linux-kernel - Re: [PATCH V2 8/8] blk-mq: remove blk_mq_tagset_busy

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Date:   Mon, 25 Mar 2019 15:37:04 +0800
From:   "jianchao.wang" <jianchao.w.wang@...cle.com>
To:     Hannes Reinecke <hare@...e.de>, axboe@...nel.dk
Cc:     linux-block@...r.kernel.org, jsmart2021@...il.com,
        sagi@...mberg.me, josef@...icpanda.com,
        linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
        keith.busch@...el.com, jthumshirn@...e.de, hch@....de,
        bvanassche@....org
Subject: Re: [PATCH V2 8/8] blk-mq: remove blk_mq_tagset_busy_iter

Hi Hannes

On 3/25/19 3:18 PM, Hannes Reinecke wrote:
> On 3/25/19 6:38 AM, Jianchao Wang wrote:
>> As nobody uses blk_mq_tagset_busy_iter, remove it.
>>
>> Signed-off-by: Jianchao Wang <jianchao.w.wang@...cle.com>
>> ---
>>   block/blk-mq-tag.c     | 95 --------------------------------------------------
>>   include/linux/blk-mq.h |  2 --
>>   2 files changed, 97 deletions(-)
>>
> Please, don't.
> 
> I'm currently implementing reserved commands for SCSI and reworking the SCSI error handling where I rely on this interface quite heavily.

blk_mq_tagset_busy_iter could access some stale requests which maybe freed due to io scheduler switching, request_queue cleanup (shared tagset)
when there is someone submits io and gets driver tag. When io scheduler attached, even quiesce request_queue won't work.

If this patchset is accepted, blk_mq_tagset_busy_iter could be replaced with blk_mq_queue_inflight_tag_iter which needs
to be invoked by every request_queue that shares the tagset.

Please go ahead your work.

Thanks
Jianchao

> 
> Cheers,
> 
> Hannes