Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756328AbaGaKQp (ORCPT ); Thu, 31 Jul 2014 06:16:45 -0400 Received: from mail-la0-f47.google.com ([209.85.215.47]:41793 "EHLO mail-la0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756300AbaGaKQm (ORCPT ); Thu, 31 Jul 2014 06:16:42 -0400 From: Ilya Dryomov To: linux-kernel@vger.kernel.org Cc: Peter Zijlstra , Ingo Molnar , ceph-devel@vger.kernel.org Subject: [PATCH] locking/mutexes: Revert "locking/mutexes: Add extra reschedule point" Date: Thu, 31 Jul 2014 14:16:37 +0400 Message-Id: <1406801797-20139-1-git-send-email-ilya.dryomov@inktank.com> X-Mailer: git-send-email 1.7.10.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This reverts commit 34c6bc2c919a55e5ad4e698510a2f35ee13ab900. This commit can lead to deadlocks by way of what at a high level appears to look like a missing wakeup on mutex_unlock() when CONFIG_MUTEX_SPIN_ON_OWNER is set, which is how most distributions ship their kernels. In particular, it causes reproducible deadlocks in libceph/rbd code under higher than moderate loads with the evidence actually pointing to the bowels of mutex_lock(). kernel/locking/mutex.c, __mutex_lock_common(): 476 osq_unlock(&lock->osq); 477 slowpath: 478 /* 479 * If we fell out of the spin path because of need_resched(), 480 * reschedule now, before we try-lock the mutex. This avoids getting 481 * scheduled out right after we obtained the mutex. 482 */ 483 if (need_resched()) 484 schedule_preempt_disabled(); <-- never returns 485 #endif 486 spin_lock_mutex(&lock->wait_lock, flags); We started bumping into deadlocks in QA the day our branch has been rebased onto 3.15 (the release this commit went in) but then as part of debugging effort I enabled all locking debug options, which also disabled CONFIG_MUTEX_SPIN_ON_OWNER and made everything disappear, which is why it hasn't been looked into until now. Revert makes the problem go away, confirmed by our users. Cc: Peter Zijlstra Cc: stable@vger.kernel.org # 3.15 Signed-off-by: Ilya Dryomov --- kernel/locking/mutex.c | 7 ------- 1 file changed, 7 deletions(-) diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c index acca2c1a3c5e..746ff280a2fc 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -475,13 +475,6 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, } osq_unlock(&lock->osq); slowpath: - /* - * If we fell out of the spin path because of need_resched(), - * reschedule now, before we try-lock the mutex. This avoids getting - * scheduled out right after we obtained the mutex. - */ - if (need_resched()) - schedule_preempt_disabled(); #endif spin_lock_mutex(&lock->wait_lock, flags); -- 1.7.10.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/