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Subject: Re: INFO: task hung in generic_file_write_iter
From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
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Date: Mon, 20 Aug 2018 23:12:10 +0900
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Sender: owner-linux-mm@kvack.org
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To: Jan Kara <jack@suse.cz>, Andrew Morton <akpm@linux-foundation.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>, syzbot <syzbot+9933e4476f365f5d5a1b@syzkaller.appspotmail.com>, linux-mm@kvack.org, mgorman@techsingularity.net, Michal Hocko <mhocko@kernel.org>, ak@linux.intel.com, jlayton@redhat.com, linux-kernel@vger.kernel.org, mawilcox@microsoft.com, syzkaller-bugs@googlegroups.com, tim.c.chen@linux.intel.com, linux-fsdevel <linux-fsdevel@vger.kernel.org>

On 2018/08/06 20:56, Tetsuo Handa wrote:
> On 2018/08/06 19:09, Jan Kara wrote:
>> Looks like some kind of a race where device block size gets changed while
>> getblk() runs (and creates buffers for underlying page). I don't have time
>> to nail it down at this moment can have a look into it later unless someone
>> beats me to it.
>>
> 
> It seems that loop device is relevant to this problem.

Speak of loop device, I'm waiting for Jens for three months
http://lkml.kernel.org/r/1527297408-4428-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp
but Jens is too busy to come up with an alternative. Since that is a big patch, I wish we can
start testing that patch before Jan starts writing a patch for fixing getblk() race problem.