[PATCH] lockdep: debug_locks check after check_chain_key

In __lock_acquire check_chain_key can turn off debug_locks, so check is
needed to assure proper return code.

Signed-off-by: Jarek Poplawski <jarkao2@o2.pl>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/lockdep.c

@@ -2228,6 +2228,10 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
 
 	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");