Re: md_raid: mdX_raid6 looping after sync_action "check" to "idle" transition

From: Guoqing Jiang <guoqing.jiang@linux.dev>
To: Marc Smith <msmith626@gmail.com>
Cc: Donald Buczek <buczek@molgen.mpg.de>, Song Liu <song@kernel.org>,
	linux-raid@vger.kernel.org,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	it+raid@molgen.mpg.de
Subject: Re: md_raid: mdX_raid6 looping after sync_action "check" to "idle" transition
Date: Tue, 14 Mar 2023 21:55:08 +0800	[thread overview]
Message-ID: <2af18cf7-05eb-f1d1-616a-2c5894d1ac43@linux.dev> (raw)
In-Reply-To: <CAH6h+hf7Y-kurBJG+pnH6WCQiaEK+Jq3KG5JOGnHJ4Uw6AbUjg@mail.gmail.com>

On 3/14/23 21:25, Marc Smith wrote:
> On Mon, Feb 8, 2021 at 7:49 PM Guoqing Jiang
> <guoqing.jiang@cloud.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".

Thanks,
Guoqing