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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Fri, 12 Nov 2021 08:51:12 +0100
Message-ID: <CAMuHMdV30yvjam8i0Z4Nsu=e1YhPaRb4E1bAtw7=268v6TnrJg@mail.gmail.com>
Subject: Re: [PATCH 4/5] block: move queue enter logic into blk_mq_submit_bio()
To:     Ming Lei <ming.lei@redhat.com>
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>
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Hi Ming,

On Fri, Nov 12, 2021 at 1:44 AM Ming Lei <ming.lei@redhat.com> wrote:
> On Thu, Nov 11, 2021 at 03:17:27PM -0700, Jens Axboe wrote:
> > On 11/11/21 8:23 AM, Ming Lei wrote:
> > > On Thu, Nov 11, 2021 at 03:51:28PM +0100, Geert Uytterhoeven wrote:
> > >> On Thu, Nov 11, 2021 at 2:45 PM Ming Lei <ming.lei@redhat.com> wrote:
> > >>> On Thu, Nov 11, 2021 at 01:58:38PM +0100, Geert Uytterhoeven wrote:
> > >>>> On Thu, 4 Nov 2021, Jens Axboe wrote:
> > >>>>> On 11/4/21 1:04 PM, Christoph Hellwig wrote:
> > >>>>>> On Thu, Nov 04, 2021 at 01:02:54PM -0600, Jens Axboe wrote:
> > >>>>>>> On 11/4/21 12:52 PM, Christoph Hellwig wrote:
> > >>>>>>>> Looks good:
> > >>>>>>>>
> > >>>>>>>> Reviewed-by: Christoph Hellwig <hch@lst.de>
> > >>>>>>>
> > >>>>>>> So these two are now:
> > >>>>>>>
> > >>>>>>> https://git.kernel.dk/cgit/linux-block/commit/?h=for-5.16/block&id=c98cb5bbdab10d187aff9b4e386210eb2332af96
> > >>>>>>>
> > >>>>>>> which is the one I sent here, and then the next one gets cleaned up to
> > >>>>>>> remove that queue enter helper:
> > >>>>>>>
> > >>>>>>> https://git.kernel.dk/cgit/linux-block/commit/?h=for-5.16/block&id=7f930eb31eeb07f1b606b3316d8ad3ab6a92905b
> > >>>>>>>
> > >>>>>>> Can I add your reviewed-by to this last one as well? Only change is the
> > >>>>>>> removal of blk_mq_enter_queue() and the weird construct there, it's just
> > >>>>>>> bio_queue_enter() now.
> > >>>>>>
> > >>>>>> Sure.
> > >>>>>
> > >>>>> Thanks, prematurely already done, as you could tell :-)
> > >>>>
> > >>>> The updated version is now commit 900e080752025f00 ("block: move queue
> > >>>> enter logic into blk_mq_submit_bio()") in Linus' tree.
> > >>>>
> > >>>> I have bisected failures on m68k/atari (on ARAnyM, using nfhd as the
> > >>>> root device) to this commit, e.g.:
> > >>>>
> > >>>>     sd 0:0:0:0: [sda] tag#0 FAILED Result: hostbyte=DID_OK driverbyte=DRIVER_OK cmd_age=0s
> > >>>>     sd 0:0:0:0: [sda] tag#0 Sense Key : Illegal Request [current]
> > >>>>     sd 0:0:0:0: [sda] tag#0 Add. Sense: Invalid field in cdb
> > >>>>     sd 0:0:0:0: [sda] tag#0 CDB: Write(10) 2a 08 00 00 00 01 00 00 08 00
> > >>>>     critical target error, dev sda, sector 1 op 0x1:(WRITE) flags 0x20800 phys_seg 1 prio class 0
> > >>>>     Buffer I/O error on dev sda1, logical block 0, lost sync page write
> > >>>>
> > >>>>     EXT4-fs (sda1): I/O error while writing superblock
> > >>>>     sd 0:0:0:0: [sda] tag#0 FAILED Result: hostbyte=DID_OK driverbyte=DRIVER_OK cmd_age=0s
> > >>>>     sd 0:0:0:0: [sda] tag#0 Sense Key : Illegal Request [current]
> > >>>>     sd 0:0:0:0: [sda] tag#0 Add. Sense: Invalid field in cdb
> > >>>>     sd 0:0:0:0: [sda] tag#0 CDB: Write(10) 2a 08 00 00 00 01 00 00 08 00
> > >>>>     critical target error, dev sda, sector 1 op 0x1:(WRITE) flags 0x20800 phys_seg 1 prio class 0
> > >>>>     Buffer I/O error on dev sda1, logical block 0, lost sync page write
> > >>>>     EXT4-fs (sda1): I/O error while writing superblock
> > >>>>
> > >>>> This may happen either when mounting the root file system (leading to an
> > >>>> unable to mount root fs panic), or later (leading to a read-only
> > >>>> rootfs).
> > >>>
> > >>> 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>

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