Re: INFO: task hung in vhost_net_stop_vq

[Jason Wang]

On 2019/3/25 äå10:02, 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 <jasowang@xxxxxxxxxx>
> > 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: syzbot+d21e6e297322a900c128@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Fixes: 6b1e6cc7 ("vhost: new device IOTLB API")