lockdep: fix mismatched lockdep_depth/curr_chain_hash

patch 3aa416b0 in mainline.

lockdep: fix mismatched lockdep_depth/curr_chain_hash

It is possible for the current->curr_chain_key to become inconsistent with the
current index if the chain fails to validate.  The end result is that future
lock_acquire() operations may inadvertently fail to find a hit in the cache
resulting in a new node being added to the graph for every acquire.

[ peterz: this might explain some of the lockdep is so _slow_ complaints. ]
[ mingo: this does not impact the correctness of validation, but may slow
  down future operations significantly, if the chain gets very long. ]
Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

kernel/lockdep.c

@@ -2166,7 +2166,6 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
 	}
 #endif
 	chain_key = iterate_chain_key(chain_key, id);
-	curr->curr_chain_key = chain_key;
 
 	/*
 	 * Trylock needs to maintain the stack of held locks, but it
@@ -2215,6 +2214,7 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
 		if (unlikely(!debug_locks))
 			return 0;
 
+	curr->curr_chain_key = chain_key;
 	curr->lockdep_depth++;
 	check_chain_key(curr);
 #ifdef CONFIG_DEBUG_LOCKDEP