On 04/28/2017 09:59 AM, Bart Van Assche wrote: > On Fri, 2017-04-28 at 07:42 -0600, Jens Axboe wrote: >> On 04/28/2017 01:32 AM, Ming Lei wrote: >>> We have freezed queue already, not necessary to call >>> blk_mq_quiesce_queue() any more, so remove it. >> >> Are you sure? It ensures that we also aren't in the middle of >> blk_mq_make_request(), we need a stable view of the sched >> status throughout that. > > Hello Jens, > > My understanding is that blk_mq_freeze_queue() provides stronger > guarantees than blk_mq_quiesce_queue(). The former waits until all > pending requests have finished while the latter only waits until > pending .queue_rq() calls have finished. blk_mq_freeze_queue() also > causes new blk_get_request() calls to wait until > blk_mq_unfreeze_queue() is called while blk_get_request() can still > succeed after blk_mq_quiesce_queue() returned and before > blk_mq_start_stopped_hw_queues() is called. > > Regarding blk_mq_make_request(): I think that the blk_queue_enter() > call in generic_make_request() prevents that blk_mq_make_request() > gets called after a queue has been frozen. Bart, you are right, I'm fine with the patch. -- Jens Axboe
