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Date:   Mon, 15 Apr 2019 21:00:54 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Andrey Konovalov <andreyknvl@...gle.com>
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 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.

thanks,

greg k-h

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