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Date:   Mon, 15 Apr 2019 21:35:08 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Alan Stern <stern@...land.harvard.edu>,
        Kernel development list <linux-kernel@...r.kernel.org>,
        USB list <linux-usb@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: INFO: task hung in usb_kill_urb

On Mon, Apr 15, 2019 at 9:09 PM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> On Mon, Apr 15, 2019 at 01:39:57PM -0500, Gustavo A. R. Silva wrote:
> >
> >
> > On 4/15/19 12:48 PM, Andrey Konovalov wrote:
> > > On Fri, Apr 12, 2019 at 9:46 PM Alan Stern <stern@...land.harvard.edu> wrote:
> > >>
> > >> Andrey:
> > >>
> > >> It's really hard to tell just what's going on here.
> > >>
> > >> On Fri, 12 Apr 2019, syzbot wrote:
> > >>
> > >>> Hello,
> > >>>
> > >>> syzbot found the following crash on:
> > >>>
> > >>> HEAD commit:    9a33b369 usb-fuzzer: main usb gadget fuzzer driver
> > >>> git tree:       https://github.com/google/kasan/tree/usb-fuzzer
> > >>> console output: https://syzkaller.appspot.com/x/log.txt?x=14c4c1af200000
> > >>> kernel config:  https://syzkaller.appspot.com/x/.config?x=23e37f59d94ddd15
> > >>> dashboard link: https://syzkaller.appspot.com/bug?extid=d919b0f29d7b5a4994b9
> > >>> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> > >>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14410dbb200000
> > >>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12f0acd3200000
> > >>>
> > >>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > >>> Reported-by: syzbot+d919b0f29d7b5a4994b9@...kaller.appspotmail.com
> > >>>
> > >>> usb-fuzzer-gadget dummy_udc.0: failed to start USB fuzzer: -22
> > >>> usb-fuzzer-gadget dummy_udc.0: failed to start USB fuzzer: -22
> > >>> usb-fuzzer-gadget dummy_udc.0: failed to start USB fuzzer: -22
> > >>> usb-fuzzer-gadget dummy_udc.0: failed to start USB fuzzer: -22
> > >>> usb-fuzzer-gadget dummy_udc.0: failed to start USB fuzzer: -22
> > >>> INFO: task kworker/0:2:532 blocked for more than 143 seconds.
> > >>>        Not tainted 5.1.0-rc4-319354-g9a33b36 #3
> > >>> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> > >>> kworker/0:2     D26656   532      2 0x80000000
> > >>> Workqueue: usb_hub_wq hub_event
> > >>> Call Trace:
> > >>>   schedule+0x8f/0x180 kernel/sched/core.c:3562
> > >>>   usb_kill_urb drivers/usb/core/urb.c:695 [inline]
> > >>>   usb_kill_urb+0x22a/0x2c0 drivers/usb/core/urb.c:687
> > >>>   usb_start_wait_urb+0x257/0x4d0 drivers/usb/core/message.c:63
> > >>>   usb_internal_control_msg drivers/usb/core/message.c:101 [inline]
> > >>>   usb_control_msg+0x321/0x4a0 drivers/usb/core/message.c:152
> > >>
> > >> It looks like something is stuck waiting for usb_kill_urb() to finish.
> > >> But what happened before that?
> > >
> > > This crash is somewhat special. It happens quite often during USB
> > > fuzzing, but at the same time it's a hang, which makes it a bit harder
> > > debug. I initially thought that is somehow related to my custom USB
> > > fuzzing kernel patches, but then I saw that someone else hit this
> > > issue while doing USB fuzzing in a completely different way that
> > > doesn't require kernel modifications. So it might be an actual issue
> > > in the kernel.
> > >
> > > The full console output is provided by the syzbot, but I guess it's
> > > not very useful in this case. I've just made sure that this issue is
> > > manually reproducible, so we can easily retest it with debug patches
> > > (syzbot should be also able to do that via the syz test command). Or
> > > is there a way to turn on some verbose mode to see some USB debug
> > > messages?
> > >
> > >>
> > >> I can't tell from the reproducer source, because it uses a bunch of
> > >> special stuff you added in your usb-fuzzer tree.
> > >>
> > >> Alan Stern
> > >>
> > >
> > > I understand, for now I guess the simpler way to debug this is to run
> > > the reproducer. I'll write you and Greg a separate email regarding all
> > > that special stuff that I added.
> > >
> >
> > Hi Andrey,
> >
> > Please, CC me on that email too.
>
> Please cc: all of linux-usb@...r.kernel.org, no need to keep anything
> private.

Sure!

>
> thanks,
>
> greg k-h
>

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