Re: [patch]blk-mq: blk_mq_tag_to_rq should handle flush request

Ming Lei
2014-06-04T16:00:24Z

On Wed, Jun 4, 2014 at 11:48 PM, Jens Axboe <axboe@kernel.dk> wrote:
> On 06/04/2014 09:43 AM, Ming Lei wrote:
>> On Wed, Jun 4, 2014 at 11:31 PM, Christoph Hellwig <hch@infradead.org> wrote:
>>> On Wed, Jun 04, 2014 at 09:02:19AM -0600, Jens Axboe wrote:
>>>>> scsi_mq_find_tag only gets the scsi host, which may have multiple
>>>>> queues. When called from scsi_find_tag we actually have a scsi device,
>>>>> so that's not an issue, but when called from scsi_host_find_tag the
>>>>> driver only provides the host.
>>>>
>>>> Only solution I see right now is to have the flush_rq in the shared
>>>> tags, but that would potentially be a regression for multiple
>>>> devices and heavy flush uses cases. I'll see if I can come up with
>>>> something better, or maybe Shaohua has an idea.
>>>
>>> What about something like the following (untest, uncompiled, maybe
>>> pseudo-code):
>>>
>>> struct request *blk_mq_tag_to_rq(struct blk_mq_tags *tags, unsigned int tag)
>>> {
>>> struct request *rq = tags->rqs[tag];
>>>
>>> if ((rq->cmd_flags & REQ_FLUSH_SEQ) && rq->q->flush_rq->tag == tag)
>>> return rq->q->flush_rq;
>>> return rq;
>>> }
>>
>> Looks we thought it together, :-)
>>
>> Also maybe the flush_rq->tag need to be cleared in flush_end_io().
>
> It clears the command flag, so that should be enough.

Only the flush_rq's command flag is cleared, and its parent request
flag isn't cleared.

Thanks,
--
Ming Lei