[PATCH] lockdep: improve verbose messages

Make verbose lockdep messages (off by default) more informative by printing
out the hash chain key.  (this patch was what helped me catch the earlier
lockdep hash-collision bug)
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

kernel/lockdep.c

@@ -1264,7 +1264,7 @@ register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force)
  * add it and return 0 - in this case the new dependency chain is
  * validated. If the key is already hashed, return 1.
  */
-static inline int lookup_chain_cache(u64 chain_key)
+static inline int lookup_chain_cache(u64 chain_key, struct lock_class *class)
 {
 	struct list_head *hash_head = chainhashentry(chain_key);
 	struct lock_chain *chain;
@@ -1286,9 +1286,13 @@ static inline int lookup_chain_cache(u64 chain_key)
 			__raw_spin_lock(&hash_lock);
 			return 1;
 #endif
+			if (very_verbose(class))
+				printk("\nhash chain already cached, key: %016Lx tail class: [%p] %s\n", chain_key, class->key, class->name);
 			return 0;
 		}
 	}
+	if (very_verbose(class))
+		printk("\nnew hash chain, key: %016Lx tail class: [%p] %s\n", chain_key, class->key, class->name);
 	/*
 	 * Allocate a new chain entry from the static array, and add
 	 * it to the hash:
@@ -2139,7 +2143,7 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
 	 * (If lookup_chain_cache() returns with 1 it acquires
 	 * hash_lock for us)
 	 */
-	if (!trylock && (check == 2) && lookup_chain_cache(chain_key)) {
+	if (!trylock && (check == 2) && lookup_chain_cache(chain_key, class)) {
 		/*
 		 * Check whether last held lock:
 		 *