[tip:perf/core] jump_label: jump_label_inc may return before the code is patched

[tip-bot for Gleb Natapov <gleb@redhat.com>]

Commit-ID:  bbbf7af4bf8fc69bc751818cf30521080fa47dcb
Gitweb:     http://git.kernel.org/tip/bbbf7af4bf8fc69bc751818cf30521080fa47dcb
Author:     Gleb Natapov <gleb@redhat.com>
AuthorDate: Tue, 18 Oct 2011 19:55:51 +0200
Committer:  Steven Rostedt <rostedt@goodmis.org>
CommitDate: Mon, 5 Dec 2011 13:28:46 -0500

jump_label: jump_label_inc may return before the code is patched

If cpu A calls jump_label_inc() just after atomic_add_return() is
called by cpu B, atomic_inc_not_zero() will return value greater then
zero and jump_label_inc() will return to a caller before jump_label_update()
finishes its job on cpu B.

Link: http://lkml.kernel.org/r/20111018175551.GH17571@redhat.com

Cc: stable@vger.kernel.org
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Jason Baron <jbaron@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 kernel/jump_label.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index bbdfe2a..66ff710 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -66,8 +66,9 @@ void jump_label_inc(struct jump_label_key *key)
 		return;
 
 	jump_label_lock();
-	if (atomic_add_return(1, &key->enabled) == 1)
+	if (atomic_read(&key->enabled) == 0)
 		jump_label_update(key, JUMP_LABEL_ENABLE);
+	atomic_inc(&key->enabled);
 	jump_label_unlock();
 }