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Date:   Fri, 25 Jan 2019 09:04:46 +0100
From:   "Stephen R. van den Berg" <srb@cuci.nl>
To:     Qu Wenruo <quwenruo.btrfs@gmx.com>
Cc:     Btrfs BTRFS <linux-btrfs@vger.kernel.org>
Subject: Re: New hang (Re: Kernel traces), sysreq+w output
Message-ID: <20190125080446.GB27316@cuci.nl>
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Stephen R. van den Berg wrote:
>Stephen R. van den Berg wrote:
>>Stephen R. van den Berg wrote:
>>>Qu Wenruo wrote:
>>>>>> It's caused by qgroup, and a dead lock on btrfs_drop_snapshot().

>>>>>> Please either disable qgroup or apply this patch to solve it:
>>>>>> https://patchwork.kernel.org/patch/10725371/

>>>Ok, booting the system in v4.20 with this patch.  I'll report back if
>>>it does not resolve the problem.

I'm running v4.20.0 with this patch on this system, BTW.
-- 
Stephen.