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Subject: Re: md_raid: mdX_raid6 looping after sync_action "check" to "idle"
 transition
To:     Guoqing Jiang <guoqing.jiang@cloud.ionos.com>,
        Song Liu <song@kernel.org>, linux-raid@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        it+raid@molgen.mpg.de
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From:   Donald Buczek <buczek@molgen.mpg.de>
Message-ID: <7733de01-d1b0-e56f-db6a-137a752f7236@molgen.mpg.de>
Date:   Mon, 8 Feb 2021 19:41:14 +0100
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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 )

Best
   Donald
> 
> Thanks,
> Guoqing