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.