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Subject: Re: md_raid: mdX_raid6 looping after sync_action "check" to "idle"
 transition
To:     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
References: <aa9567fd-38e1-7b9c-b3e1-dc2fdc055da5@molgen.mpg.de>
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From:   Guoqing Jiang <guoqing.jiang@cloud.ionos.com>
Message-ID: <d92922af-f411-fc53-219f-154de855cd13@cloud.ionos.com>
Date:   Tue, 9 Feb 2021 01:46:26 +0100
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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