lockdep

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

	if (unlikely(!debug_locks))
		return 0;

	if (!prove_locking || lock->key == &__lockdep_no_validate__)
		check = 0;

	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;
	}

	debug_class_ops_inc(class);

	if (very_verbose(class)) {
		printk("\nacquire class [%px] %s", class->key, class->name);
		if (class->name_version > 1)
			printk(KERN_CONT "#%d", class->name_version);
		printk(KERN_CONT "\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;

	if (depth && !sync) {
		/* we're holding locks and the new held lock is not a sync */
		hlock = curr->held_locks + depth - 1;
		if (hlock->class_idx == class_idx && nest_lock) {
			if (!references)
				references++;

			if (!hlock->references)
				hlock->references++;

			hlock->references += references;

			/* Overflow */
			if (DEBUG_LOCKS_WARN_ON(hlock->references < references))
				return 0;

			return 2;
		}
	}

	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->irq_context = task_irq_context(curr);
	hlock->trylock = trylock;
	hlock->read = read;
	hlock->check = check;
	hlock->sync = !!sync;
	hlock->hardirqs_off = !!hardirqs_off;
	hlock->references = references;
#ifdef CONFIG_LOCK_STAT
	hlock->waittime_stamp = 0;
	hlock->holdtime_stamp = lockstat_clock();
#endif
	hlock->pin_count = pin_count;

	if (check_wait_context(curr, hlock))
		return 0;

	/* Initialize the lock usage bit */
	if (!mark_usage(curr, hlock, check))
		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.
	 */
	/*
	 * Whoops, we did it again.. class_idx is invalid.
	 */
	if (DEBUG_LOCKS_WARN_ON(!test_bit(class_idx, lock_classes_in_use)))
		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 != INITIAL_CHAIN_KEY))
			return 0;
		chain_head = 1;
	}

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

	if (nest_lock && !__lock_is_held(nest_lock, -1)) {
		print_lock_nested_lock_not_held(curr, hlock);
		return 0;
	}

	if (!debug_locks_silent) {
		WARN_ON_ONCE(depth && !hlock_class(hlock - 1)->key);
		WARN_ON_ONCE(!hlock_class(hlock)->key);
	}

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

	/* For lock_sync(), we are done here since no actual critical section */
	if (hlock->sync)
		return 1;

	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();
		print_lockdep_off("BUG: MAX_LOCK_DEPTH too low!");
		printk(KERN_DEBUG "depth: %i  max: %lu!\n",
		       curr->lockdep_depth, MAX_LOCK_DEPTH);

		lockdep_print_held_locks(current);
		debug_show_all_locks();
		dump_stack();

		return 0;
	}

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

	return 1;
}