linux-kernel - Re: [REGRESSION][v6.8-rc1] virtio-pci: Introduce admin virtqueue

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Date: Wed, 8 May 2024 11:33:53 +0800
From: Jason Wang <jasowang@...hat.com>
To: Joseph Salisbury <joseph.salisbury@...onical.com>
Cc: feliu@...dia.com, parav@...dia.com, jiri@...dia.com, mst@...hat.com, 
	yishaih@...dia.com, alex.williamson@...hat.com, xuanzhuo@...ux.alibaba.com, 
	virtualization@...ts.linux.dev, linux-kernel@...r.kernel.org, 
	Francis Ginther <francis.ginther@...onical.com>, John Cabaj <john.cabaj@...onical.com>, 
	Catherine Redfield <catherine.redfield@...onical.com>, 
	Ankush Pathak <ankush.pathak@...onical.com>, Chlo Smith <chloe.smith@...onical.com>
Subject: Re: [REGRESSION][v6.8-rc1] virtio-pci: Introduce admin virtqueue

On Sat, May 4, 2024 at 2:10 AM Joseph Salisbury
<joseph.salisbury@...onical.com> wrote:
>
> Hi Feng,
>
> During testing, a kernel bug was identified with the suspend/resume
> functionality on instances running in a public cloud [0].  This bug is a
> regression introduced in v6.8-rc1.  After a kernel bisect, the following
> commit was identified as the cause of the regression:
>
>         fd27ef6b44be  ("virtio-pci: Introduce admin virtqueue")

Have a quick glance at the patch it seems it should not damage the
freeze/restore as it should behave as in the past.

But I found something interesting:

1) assumes 1 admin vq which is not what spec said
2) special function for admin virtqueue during freeze/restore, but it
doesn't do anything special than del_vq()
3) lack real users but I guess e.g the destroy_avq() needs to be
synchronized with the one that is using admin virtqueue

>
> I was hoping to get your feedback, since you are the patch author. Do
> you think gathering any additional data will help diagnose this issue?

Yes, please show us

1) the kernel log here.
2) the features that the device has like
/sys/bus/virtio/devices/virtio0/features

> This commit is depended upon by other virtio commits, so a revert test
> is not really straight forward without reverting all the dependencies.
> Any ideas you have would be greatly appreciated.

Thanks

>
>
> Thanks,
>
> Joe
>
> http://pad.lv/2063315
>