On Thu, Apr 4, 2019 at 11:57 PM Bart Van Assche <bvanassche@xxxxxxx> wrote:
>
> On Thu, 2019-04-04 at 16:43 +0800, Ming Lei wrote:
> > diff --git a/block/blk-mq.c b/block/blk-mq.c
> > index b512ba0cb359..41c12d9008b7 100644
> > --- a/block/blk-mq.c
> > +++ b/block/blk-mq.c
> > @@ -3224,8 +3224,11 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set,
> > if (nr_hw_queues < 1 || nr_hw_queues == set->nr_hw_queues)
> > return;
> >
> > - list_for_each_entry(q, &set->tag_list, tag_set_list)
> > + list_for_each_entry(q, &set->tag_list, tag_set_list) {
> > blk_mq_freeze_queue(q);
> > + blk_mq_quiesce_queue(q);
> > + blk_sync_queue(q);
> > + }
> > /*
> > * Sync with blk_mq_queue_tag_busy_iter.
> > */
> > @@ -3269,8 +3272,10 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set,
> > list_for_each_entry(q, &set->tag_list, tag_set_list)
> > blk_mq_elv_switch_back(&head, q);
> >
> > - list_for_each_entry(q, &set->tag_list, tag_set_list)
> > + list_for_each_entry(q, &set->tag_list, tag_set_list) {
> > + blk_mq_unquiesce_queue(q);
> > blk_mq_unfreeze_queue(q);
> > + }
> > }
> >
> > void blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, int nr_hw_queues)
>
> Are you sure this patch is sufficient? What prevents that blk_mq_run_hw_queues()
> gets called after the blk_mq_quiesce() and blk_sync_queue() calls have finished
> and before the queue is unfrozen?
blk_queue_quiesced(hctx->queue) is supposed to prevents blk_mq_run_hw_queues()
from being called after the queue is quiesced.
But there is another bug in blk_mq_quiesce() which shouldn't depend on
hctx_lock(hctx, &srcu_idx)
for this check, will fix blk_mq_quiesce() in V5.
Thanks,
Ming Lei
