[PATCH 7/7] lockdep: Remove cmpxchg to update nr_chain_hlocks

[Steven Rostedt <rostedt@goodmis.org>]

[-- Attachment #1: 0007-lockdep-Remove-cmpxchg-to-update-nr_chain_hlocks.patch --]
[-- Type: text/plain, Size: 1602 bytes --]

From: Steven Rostedt <srostedt@redhat.com>

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.

Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 kernel/lockdep.c |   14 ++++----------
 1 files changed, 4 insertions(+), 10 deletions(-)

diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index 3b1ac92..60bce52 100644
--- a/kernel/lockdep.c
+++ b/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 @@ 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;
-- 
1.7.2.3