Date: Mon, 31 Oct 2016 13:44:55 -0600
From: Chris Mason <clm@fb.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
CC: Dave Jones <davej@codemonkey.org.uk>, Jens Axboe <axboe@fb.com>,
        "Andy Lutomirski" <luto@amacapital.net>,
        Andy Lutomirski <luto@kernel.org>, Al Viro <viro@zeniv.linux.org.uk>,
        Josef Bacik <jbacik@fb.com>, David Sterba <dsterba@suse.com>,
        linux-btrfs <linux-btrfs@vger.kernel.org>,
        Linux Kernel <linux-kernel@vger.kernel.org>,
        Dave Chinner <david@fromorbit.com>
Subject: Re: bio linked list corruption.
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        Andy Lutomirski <luto@kernel.org>,
        Al Viro <viro@zeniv.linux.org.uk>, Josef Bacik <jbacik@fb.com>,
        David Sterba <dsterba@suse.com>,
        linux-btrfs <linux-btrfs@vger.kernel.org>,
        Linux Kernel <linux-kernel@vger.kernel.org>,
        Dave Chinner <david@fromorbit.com>
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On Mon, Oct 31, 2016 at 12:35:16PM -0700, Linus Torvalds wrote:
>On Mon, Oct 31, 2016 at 11:55 AM, Dave Jones <davej@codemonkey.org.uk> wrote:
>>
>> BUG: Bad page state in process kworker/u8:12  pfn:4e0e39
>> page:ffffea0013838e40 count:0 mapcount:0 mapping:ffff8804a20310e0 index:0x100c
>> flags: 0x400000000000000c(referenced|uptodate)
>> page dumped because: non-NULL mapping
>
>Hmm. So this seems to be btrfs-specific, right?
>
>I searched for all your "non-NULL mapping" cases, and they all seem to
>have basically the same call trace, with some work thread doing
>writeback and going through btrfs_writepages().
>
>Sounds like it's a race with either fallocate hole-punching or
>truncate. I'm not seeing it, but I suspect it's btrfs, since DaveJ
>clearly ran other filesystems too but I am not seeing this backtrace
>for anything else.

Agreed, I think this is a separate bug, almost certainly btrfs specific.  
I'll work with Dave on a better reproducer.

-chris