Re: [syzbot] general protection fault in set_task_ioprio

[Eric Dumazet]

On Tue, Dec 21, 2021 at 7:25 AM Jens Axboe <axboe@xxxxxxxxx> wrote:
>
> On 12/21/21 3:44 AM, Eric Dumazet wrote:
> > 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>
>
> There are only really 5 patches in between the broken commit and the one
> that fixes it, and it only affects things trying to set the ioprio with
> a dead task. Is this a huge issue? I don't see why this would cause a
> lot of bisection headaches.
>

I was saying that my commit was polluting syzbot bisection, this is a
distraction in this report.
(Or if you prefer, please ignore syzbot bisection)

linux-next has still this bug in set_task_ioprio()


> --
> Jens Axboe
>