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From: Vegard Nossum <vegard.nossum@gmail.com>
Date: Mon, 5 Dec 2016 21:10:57 +0100
Message-ID: <CAOMGZ=G_wM13ikKt7cTUt1gppsf4TAzFwg2kybUYMvEuzJyj2w@mail.gmail.com>
Subject: Re: bio linked list corruption.
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Dave Jones <davej@codemonkey.org.uk>, Chris Mason <clm@fb.com>,
        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>
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Sender: linux-kernel-owner@vger.kernel.org
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On 5 December 2016 at 20:11, Vegard Nossum <vegard.nossum@gmail.com> wrote:
> On 5 December 2016 at 18:55, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
>> On Mon, Dec 5, 2016 at 9:09 AM, Vegard Nossum <vegard.nossum@gmail.com> wrote:
>> Since you apparently can recreate this fairly easily, how about trying
>> this stupid patch?
>>
>> NOTE! This is entirely untested. I may have screwed this up entirely.
>> You get the idea, though - just remove the wait queue head from the
>> list - the list entries stay around, but nothing points to the stack
>> entry (that we're going to free) any more.
>>
>> And add the warning to see if this actually ever triggers (and because
>> I'd like to see the callchain when it does, to see if it's another
>> waitqueue somewhere or what..)
>
> ------------[ cut here ]------------
> WARNING: CPU: 22 PID: 14012 at mm/shmem.c:2668 shmem_fallocate+0x9a7/0xac0
> Kernel panic - not syncing: panic_on_warn set ...

So I noticed that panic_on_warn just after sending the email and I've
been waiting for it it to trigger again.

The warning has triggered twice more without panic_on_warn set and I
haven't seen any crash yet.


Vegard