Re: [syzbot] general protection fault in set_task_ioprio

[Eric Dumazet]

On Tue, Dec 21, 2021 at 1:52 AM syzbot
<syzbot+8836466a79f4175961b0@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> syzbot has bisected this issue to:
>
> commit e4b8954074f6d0db01c8c97d338a67f9389c042f
> Author: Eric Dumazet <edumazet@xxxxxxxxxx>
> 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@xxxxxx>
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@xxxxxx>
    Reviewed-by: Jan Kara <jack@xxxxxxx>
    Link: https://lore.kernel.org/r/20211209063131.18537-10-hch@xxxxxx
    Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>


> 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@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: e4b8954074f6 ("netlink: add net device refcount tracker to struct ethnl_req_info")
>
> For information about bisection process see: https://goo.gl/tpsmEJ#bisection