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 <peterz@xxxxxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx # 3.15 Signed-off-by: Ilya Dryomov <ilya.dryomov@xxxxxxxxxxx> --- 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 ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
