linux-kernel - Re: md_raid: mdX_raid6 looping after sync

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Message-ID: <CAH6h+hcWfXNpC1Mro3zfzQc8tK142vuaOMELLJL7mg_G+o0fXw@mail.gmail.com>
Date:   Thu, 16 Mar 2023 11:25:41 -0400
From:   Marc Smith <msmith626@...il.com>
To:     Guoqing Jiang <guoqing.jiang@...ux.dev>
Cc:     Donald Buczek <buczek@...gen.mpg.de>, Song Liu <song@...nel.org>,
        linux-raid@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        it+raid@...gen.mpg.de
Subject: Re: md_raid: mdX_raid6 looping after sync_action "check" to "idle" transition

On Tue, Mar 14, 2023 at 10:45 AM Marc Smith <msmith626@...il.com> wrote:
>
> On Tue, Mar 14, 2023 at 9:55 AM Guoqing Jiang <guoqing.jiang@...ux.dev> wrote:
> >
> >
> >
> > On 3/14/23 21:25, Marc Smith wrote:
> > > On Mon, Feb 8, 2021 at 7:49 PM Guoqing Jiang
> > > <guoqing.jiang@...ud.ionos.com> wrote:
> > >> Hi Donald,
> > >>
> > >> On 2/8/21 19:41, Donald Buczek wrote:
> > >>> Dear Guoqing,
> > >>>
> > >>> On 08.02.21 15:53, Guoqing Jiang wrote:
> > >>>>
> > >>>> On 2/8/21 12:38, Donald Buczek wrote:
> > >>>>>> 5. maybe don't hold reconfig_mutex when try to unregister
> > >>>>>> sync_thread, like this.
> > >>>>>>
> > >>>>>>           /* resync has finished, collect result */
> > >>>>>>           mddev_unlock(mddev);
> > >>>>>>           md_unregister_thread(&mddev->sync_thread);
> > >>>>>>           mddev_lock(mddev);
> > >>>>> As above: While we wait for the sync thread to terminate, wouldn't it
> > >>>>> be a problem, if another user space operation takes the mutex?
> > >>>> I don't think other places can be blocked while hold mutex, otherwise
> > >>>> these places can cause potential deadlock. Please try above two lines
> > >>>> change. And perhaps others have better idea.
> > >>> Yes, this works. No deadlock after >11000 seconds,
> > >>>
> > >>> (Time till deadlock from previous runs/seconds: 1723, 37, 434, 1265,
> > >>> 3500, 1136, 109, 1892, 1060, 664, 84, 315, 12, 820 )
> > >> Great. I will send a formal patch with your reported-by and tested-by.
> > >>
> > >> Thanks,
> > >> Guoqing
> > > I'm still hitting this issue with Linux 5.4.229 -- it looks like 1/2
> > > of the patches that supposedly resolve this were applied to the stable
> > > kernels, however, one was omitted due to a regression:
> > > md: don't unregister sync_thread with reconfig_mutex held (upstream
> > > commit 8b48ec23cc51a4e7c8dbaef5f34ebe67e1a80934)
> > >
> > > I don't see any follow-up on the thread from June 8th 2022 asking for
> > > this patch to be dropped from all stable kernels since it caused a
> > > regression.
> > >
> > > The patch doesn't appear to be present in the current mainline kernel
> > > (6.3-rc2) either. So I assume this issue is still present there, or it
> > > was resolved differently and I just can't find the commit/patch.
> >
> > It should be fixed by commit 9dfbdafda3b3"md: unlock mddev before reap
> > sync_thread in action_store".
>
> Okay, let me try applying that patch... it does not appear to be
> present in my 5.4.229 kernel source. Thanks.

Yes, applying this '9dfbdafda3b3 "md: unlock mddev before reap
sync_thread in action_store"' patch on top of vanilla 5.4.229 source
appears to fix the problem for me -- I can't reproduce the issue with
the script, and it's been running for >24 hours now. (Previously I was
able to induce the issue within a matter of minutes.)


>
> --Marc
>
>
> >
> > Thanks,
> > Guoqing