lockdep: Remove cmpxchg to update nr_chain_hlocks
Steven Rostedt [Thu, 21 Apr 2011 01:42:00 +0000 (21:42 -0400)]
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

index 27c609f..63437d0 100644 (file)
@@ -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 @@ cache_hit:
        }
        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;