linux-kernel - Re: bio linked list corruption.

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Message-ID: <CA+55aFzEG-6pkJXy4itiXsHPu_VV5q2vd6zJLq6vmi=AzdnaUw@mail.gmail.com>
Date:   Mon, 5 Dec 2016 12:10:29 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Vegard Nossum <vegard.nossum@...il.com>
Cc:     Dave Jones <davej@...emonkey.org.uk>, Chris Mason <clm@...com>,
        Jens Axboe <axboe@...com>,
        Andy Lutomirski <luto@...capital.net>,
        Andy Lutomirski <luto@...nel.org>,
        Al Viro <viro@...iv.linux.org.uk>, Josef Bacik <jbacik@...com>,
        David Sterba <dsterba@...e.com>,
        linux-btrfs <linux-btrfs@...r.kernel.org>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        Dave Chinner <david@...morbit.com>
Subject: Re: bio linked list corruption.

On Mon, Dec 5, 2016 at 11:11 AM, Vegard Nossum <vegard.nossum@...il.com> wrote:
>
> ------------[ cut here ]------------
> WARNING: CPU: 22 PID: 14012 at mm/shmem.c:2668 shmem_fallocate+0x9a7/0xac0

Ok, good. So that's confirmed as the cause of this problem.

And the call chain that I wanted is obviously completely
uninteresting, because it's call cghain on the other side (the page
fault side) that would show the nested wake queue behavior. I was just
being stupid about it.

I wonder if we have any other places where we just blithely assume
that "wake_up_all()" will actually empty the whole wait queue. It's
_usually_ true, but as noted, nested waiting does happen.

Anyway, can you try this patch instead? It should actually cause the
wake_up_all() to always remove all entries, and thus the WARN_ON()
should no longer happen (and I removed the "list_del()" hackery).

                       Linus

View attachment "patch.diff" of type "text/plain" (1440 bytes)