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Date:   Tue, 9 Apr 2019 11:31:44 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        syzbot <syzbot+d21e6e297322a900c128@...kaller.appspotmail.com>,
        KVM list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        virtualization@...ts.linux-foundation.org, weiyj.lk@...il.com
Subject: Re: INFO: task hung in vhost_net_stop_vq


On 2019/3/26 下午6:28, Dmitry Vyukov wrote:
> On Tue, Mar 26, 2019 at 11:17 AM Jason Wang<jasowang@...hat.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.
>
>

Yes, looks like the reason is vhost accept zero size iova range which 
lead a infinite loop when trying to translate iova. Will post a patch to 
fix this.

Thanks

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