Ming,
On 2018/02/27 17:35, Ming Lei wrote:
> On Tue, Feb 27, 2018 at 04:28:30PM -0800, Bart Van Assche wrote:
>> If a request times out the .completed_request() method is not called
>
> If BLK_EH_HANDLED is returned from .timeout(), __blk_mq_complete_request()
> should have called .completed_request(). Otherwise, somewhere may be
> wrong about timeout handling. Could you investigate why .completed_request
> isn't called under this situation?
Actually, the commit message is a little misleading. The problem is not only for
timeout but also for commands completing with a failure. This is very easy to
reproduce by simply doing an unaligned write to a sequential zone on an ATA
zoned block device. In this case, the scheduler .completed_request method is not
called, which result in the target zone of the failed write to remain locked.
Hence the addition of a .finish_request method in mq-deadline pointing to the
same function as .completed_request to ensure that the command target zone is
unlocked. To ensure that the .finish_request method is called, the RQF_ELVPRIV
flag is set when the request is dispatched after the target zone was locked.
>> and the .finish_request() method is only called if RQF_ELVPRIV has
>
> .finish_request() is counter-pair of .prepare_request(), and both
> aren't implemented by mq-deadline, so RQF_ELVPRIV needn't to be set,
> and the current rule is that this flag is managed by block core.
Indeed. So do you think it would be better to rather force a call to
.completed_request for failed command in ATA case ? Currently, it is not called
after all retries for the command failed.
>
>> been set. Hence this patch that sets RQF_ELVPRIV and that adds a
>> .finish_request() method. Without this patch, if a request times out
>> the zone that request applies to remains locked forever and no further
>> writes are accepted for that zone.
>>
>> Fixes: 5700f69178e9 ("mq-deadline: Introduce zone locking support")
>> Signed-off-by: Damien Le Moal <damien.lemoal@xxxxxxx>
>> Signed-off-by: Bart Van Assche <bart.vanassche@xxxxxxx>
>> Cc: Hannes Reinecke <hare@xxxxxxxx>
>> Cc: Ming Lei <ming.lei@xxxxxxxxxx>
>> ---
>> block/mq-deadline.c | 8 ++++++--
>> 1 file changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/block/mq-deadline.c b/block/mq-deadline.c
>> index c56f211c8440..55d5b7a02d62 100644
>> --- a/block/mq-deadline.c
>> +++ b/block/mq-deadline.c
>> @@ -367,7 +367,8 @@ static struct request *__dd_dispatch_request(struct deadline_data *dd)
>> * If the request needs its target zone locked, do it.
>> */
>> blk_req_zone_write_lock(rq);
>> - rq->rq_flags |= RQF_STARTED;
>> + /* Set RQF_ELVPRIV to ensure that .finish_request() gets called */
>> + rq->rq_flags |= RQF_STARTED | RQF_ELVPRIV;
>> return rq;
>> }
>>
>> @@ -539,7 +540,9 @@ static void dd_insert_requests(struct blk_mq_hw_ctx *hctx,
>> * For zoned block devices, write unlock the target zone of
>> * completed write requests. Do this while holding the zone lock
>> * spinlock so that the zone is never unlocked while deadline_fifo_request()
>> - * while deadline_next_request() are executing.
>> + * while deadline_next_request() are executing. This function is called twice
>> + * for requests that complete in a normal way and once for requests that time
>> + * out.
>> */
>> static void dd_completed_request(struct request *rq)
>> {
>> @@ -757,6 +760,7 @@ static struct elevator_type mq_deadline = {
>> .insert_requests = dd_insert_requests,
>> .dispatch_request = dd_dispatch_request,
>> .completed_request = dd_completed_request,
>> + .finish_request = dd_completed_request,
>> .next_request = elv_rb_latter_request,
>> .former_request = elv_rb_former_request,
>> .bio_merge = dd_bio_merge,
>> --
>> 2.16.2
>>
>
--
Damien Le Moal
Western Digital Research
