linux-kernel - Re: [PATCH] blk-mq: fix blk_mq_tagset_busy

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Date:   Thu, 2 Aug 2018 11:08:22 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Ming Lei <ming.lei@...hat.com>,
        James Bottomley <James.Bottomley@...senPartnership.com>
Cc:     linux-block@...r.kernel.org, Josef Bacik <josef@...icpanda.com>,
        Christoph Hellwig <hch@....de>,
        Guenter Roeck <linux@...ck-us.net>,
        Mark Brown <broonie@...nel.org>,
        Matt Hart <matthew.hart@...aro.org>,
        Johannes Thumshirn <jthumshirn@...e.de>,
        John Garry <john.garry@...wei.com>,
        Hannes Reinecke <hare@...e.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] blk-mq: fix blk_mq_tagset_busy_iter

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@...icpanda.com>
>>> Cc: Christoph Hellwig <hch@....de>
>>> Cc: Guenter Roeck <linux@...ck-us.net>
>>> Cc: Mark Brown <broonie@...nel.org>
>>> Cc: Matt Hart <matthew.hart@...aro.org>
>>> Cc: Johannes Thumshirn <jthumshirn@...e.de>
>>> Cc: John Garry <john.garry@...wei.com>
>>> Cc: Hannes Reinecke <hare@...e.com>,
>>> Cc: "Martin K. Petersen" <martin.petersen@...cle.com>,
>>> Cc: James Bottomley <James.Bottomley@...senpartnership.com>
>>> Cc: linux-scsi@...r.kernel.org
>>> Cc: linux-kernel@...r.kernel.org
>>> Signed-off-by: Ming Lei <ming.lei@...hat.com>
>>> ---
>>>  block/blk-mq-tag.c | 2 +-
>>>  1 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)
>>>  	 * test and set the bit before assining ->rqs[].
>>>  	 */
>>>  	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