linux-kernel - Re: [syzbot] [kvm?] [net?] [virt?] INFO: task hung in __vhost_worker

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Message-ID: <02862261-b7cf-44c1-8437-5e128cfd1201@oracle.com>
Date: Mon, 19 Aug 2024 10:19:44 -0500
From: Mike Christie <michael.christie@...cle.com>
To: "Michael S. Tsirkin" <mst@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Cc: syzbot <syzbot+7f3bbe59e8dd2328a990@...kaller.appspotmail.com>,
        eperezma@...hat.com, jasowang@...hat.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        syzkaller-bugs@...glegroups.com, virtualization@...ts.linux.dev,
        oleg@...hat.com, ebiederm@...ssion.com, sgarzare@...hat.com,
        stefanha@...hat.com, brauner@...nel.org
Subject: Re: [syzbot] [kvm?] [net?] [virt?] INFO: task hung in
 __vhost_worker_flush

On 8/16/24 1:17 PM, Michael S. Tsirkin wrote:
> On Fri, Aug 16, 2024 at 11:10:32AM -0700, Sean Christopherson wrote:
>> On Fri, Aug 16, 2024, syzbot wrote:
>>>> On Wed, May 29, 2024, syzbot wrote:
>>>>> Hello,
>>>>>
>>>>> syzbot found the following issue on:
>>>>>
>>>>> HEAD commit:    9b62e02e6336 Merge tag 'mm-hotfixes-stable-2024-05-25-09-1..
>>>>> git tree:       upstream
>>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=16cb0eec980000
>>>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=3e73beba72b96506
>>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=7f3bbe59e8dd2328a990
>>>>> compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
>>>>>
>>>>> Unfortunately, I don't have any reproducer for this issue yet.
>>>>>
>>>>> Downloadable assets:
>>>>> disk image: https://storage.googleapis.com/syzbot-assets/61b507f6e56c/disk-9b62e02e.raw.xz
>>>>> vmlinux: https://storage.googleapis.com/syzbot-assets/6991f1313243/vmlinux-9b62e02e.xz
>>>>> kernel image: https://storage.googleapis.com/syzbot-assets/65f88b96d046/bzImage-9b62e02e.xz
>>>>>
>>>>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>>>>> Reported-by: syzbot+7f3bbe59e8dd2328a990@...kaller.appspotmail.com
>>>>
>>>> #syz unset kvm
>>>
>>> The following labels did not exist: kvm
>>
>> Hrm, looks like there's no unset for a single subsytem, so:
>>
>> #syz set subsystems: net,virt
> 
> Must be this patchset:
> 
> https://lore.kernel.org/all/20240316004707.45557-1-michael.christie@oracle.com/
> 
> but I don't see anything obvious there to trigger it, and it's not
> reproducible yet...
> 

Sorry, I missed the original post from May.

I'm trying to replicate it now, but am not seeing it.

The only time I've seen something similar is when the flush is actually waiting
for a work item to complete, but I don't think the sysbot tests that for vsock.
So, I think I'm hitting a race that I'm just not seeing yet. I'm just getting
back from vacation, and will do some more testing/review this week.