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From:   Eric Dumazet <edumazet@google.com>
Date:   Tue, 21 Dec 2021 08:03:56 -0800
Message-ID: <CANn89iJfEgkJCBqO9d7t9BHHMEh-6DQ1BJkqkiOQ59dxSHB2EQ@mail.gmail.com>
Subject: Re: [syzbot] general protection fault in set_task_ioprio
To:     Jens Axboe <axboe@kernel.dk>
Cc:     syzbot <syzbot+8836466a79f4175961b0@syzkaller.appspotmail.com>,
        Christoph Hellwig <hch@lst.de>, 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 7:25 AM Jens Axboe <axboe@kernel.dk> wrote:
>
> On 12/21/21 3:44 AM, Eric Dumazet wrote:
> > 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>
>
> 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
>