On 2020-08-25 02:11, Stanley Chu wrote: >> diff --git a/block/blk-pm.c b/block/blk-pm.c >> index b85234d758f7..17bd020268d4 100644 >> --- a/block/blk-pm.c >> +++ b/block/blk-pm.c >> @@ -67,6 +67,10 @@ int blk_pre_runtime_suspend(struct request_queue *q) >> >> WARN_ON_ONCE(q->rpm_status != RPM_ACTIVE); >> >> + spin_lock_irq(&q->queue_lock); >> + q->rpm_status = RPM_SUSPENDING; >> + spin_unlock_irq(&q->queue_lock); >> + > > Has below alternative way been considered that RPM_SUSPENDING is set > after blk_freeze_queue_start()? > > blk_freeze_queue_start(q); > > + spin_lock_irq(&q->queue_lock); > + q->rpm_status = RPM_SUSPENDING; > + spin_unlock_irq(&q->queue_lock); > > > Otherwise requests can enter queue while rpm_status is RPM_SUSPENDING > during a small window, i.e., before blk_set_pm_only() is invoked. This > would make the definition of rpm_status ambiguous. > > In this way, the racing could be also solved: > > - Before blk_freeze_queue_start(), any requests shall be allowed to > enter queue > - blk_freeze_queue_start() freezes the queue and blocks all upcoming > requests (make them wait_event(q->mq_freeze_wq)) > - rpm_status is set as RPM_SUSPENDING > - blk_mq_unfreeze_queue() wakes up q->mq_freeze_wq and then > blk_pm_request_resume() can be executed Hi Stanley, I prefer the order from the patch. I think it is important to change q->rpm_status into RPM_SUSPENDING before blk_queue_enter() calls blk_queue_pm_only(). Otherwise it could happen that blk_queue_enter() calls blk_pm_request_resume() while q->rpm_status == RPM_ACTIVE, resulting in blk_queue_enter() not resuming a queue although that queue should be resumed. Thanks, Bart.
