linux-kernel - [77/80] jump_label: jump_label_inc may return before the code is patched

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Date:	Wed, 07 Dec 2011 08:07:37 -0800
From:	Greg KH <gregkh@...e.de>
To:	<linux-kernel@...r.kernel.org>, <stable@...r.kernel.org>
Cc:	<torvalds@...ux-foundation.org>, <akpm@...ux-foundation.org>,
	<alan@...rguk.ukuu.org.uk>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Jason Baron <jbaron@...hat.com>,
	Gleb Natapov <gleb@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: [77/80] jump_label: jump_label_inc may return before the code is patched

3.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Gleb Natapov <gleb@...hat.com>

commit bbbf7af4bf8fc69bc751818cf30521080fa47dcb upstream.

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: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Acked-by: Jason Baron <jbaron@...hat.com>
Signed-off-by: Gleb Natapov <gleb@...hat.com>
Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 kernel/jump_label.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -66,8 +66,9 @@ void jump_label_inc(struct jump_label_ke
 		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();
 }
 


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