linux-kernel - Re: INFO: task hung in generic_file_write

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Date:   Tue, 31 Jul 2018 00:07:22 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        syzbot <syzbot+9933e4476f365f5d5a1b@...kaller.appspotmail.com>,
        linux-mm@...ck.org, mgorman@...hsingularity.net,
        Michal Hocko <mhocko@...nel.org>, ak@...ux.intel.com,
        jack@...e.cz, jlayton@...hat.com, linux-kernel@...r.kernel.org,
        mawilcox@...rosoft.com, syzkaller-bugs@...glegroups.com,
        tim.c.chen@...ux.intel.com,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: INFO: task hung in generic_file_write_iter

On 2018/07/21 5:06, Andrew Morton wrote:
> On Fri, 20 Jul 2018 19:36:23 +0900 Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp> wrote:
> 
>>>
>>> This report is stalling after mount() completed and process used remap_file_pages().
>>> I think that we might need to use debug printk(). But I don't know what to examine.
>>>
>>
>> Andrew, can you pick up this debug printk() patch?
>> I guess we can get the result within one week.
> 
> Sure, let's toss it in -next for a while.
> 
>> >From 8f55e00b21fefffbc6abd9085ac503c52a302464 Mon Sep 17 00:00:00 2001
>> From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
>> Date: Fri, 20 Jul 2018 19:29:06 +0900
>> Subject: [PATCH] fs/buffer.c: add debug print for __getblk_gfp() stall problem
>>
>> Among syzbot's unresolved hung task reports, 18 out of 65 reports contain
>> __getblk_gfp() line in the backtrace. Since there is a comment block that
>> says that __getblk_gfp() will lock up the machine if try_to_free_buffers()
>> attempt from grow_dev_page() is failing, let's start from checking whether
>> syzbot is hitting that case. This change will be removed after the bug is
>> fixed.
> 
> I'm not sure that grow_dev_page() is hanging.  It has often been
> suspected, but always is proven innocent.  Lets see.

syzbot reproduced this problem ( https://syzkaller.appspot.com/text?tag=CrashLog&x=11f2fc44400000 ) .
It says that grow_dev_page() is returning 1 but __find_get_block() is failing forever. Any idea?