# Re: INFO: task hung in vhost\_net\_stop\_vq

- From: Jason Wang \<hidden\>
- Date: 2019-03-26 10:17:35 
- List: netdev
- Page: https://ratatoskr.run/netdev/2019/03/5550326
- Thread: https://ratatoskr.run/kvm/2018/11/5449727/t.md

```text

On 2019/3/25 下午10:02, Michael S. Tsirkin wrote:
> Looks like more iotlb locking mess?


Looking at the calltrace:

[  221.743675] =============================================
[  221.744297] [ INFO: possible recursive locking detected ]
[  221.744944] 4.7.0+ #1 Not tainted
[  221.745326] ---------------------------------------------
[  221.746128] syz-executor1/6823 is trying to acquire lock:
[  221.746737]  (&vq->mutex){+.+...}, at: [<ffffffff84484b70>] vhost_process_iotlb_msg+0xe0/0x9e0
[  221.747789]
[  221.747789] but task is already holding lock:
[  221.748470]  (&vq->mutex){+.+...}, at: [<ffffffff84484b70>] vhost_process_iotlb_msg+0xe0/0x9e0
[  221.749535]
[  221.749535] other info that might help us debug this:
[  221.750280]  Possible unsafe locking scenario:
[  221.750280]
[  221.750946]        CPU0
[  221.751232]        ----
[  221.751523]   lock(&vq->mutex);
[  221.751922]   lock(&vq->mutex);
[  221.752339]
[  221.752339]  *** DEADLOCK ***
[  221.752339]

I could not think of a path that can hit this. And I could not reproduce with the reproducer in the link in net-next.

Thanks


>
> On Tue, Mar 19, 2019 at 10:21:00PM -0700, syzbot wrote:
>> syzbot has bisected this bug to:
>>
>> commit 6b1e6cc7855b09a0a9bfa1d9f30172ba366f161c
>> Author: Jason Wang [ref]
>> Date:   Thu Jun 23 06:04:32 2016 +0000
>>
>>      vhost: new device IOTLB API
>>
>> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1486ad27200000
>> start commit:   6b1e6cc7 vhost: new device IOTLB API
>> git tree:       upstream
>> final crash:    https://syzkaller.appspot.com/x/report.txt?x=1686ad27200000
>> console output: https://syzkaller.appspot.com/x/log.txt?x=1286ad27200000
>> kernel config:  https://syzkaller.appspot.com/x/.config?x=c94f9f0c0363db4b
>> dashboard link: https://syzkaller.appspot.com/bug?extid=d21e6e297322a900c128
>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=141db34d400000
>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=108ef293400000
>>
>> Reported-by: <redacted>
>> Fixes: 6b1e6cc7 ("vhost: new device IOTLB API")
```