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From:   Eric Dumazet <edumazet@google.com>
Date:   Tue, 21 Dec 2021 02:44:36 -0800
Message-ID: <CANn89i++5O_4_j3KO0wAiJHkEj=1zAeAHv=s9Lub_B6=cguwXQ@mail.gmail.com>
Subject: Re: [syzbot] general protection fault in set_task_ioprio
To:     syzbot <syzbot+8836466a79f4175961b0@syzkaller.appspotmail.com>,
        Christoph Hellwig <hch@lst.de>
Cc:     Jens Axboe <axboe@kernel.dk>, changbin.du@intel.com,
        Christian Brauner <christian.brauner@ubuntu.com>,
        Daniel Borkmann <daniel@iogearbox.net>,
        David Miller <davem@davemloft.net>,
        Heiner Kallweit <hkallweit1@gmail.com>,
        Jakub Kicinski <kuba@kernel.org>, linux-block@vger.kernel.org,
        LKML <linux-kernel@vger.kernel.org>,
        netdev <netdev@vger.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        Yajun Deng <yajun.deng@linux.dev>
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On Tue, Dec 21, 2021 at 1:52 AM syzbot
<syzbot+8836466a79f4175961b0@syzkaller.appspotmail.com> wrote:
>
> syzbot has bisected this issue to:
>
> commit e4b8954074f6d0db01c8c97d338a67f9389c042f
> Author: Eric Dumazet <edumazet@google.com>
> Date:   Tue Dec 7 01:30:37 2021 +0000
>
>     netlink: add net device refcount tracker to struct ethnl_req_info
>

Unfortunately this commit will be in the way of many bisections.

Real bug was added in

commit 5fc11eebb4a98df5324a4de369bb5ab7f0007ff7
Author: Christoph Hellwig <hch@lst.de>
Date:   Thu Dec 9 07:31:29 2021 +0100

    block: open code create_task_io_context in set_task_ioprio

    The flow in set_task_ioprio can be simplified by simply open coding
    create_task_io_context, which removes a refcount roundtrip on the I/O
    context.

    Signed-off-by: Christoph Hellwig <hch@lst.de>
    Reviewed-by: Jan Kara <jack@suse.cz>
    Link: https://lore.kernel.org/r/20211209063131.18537-10-hch@lst.de
    Signed-off-by: Jens Axboe <axboe@kernel.dk>


> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=10620fcdb00000
> start commit:   07f8c60fe60f Add linux-next specific files for 20211220
> git tree:       linux-next
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=12620fcdb00000
> console output: https://syzkaller.appspot.com/x/log.txt?x=14620fcdb00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=2060504830b9124a
> dashboard link: https://syzkaller.appspot.com/bug?extid=8836466a79f4175961b0
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12058fcbb00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17141adbb00000
>
> Reported-by: syzbot+8836466a79f4175961b0@syzkaller.appspotmail.com
> Fixes: e4b8954074f6 ("netlink: add net device refcount tracker to struct ethnl_req_info")
>
> For information about bisection process see: https://goo.gl/tpsmEJ#bisection