linux-kernel - Re: Infiniate systemd loop when power off the machine with multiple MD RAIDs

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Message-ID: <CAMz9Wg-dcBFnw-3SfsD6Lrhp4o7cVf_w7y2X7yQ_hWCg+CiRXQ@mail.gmail.com>
Date:   Mon, 28 Aug 2023 18:48:58 +0800
From:   AceLan Kao <acelan@...il.com>
To:     Song Liu <song@...nel.org>
Cc:     Guoqing Jiang <guoqing.jiang@...ux.dev>,
        Mariusz Tkaczyk <mariusz.tkaczyk@...ux.intel.com>,
        Bagas Sanjaya <bagasdotme@...il.com>,
        Christoph Hellwig <hch@....de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Regressions <regressions@...ts.linux.dev>,
        Linux RAID <linux-raid@...r.kernel.org>
Subject: Re: Infiniate systemd loop when power off the machine with multiple
 MD RAIDs

Hi Song,

Song Liu <song@...nel.org> 於 2023年8月28日 週一 下午1:21寫道：
>
> Hi AceLan,
>
> Thanks for running the experiments.
>
> On Fri, Aug 25, 2023 at 9:32 PM AceLan Kao <acelan@...il.com> wrote:
> [...]
> > >
> > > Could you please run the follow two experiments?
> > >
> > > 1. Confirm 12a6caf273240a triggers this. Specifically:
> > >    git checkout 12a6caf273240a => repros
> > >    git checkout 12a6caf273240a~1 => cannot repro
> > Yes, I'm pretty sure about this, that's my bisect result and I just
> > confirmed it again.
> > I also tried reverting 12a6caf273240a and the issue is gone.
>
> The log doesn't match my guess. Specifically:
>
> [  420.068142] systemd-shutdown[1]: Stopping MD /dev/md123 (9:123).
> [  420.074718] md_open:md123 openers++ = 1 by systemd-shutdow
> [  420.080787] systemd-shutdown[1]: Failed to sync MD block device
> /dev/md123, ignoring: Input/output error
> [  420.090831] md: md123 stopped.
> [  420.094465] systemd-shutdown[1]: Stopping MD /dev/md122 (9:122).
> [  420.101045] systemd-shutdown[1]: Could not stop MD /dev/md122:
> Device or resource busy
>
> For a successful stop on md123, we reach the pr_info() in md_open().
> For a failed stop on md122, the kernel returns -EBUSY before that
> pr_info() in md_open(). There are some changes in md_open() in
> the past few release, so I am not quite sure we are looking at the
> same code.
>
> Therefore, could you please help clarify:
>
> 1. Which base kernel are you using?
>
> From the log, you are using 6.5-rc7-706a74159504. However,
> I think we cannot cleanly revert 12a6caf273240a on top of
> 6.5-rc7-706a74159504. Did you manually fix some issue in the
> revert? If so, could you please share the revert commit?
Yes, I'm basing 6.5.0-rc7 706a74159504 to apply your patch
706a74159504 Linux 6.5-rc7

Attached how I revert the commit.

>
> 2. If you are not using 6.5-rc7-706a74159504 as base kernel, which
> one are you using?
>
> Thanks,
> Song
>
> >
> > >
> > > 2. Try with the following change (add debug messages), which hopefully
> > >    shows which command is holding a reference on mddev->openers.
> > >
> > > Thanks,
> > > Song
> > >
> > > diff --git i/drivers/md/md.c w/drivers/md/md.c
> > > index 78be7811a89f..3e9b718b32c1 100644
> > > --- i/drivers/md/md.c
> > > +++ w/drivers/md/md.c
> > > @@ -7574,11 +7574,15 @@ static int md_ioctl(struct block_device *bdev,
> > > blk_mode_t mode,
> > >                 if (mddev->pers && atomic_read(&mddev->openers) > 1) {
> > >                         mutex_unlock(&mddev->open_mutex);
> > >                         err = -EBUSY;
> > > +                       pr_warn("%s return -EBUSY for %s with
> > > mddev->openers = %d\n",
> > > +                               __func__, mdname(mddev),
> > > atomic_read(&mddev->openers));
> > >                         goto out;
> > >                 }
> > >                 if (test_and_set_bit(MD_CLOSING, &mddev->flags)) {
> > >                         mutex_unlock(&mddev->open_mutex);
> > >                         err = -EBUSY;
> > > +                       pr_warn("%s return -EBUSY for %s with
> > > MD_CLOSING bit set\n",
> > > +                               __func__, mdname(mddev));
> > >                         goto out;
> > >                 }
> > >                 did_set_md_closing = true;
> > > @@ -7789,6 +7793,8 @@ static int md_open(struct gendisk *disk, blk_mode_t mode)
> > >                 goto out_unlock;
> > >
> > >         atomic_inc(&mddev->openers);
> > > +       pr_info("%s:%s openers++ = %d by %s\n", __func__, mdname(mddev),
> > > +               atomic_read(&mddev->openers), current->comm);
> > >         mutex_unlock(&mddev->open_mutex);
> > >
> > >         disk_check_media_change(disk);
> > > @@ -7807,6 +7813,8 @@ static void md_release(struct gendisk *disk)
> > >
> > >         BUG_ON(!mddev);
> > >         atomic_dec(&mddev->openers);
> > > +       pr_info("%s:%s openers-- = %d by %s\n", __func__, mdname(mddev),
> > > +               atomic_read(&mddev->openers), current->comm);
> > >         mddev_put(mddev);
> > >  }
> > It's pretty strange that I can't reproduce the issue after applied the patch.
> >
> > I tried to figure out which part affect the issue and found when I
> > comment out the pr_info() In md_release(), the issue could be
> > reproduced.
> >
> > --
> > Chia-Lin Kao(AceLan)
> > http://blog.acelan.idv.tw/
> > E-Mail: acelan.kaoATcanonical.com (s/AT/@/)



-- 
Chia-Lin Kao(AceLan)
http://blog.acelan.idv.tw/
E-Mail: acelan.kaoATcanonical.com (s/AT/@/)

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