linux-kernel - Re: WARNING in ext4_set_page

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Message-ID: <20180521125000.hlgdsvlzlr7xw3bx@quack2.suse.cz>
Date:   Mon, 21 May 2018 14:50:00 +0200
From:   Jan Kara <jack@...e.cz>
To:     syzbot <syzbot+9a44753ac327c557796a@...kaller.appspotmail.com>
Cc:     adilger.kernel@...ger.ca, jack@...e.cz, linux-ext4@...r.kernel.org,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        tytso@....edu
Subject: Re: WARNING in ext4_set_page_dirty

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!

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR