Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S936045AbcLMRQW (ORCPT ); Tue, 13 Dec 2016 12:16:22 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:56924 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935896AbcLMRQK (ORCPT ); Tue, 13 Dec 2016 12:16:10 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Will Deacon , Thomas Gleixner , "Peter Zijlstra (Intel)" , David Daney , Linus Torvalds , Mark Rutland , Sebastian Siewior , Steven Rostedt , Ingo Molnar Subject: [PATCH 4.4 07/16] locking/rtmutex: Use READ_ONCE() in rt_mutex_owner() Date: Tue, 13 Dec 2016 09:15:53 -0800 Message-Id: <20161213171519.295490977@linuxfoundation.org> X-Mailer: git-send-email 2.10.2 In-Reply-To: <20161213171518.862135257@linuxfoundation.org> References: <20161213171518.862135257@linuxfoundation.org> User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1711 Lines: 49 4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Thomas Gleixner commit 1be5d4fa0af34fb7bafa205aeb59f5c7cc7a089d upstream. While debugging the rtmutex unlock vs. dequeue race Will suggested to use READ_ONCE() in rt_mutex_owner() as it might race against the cmpxchg_release() in unlock_rt_mutex_safe(). Will: "It's a minor thing which will most likely not matter in practice" Careful search did not unearth an actual problem in todays code, but it's better to be safe than surprised. Suggested-by: Will Deacon Signed-off-by: Thomas Gleixner Acked-by: Peter Zijlstra (Intel) Cc: David Daney Cc: Linus Torvalds Cc: Mark Rutland Cc: Peter Zijlstra Cc: Sebastian Siewior Cc: Steven Rostedt Link: http://lkml.kernel.org/r/20161130210030.431379999@linutronix.de Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman --- kernel/locking/rtmutex_common.h | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) --- a/kernel/locking/rtmutex_common.h +++ b/kernel/locking/rtmutex_common.h @@ -75,8 +75,9 @@ task_top_pi_waiter(struct task_struct *p static inline struct task_struct *rt_mutex_owner(struct rt_mutex *lock) { - return (struct task_struct *) - ((unsigned long)lock->owner & ~RT_MUTEX_OWNER_MASKALL); + unsigned long owner = (unsigned long) READ_ONCE(lock->owner); + + return (struct task_struct *) (owner & ~RT_MUTEX_OWNER_MASKALL); } /*