Subject: Re: [PATCH 4/5] block: move queue enter logic into
 blk_mq_submit_bio()
To:     Geert Uytterhoeven <geert@linux-m68k.org>,
        Ming Lei <ming.lei@redhat.com>
References: <461c4758-2675-1d11-ac8a-6f25ef01d781@kernel.dk>
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Cc:     Jens Axboe <axboe@kernel.dk>,
        Christoph Hellwig <hch@infradead.org>,
        linux-block@vger.kernel.org,
        linux-m68k <linux-m68k@lists.linux-m68k.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
From:   Michael Schmitz <schmitzmic@gmail.com>
Message-ID: <ee78b20c-36f0-408d-87d0-b8b75a66110d@gmail.com>
Date:   Tue, 16 Nov 2021 08:23:27 +1300
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On 12/11/21 20:51, Geert Uytterhoeven wrote:
[...]
>>>>>> BTW, today I just found that hang in blk_mq_freeze_queue_wait() is
>>>>>> caused by commit 900e080752025f00, and the following patch can fix it:
>>>>>>
>>>>>> - blk-mq: don't grab ->q_usage_counter in blk_mq_sched_bio_merge
>>>>>>
>>>>>> https://lore.kernel.org/linux-block/20211111085650.GA476@lst.de/T/#m759b88fda094a65ebf29bc81b780967cdaf9cf28
>>>>>>
>>>>>> Maybe you can try the above patch.
>>>>>
>>>>> Thanks! I have applied both patches, but it doesn't make a difference.
>>>>
>>>> Thanks for your test!
>>>>
>>>> Can you try the following patch?
>
> [...]
>
>>> That's definitely a real fix, akin to the other pre-enter variants, this
>>> one just post checks. Geert, can you give this a whirl?
>
> With both of
>
>     blk-mq: don't grab ->q_usage_counter in blk_mq_sched_bio_merge
>     blk-mq: rename blk_attempt_bio_merge
>
> applied, and the version above, I no longer saw the error, but the
> boot sometimes hangs after:
>
>     ext3 filesystem being remounted at / supports timestamps until
> 2038 (0x7fffffff)
>
> I don't know how easy that is to trigger: it hung on my first try, but
> the second and third tries it booted fully into old Debian userspace.
>
>>> Ming, would you mind sending this as a real patch?
>>
>> The above patch may not be enough, since submit_bio_checks() is done in
>> case of using cached request, so how about the following patch(un-tested)?
>
> Worked fine in five subsequent boots. Thanks!
> Tested-by: Geert Uytterhoeven <geert@linux-m68k.org>

For good measure: block-5.16-2021-11-13 tested fine running IO stress 
tests on a mix of IDE and SCSI disks, only one of those supporting DPO/FUA.

Using

WARN_ON(rq->cmd_flags & REQ_FUA && !sdkp->DPOFUA);

in sd.c:sd_setup_read_write_cmnd(), nothing seen in the logs.

Cheers,

	Michael


>
> Gr{oetje,eeting}s,
>
>                         Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds
>