linux-ext4 - Re: WARNING in ext4_set_page

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Date:   Wed, 13 Jun 2018 17:55:42 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Jan Kara <jack@...e.cz>
Cc:     syzbot <syzbot+9a44753ac327c557796a@...kaller.appspotmail.com>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        linux-ext4@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        "Theodore Ts'o" <tytso@....edu>
Subject: Re: WARNING in ext4_set_page_dirty

On Mon, May 21, 2018 at 2:50 PM, Jan Kara <jack@...e.cz> wrote:
> On Sun 20-05-18 23:07:02, syzbot wrote:
>> syzbot has found a reproducer for the following crash on:
>>
>> HEAD commit:    771c577c23ba Linux 4.17-rc6
>> git tree:       upstream
>> console output: https://syzkaller.appspot.com/x/log.txt?x=108c9f37800000
>> kernel config:  https://syzkaller.appspot.com/x/.config?x=982e2df1b9e60b02
>> dashboard link: https://syzkaller.appspot.com/bug?extid=9a44753ac327c557796a
>> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
>> syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=1655584f800000
>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15134357800000
>>
>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>> Reported-by: syzbot+9a44753ac327c557796a@...kaller.appspotmail.com
>>
>> WARNING: CPU: 0 PID: 4577 at fs/ext4/inode.c:3894
>> ext4_set_page_dirty+0x28d/0x330 fs/ext4/inode.c:3894
>> Kernel panic - not syncing: panic_on_warn set ...
>
> Looking at the reproducer, this is the issue we have been speaking about at
> LSF/MM - direct IO read dirties pages after writeback has written them out
> and so we don't expect them to be dirtied. If someone told me I would not
> believe this is possible to hit by fuzzing ;) Good job from the syzkaller
> guys!

Thanks, Jan! Very nice to hear.
I believe we are not yet at the limit of what's possible :)