linux-kernel - Re: [PATCH net] virtio_net: adjust the execution order of function `virtnet

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Message-Id: <20250814070821.1792157-1-junnan01.wu@samsung.com>
Date: Thu, 14 Aug 2025 15:08:21 +0800
From: Junnan Wu <junnan01.wu@...sung.com>
To: jasowang@...hat.com
Cc: andrew+netdev@...n.ch, davem@...emloft.net, edumazet@...gle.com,
	eperezma@...hat.com, junnan01.wu@...sung.com, kuba@...nel.org,
	lei19.wang@...sung.com, linux-kernel@...r.kernel.org, mst@...hat.com,
	netdev@...r.kernel.org, pabeni@...hat.com, q1.huang@...sung.com,
	virtualization@...ts.linux.dev, xuanzhuo@...ux.alibaba.com,
	ying123.xu@...sung.com
Subject: Re: [PATCH net] virtio_net: adjust the execution order of function
 `virtnet_close` during freeze

On Thu, 14 Aug 2025 14:49:06 +0800 Jason Wang wrote:
> On Thu, Aug 14, 2025 at 2:44 PM Junnan Wu <junnan01.wu@...sung.com> wrote:
> >
> > On Thu, 14 Aug 2025 12:01:18 +0800 Jason Wang wrote:
> > > On Thu, Aug 14, 2025 at 10:36 AM Junnan Wu <junnan01.wu@...sung.com> wrote:
> > > >
> > > > On Wed, 13 Aug 2025 17:23:07 -0700 Jakub Kicinski wrote:
> > > > > Sounds like a fix people may want to backport. Could you repost with
> > > > > an appropriate Fixes tag added, pointing to the earliest commit where
> > > > > the problem can be observed?
> > > >
> > > > This issue is caused by commit "7b0411ef4aa69c9256d6a2c289d0a2b320414633"
> > > > After this patch, during `virtnet_poll`, function `virtnet_poll_cleantx`
> > > > will be invoked, which will wakeup tx queue and clear queue state.
> > > > If you agree with it, I will repost with this Fixes tag later.
> > > >
> > > > Fixes: 7b0411ef4aa6 ("virtio-net: clean tx descriptors from rx napi")
> > >
> > > Could you please explain why it is specific to RX NAPI but not TX?
> > >
> > > Thanks
> >
> > This issue appears in suspend flow, if a TCP connection in host VM is still
> > sending packet before driver suspend is completed, it will tigger RX napi schedule,
> > Finally "use after free" happens when tcp ack timer is up.
> >
> > And in suspend flow, the action to send packet is already stopped in guest VM,
> 
> The TX interrupt and NAPI is not disabled yet. Or anything I miss here?

When system suspends, the userspace progress which based on virtio_net
will be freezed firstly, and then driver suspend callback executes.
so though TX interrupt and NAPI is not disabled at that time, it will also not be scheduled.