Re: [PATCH] blk-mq: fix blk_mq_tagset_busy_iter

[Jens Axboe]

On 8/2/18 11:06 AM, Ming Lei wrote:
> On Thu, Aug 02, 2018 at 09:54:06AM -0700, James Bottomley wrote:
>> On Fri, 2018-08-03 at 00:43 +0800, Ming Lei wrote:
>>> Commit d250bf4e776ff09d5("blk-mq: only iterate over inflight requests
>>> in blk_mq_tagset_busy_iter") uses 'blk_mq_rq_state(rq) ==
>>> MQ_RQ_IN_FLIGHT'
>>> to replace 'blk_mq_request_started(req)', this way is wrong, and
>>> causes
>>> lots of test system hang during booting.
>>>
>>> Fix the issue by using blk_mq_request_started(req) inside
>>> bt_tags_iter().
>>>
>>> Fixes: d250bf4e776ff09d5 ("blk-mq: only iterate over inflight
>>> requests in blk_mq_tagset_busy_iter")
>>> Cc: Josef Bacik <josef@xxxxxxxxxxxxxx>
>>> Cc: Christoph Hellwig <hch@xxxxxx>
>>> Cc: Guenter Roeck <linux@xxxxxxxxxxxx>
>>> Cc: Mark Brown <broonie@xxxxxxxxxx>
>>> Cc: Matt Hart <matthew.hart@xxxxxxxxxx>
>>> Cc: Johannes Thumshirn <jthumshirn@xxxxxxx>
>>> Cc: John Garry <john.garry@xxxxxxxxxx>
>>> Cc: Hannes Reinecke <hare@xxxxxxxx>,
>>> Cc: "Martin K. Petersen" <martin.petersen@xxxxxxxxxx>,
>>> Cc: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
>>> Cc: linux-scsi@xxxxxxxxxxxxxxx
>>> Cc: linux-kernel@xxxxxxxxxxxxxxx
>>> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
>>> ---
>>> Âblock/blk-mq-tag.c | 2 +-
>>> Â1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
>>> index 09b2ee6694fb..3de0836163c2 100644
>>> --- a/block/blk-mq-tag.c
>>> +++ b/block/blk-mq-tag.c
>>> @@ -271,7 +271,7 @@ static bool bt_tags_iter(struct sbitmap *bitmap,
>>> unsigned int bitnr, void *data)
>>> Â	Â* test and set the bit before assining ->rqs[].
>>> Â	Â*/
>>> Â	rq = tags->rqs[bitnr];
>>> -	if (rq && blk_mq_rq_state(rq) == MQ_RQ_IN_FLIGHT)
>>> +	if (rq && blk_mq_request_started(rq))
>>
>> So now we have dueling versions of this patch:
>>
>> https://marc.info/?l=linux-scsi&m=153322802207688
>>
>> Can we at least make sure we've root caused the problem and confirmed
>> we've got it fixed before we start the formal patch process?  When we
> 
> EH uses scsi_host_busy to check if the error handler needs to be waken
> up. And blk_mq_tagset_busy_iter() is used for implementing scsi_host_busy(),
> so causes EH not waken up, then this timed-out request can't be handled.
> 
>> do start the formal patch process, please give appropriate credit to
>> the reporter(s) since this has been a royal pain for them to help us
>> track down.
> 
> Sure.
> 
> Jens, could you add reported-by if you are fine with this version? Or please
> just let me know if new version is needed, then I can add it.

I'll add that, would also love a tested-by from the reporter. The patch
looks good to me, however.

-- 
Jens Axboe