
  	__print_lock_name(prev);
  	printk(");
  ");
  	printk("  lock(");
  	__print_lock_name(next);
  	printk(");
  ");
  	printk("
   *** DEADLOCK ***
  
  ");
  	printk(" May be due to missing lock nesting notation
  
  ");
  }

  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("
  ");
  	printk("=============================================
  ");
  	printk("[ INFO: possible recursive locking detected ]
  ");

  	print_kernel_ident();

  	printk("---------------------------------------------
  ");

  	printk("%s/%d is trying to acquire lock:
  ",

  		curr->comm, task_pid_nr(curr));

  	print_lock(next);
  	printk("
  but task is already holding lock:
  ");
  	print_lock(prev);
  
  	printk("
  other info that might help us debug this:
  ");

  	print_deadlock_scenario(next, prev);

  	lockdep_print_held_locks(curr);
  
  	printk("
  stack backtrace:
  ");
  	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("
   new dependency: ");

  		print_lock_name(hlock_class(prev));

  		printk(" => ");

  		print_lock_name(hlock_class(next));

  		printk("
  ");

  		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 && hlock->check) {

  			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;