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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Mon, 31 Oct 2016 12:35:16 -0700
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Subject: Re: bio linked list corruption.
To: Dave Jones <davej@codemonkey.org.uk>, Chris Mason <clm@fb.com>,
        Jens Axboe <axboe@fb.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andy Lutomirski <luto@amacapital.net>,
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        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 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.

 Linus