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>

diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index bbdfe2a..66ff710 100644 (file)
--- 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();
 }