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Date:   Fri, 12 Apr 2019 15:46:25 -0400 (EDT)
From:   Alan Stern <stern@rowland.harvard.edu>
To:     andreyknvl@google.com
cc:     gregkh@linuxfoundation.org, <gustavo@embeddedor.com>,
        Kernel development list <linux-kernel@vger.kernel.org>,
        USB list <linux-usb@vger.kernel.org>,
        <syzkaller-bugs@googlegroups.com>
Subject: Re: INFO: task hung in usb_kill_urb
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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?

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