From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754099AbbCFKTv (ORCPT ); Fri, 6 Mar 2015 05:19:51 -0500 Received: from youngberry.canonical.com ([91.189.89.112]:44673 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755274AbbCFKAk (ORCPT ); Fri, 6 Mar 2015 05:00:40 -0500 From: Luis Henriques To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Sebastian Andrzej Siewior , Thomas Gleixner , Ingo Molnar , Luis Henriques Subject: [PATCH 3.16.y-ckt 131/183] locking/rtmutex: Avoid a NULL pointer dereference on deadlock Date: Fri, 6 Mar 2015 09:57:02 +0000 Message-Id: <1425635874-19087-132-git-send-email-luis.henriques@canonical.com> X-Mailer: git-send-email 2.1.4 In-Reply-To: <1425635874-19087-1-git-send-email-luis.henriques@canonical.com> References: <1425635874-19087-1-git-send-email-luis.henriques@canonical.com> X-Extended-Stable: 3.16 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.16.7-ckt8 -stable review patch. If anyone has any objections, please let me know. ------------------ From: Sebastian Andrzej Siewior commit 8d1e5a1a1ccf5ae9d8a5a0ee7960202ccb0c5429 upstream. 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 Link: http://lkml.kernel.org/r/1424187823-19600-1-git-send-email-bigeasy@linutronix.de Signed-off-by: Ingo Molnar [ luis: backported to 3.16: adjusted context ] Signed-off-by: Luis Henriques --- 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 fc605941b9b8..f9878d16b80b 100644 --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -936,7 +936,8 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state, set_current_state(TASK_RUNNING); if (unlikely(ret)) { - remove_waiter(lock, &waiter); + if (rt_mutex_has_waiters(lock)) + remove_waiter(lock, &waiter); rt_mutex_handle_deadlock(ret, detect_deadlock, &waiter); }