Re: [PATCH] virtio-net: disable delayed refill when pausing rx

[Bui Quang Minh]

On 4/8/25 14:34, Jason Wang wrote:
> On Mon, Apr 7, 2025 at 10:27 AM Bui Quang Minh <minhquangbui99@xxxxxxxxx> wrote:
> > On 4/7/25 08:03, Xuan Zhuo wrote:
> > > On Fri,  4 Apr 2025 16:39:03 +0700, Bui Quang Minh <minhquangbui99@xxxxxxxxx> wrote:
> > > > When pausing rx (e.g. set up xdp, xsk pool, rx resize), we call
> > > > napi_disable() on the receive queue's napi. In delayed refill_work, it
> > > > also calls napi_disable() on the receive queue's napi. This can leads to
> > > > deadlock when napi_disable() is called on an already disabled napi. This
> > > > scenario can be reproducible by binding a XDP socket to virtio-net
> > > > interface without setting up the fill ring. As a result, try_fill_recv
> > > > will fail until the fill ring is set up and refill_work is scheduled.
> > > So, what is the problem? The refill_work is waiting? As I know, that thread
> > > will sleep some time, so the cpu can do other work.
> > When napi_disable is called on an already disabled napi, it will sleep
> > in napi_disable_locked while still holding the netdev_lock. As a result,
> > later napi_enable gets stuck too as it cannot acquire the netdev_lock.
> > This leads to refill_work and the pause-then-resume tx are stuck altogether.
> This needs to be added to the chagelog. And it looks like this is a fix for
>
> commit 413f0271f3966e0c73d4937963f19335af19e628
> Author: Jakub Kicinski <kuba@xxxxxxxxxx>
> Date:   Tue Jan 14 19:53:14 2025 -0800
>
>      net: protect NAPI enablement with netdev_lock()
>
> ?

I'm not aware of this, will update the fix tags in the next patch.

> I wonder if it's simpler to just hold the netdev lock in resize or xsk
> binding instead of this.

That looks cleaner, let me try that approach.

Thanks,
Quang Minh