lockdep: Remove cmpxchg to update nr_chain_hlocks

For some reason nr_chain_hlocks is updated with cmpxchg, but
this is performed inside of the lockdep global "grab_lock()",
which also makes simple modification of this variable atomic.

Remove the cmpxchg logic for updating nr_chain_hlocks and
simplify the code.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20110421014300.727863282@goodmis.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/lockdep.c

@@ -1973,7 +1973,7 @@ static inline int lookup_chain_cache(struct task_struct *curr,
 	struct list_head *hash_head = chainhashentry(chain_key);
 	struct lock_chain *chain;
 	struct held_lock *hlock_curr, *hlock_next;
-	int i, j, n, cn;
+	int i, j;
 
 	if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
 		return 0;
@@ -2033,15 +2033,9 @@ static inline int lookup_chain_cache(struct task_struct *curr,
 	}
 	i++;
 	chain->depth = curr->lockdep_depth + 1 - i;
-	cn = nr_chain_hlocks;
-	while (cn + chain->depth <= MAX_LOCKDEP_CHAIN_HLOCKS) {
-		n = cmpxchg(&nr_chain_hlocks, cn, cn + chain->depth);
-		if (n == cn)
-			break;
-		cn = n;
-	}
-	if (likely(cn + chain->depth <= MAX_LOCKDEP_CHAIN_HLOCKS)) {
-		chain->base = cn;
+	if (likely(nr_chain_hlocks + chain->depth <= MAX_LOCKDEP_CHAIN_HLOCKS)) {
+		chain->base = nr_chain_hlocks;
+		nr_chain_hlocks += chain->depth;
 		for (j = 0; j < chain->depth - 1; j++, i++) {
 			int lock_id = curr->held_locks[i].class_idx - 1;
 			chain_hlocks[chain->base + j] = lock_id;