On Wed, May 16, 2018 at 4:56 PM, Bart Van Assche <Bart.VanAssche@xxxxxxx> wrote: > On Wed, 2018-05-16 at 22:05 +0900, Tetsuo Handa wrote: >> One ore more threads are waiting for q->mq_freeze_depth to become 0. But the >> thread who incremented q->mq_freeze_depth at blk_freeze_queue_start(q) from >> blk_freeze_queue() is waiting at blk_mq_freeze_queue_wait(). Therefore, >> atomic_read(&q->mq_freeze_depth) == 0 condition for wait_event() in >> blk_queue_enter() will never be satisfied. But what does that wait_event() >> want to do? Isn't "start freezing" a sort of blk_queue_dying(q) == true? >> Since percpu_ref_tryget_live(&q->q_usage_counter) failed and the queue is >> about to be frozen, shouldn't we treat atomic_read(&q->mq_freeze_depth) != 0 >> as if blk_queue_dying(q) == true? That is, something like below: >> >> diff --git a/block/blk-core.c b/block/blk-core.c >> index 85909b4..59e2496 100644 >> --- a/block/blk-core.c >> +++ b/block/blk-core.c >> @@ -951,10 +951,10 @@ int blk_queue_enter(struct request_queue *q, blk_mq_req_flags_t flags) >> smp_rmb(); >> >> wait_event(q->mq_freeze_wq, >> - (atomic_read(&q->mq_freeze_depth) == 0 && >> - (preempt || !blk_queue_preempt_only(q))) || >> + atomic_read(&q->mq_freeze_depth) || >> + (preempt || !blk_queue_preempt_only(q)) || >> blk_queue_dying(q)); >> - if (blk_queue_dying(q)) >> + if (atomic_read(&q->mq_freeze_depth) || blk_queue_dying(q)) >> return -ENODEV; >> } >> } > > That change looks wrong to me. Hi Bart, Why does it look wrong to you? > Additionally, I think that you are looking in > the wrong direction. Since blk_mq_freeze_queue_wait() and blk_queue_enter() > work fine for all block drivers except the loop driver I think that you should > have a closer look at how the loop driver uses this block layer functionality. > > Thanks, > > Bart. > > >
