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Subject: Re: INFO: task hung in usb_kill_urb
To:     Andrey Konovalov <andreyknvl@google.com>,
        Alan Stern <stern@rowland.harvard.edu>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Kernel development list <linux-kernel@vger.kernel.org>,
        USB list <linux-usb@vger.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>
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From:   "Gustavo A. R. Silva" <gustavo@embeddedor.com>
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Message-ID: <52ac871b-ac61-432e-3a85-47b8e97233d2@embeddedor.com>
Date:   Mon, 15 Apr 2019 13:39:57 -0500
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On 4/15/19 12:48 PM, Andrey Konovalov wrote:
> On Fri, Apr 12, 2019 at 9:46 PM Alan Stern <stern@rowland.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@syzkaller.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.

Thanks
--
Gustavo