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List:       linux-virtualization
Subject:    Re: INFO: task hung in vhost_net_stop_vq
From:       Dmitry Vyukov via Virtualization <virtualization () lists ! linux-foundation ! org>
Date:       2019-03-26 10:28:18
Message-ID: CACT4Y+Z1s-Lx1UXHKj88kQoOcbiD8gwyuRU3F_+cceP3pzbbrw () mail ! gmail ! com
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On Tue, Mar 26, 2019 at 11:17 AM Jason Wang <jasowang@redhat.com> wrote:
> 
> 
> 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.


Looking at the bisection log, syzbot is able to reproduce this
super-reliably on multiple kernel revisions. Are you sure you are
using the right config/revision? What else can be in play? syzbot uses
VMs. The image is available.


> 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@redhat.com>
> > > 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@syzkaller.appspotmail.com
> > > Fixes: 6b1e6cc7 ("vhost: new device IOTLB API")
> 
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