From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752760AbbBRRGG (ORCPT ); Wed, 18 Feb 2015 12:06:06 -0500 Received: from terminus.zytor.com ([198.137.202.10]:38899 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752054AbbBRRGA (ORCPT ); Wed, 18 Feb 2015 12:06:00 -0500 Date: Wed, 18 Feb 2015 09:05:15 -0800 From: tip-bot for Sebastian Andrzej Siewior Message-ID: Cc: peterz@infradead.org, bigeasy@linutronix.de, mingo@kernel.org, hpa@zytor.com, tglx@linutronix.de, linux-kernel@vger.kernel.org Reply-To: bigeasy@linutronix.de, peterz@infradead.org, tglx@linutronix.de, linux-kernel@vger.kernel.org, mingo@kernel.org, hpa@zytor.com In-Reply-To: <1424187823-19600-1-git-send-email-bigeasy@linutronix.de> References: <1424187823-19600-1-git-send-email-bigeasy@linutronix.de> To: linux-tip-commits@vger.kernel.org Subject: [tip:locking/core] locking/rtmutex: Avoid a NULL pointer dereference on deadlock Git-Commit-ID: 8d1e5a1a1ccf5ae9d8a5a0ee7960202ccb0c5429 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 8d1e5a1a1ccf5ae9d8a5a0ee7960202ccb0c5429 Gitweb: http://git.kernel.org/tip/8d1e5a1a1ccf5ae9d8a5a0ee7960202ccb0c5429 Author: Sebastian Andrzej Siewior AuthorDate: Tue, 17 Feb 2015 16:43:43 +0100 Committer: Ingo Molnar CommitDate: Wed, 18 Feb 2015 10:20:32 +0100 locking/rtmutex: Avoid a NULL pointer dereference on deadlock With task_blocks_on_rt_mutex() returning early -EDEADLK we never add the waiter to the waitqueue. Later, we try to remove it via remove_waiter() and go boom in rt_mutex_top_waiter() because rb_entry() gives a NULL pointer. ( Tested on v3.18-RT where rtmutex is used for regular mutex and I tried to get one twice in a row. ) Not sure when this started but I guess 397335f004f4 ("rtmutex: Fix deadlock detector for real") or commit 3d5c9340d194 ("rtmutex: Handle deadlock detection smarter"). Signed-off-by: Sebastian Andrzej Siewior Acked-by: Peter Zijlstra Cc: Thomas Gleixner Cc: # for v3.16 and later kernels Link: http://lkml.kernel.org/r/1424187823-19600-1-git-send-email-bigeasy@linutronix.de Signed-off-by: Ingo Molnar --- kernel/locking/rtmutex.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c index 3059bc2f..e16e554 100644 --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -1193,7 +1193,8 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state, ret = __rt_mutex_slowlock(lock, state, timeout, &waiter); if (unlikely(ret)) { - remove_waiter(lock, &waiter); + if (rt_mutex_has_waiters(lock)) + remove_waiter(lock, &waiter); rt_mutex_handle_deadlock(ret, chwalk, &waiter); }