Re: [syzbot] general protection fault in set_task_ioprio

Re: [syzbot] general protection fault in set_task_ioprio

[syzbot]

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

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

Re: [syzbot] general protection fault in set_task_ioprio

[Eric Dumazet]

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

Re: [syzbot] general protection fault in set_task_ioprio

[Jens Axboe]

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.

-- 
Jens Axboe

Re: [syzbot] general protection fault in set_task_ioprio

[Eric Dumazet]

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
>

Re: [syzbot] general protection fault in set_task_ioprio

[Jens Axboe]

On 12/21/21 9:03 AM, Eric Dumazet wrote:
> 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)

Ah got it, yes makes sense.

> linux-next has still this bug in set_task_ioprio()

linux-next often trails by a few days, once it catches up hopefully
this will be behind us.

-- 
Jens Axboe