Re: [PATCH net-next v5 3/4] virtio-net: Map NAPIs to queues

[Joe Damato]

On Wed, Mar 05, 2025 at 06:21:18PM -0800, Jakub Kicinski wrote:
> On Wed, 5 Mar 2025 17:42:35 -0800 Joe Damato wrote:
> > Two spots that come to mind are:
> >  - in virtnet_probe where all the other netdev ops are plumbed
> >    through, or
> >  - above virtnet_disable_queue_pair which I assume a future queue
> >    API implementor would need to call for ndo_queue_stop
> 
> I'd put it next to some call which will have to be inspected.
> Normally we change napi_disable() to napi_disable_locked()
> for drivers using the instance lock, so maybe on the napi_disable()
> line in the refill? 

Sure, that seems reasonable to me.

Does this comment seem reasonable? I tried to distill what you said
in your previous message (thanks for the guidance, btw):

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index d6c8fe670005..fe5f6313d422 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -2883,6 +2883,18 @@ static void refill_work(struct work_struct *work)
        for (i = 0; i < vi->curr_queue_pairs; i++) {
                struct receive_queue *rq = &vi->rq[i];

+               /*
+                * When queue API support is added in the future and the call
+                * below becomes napi_disable_locked, this driver will need to
+                * be refactored.
+                *
+                * One possible solution would be to:
+                *   - cancel refill_work with cancel_delayed_work (note: non-sync)
+                *   - cancel refill_work with cancel_delayed_work_sync in
+                *     virtnet_remove after the netdev is unregistered
+                *   - wrap all of the work in a lock (perhaps vi->refill_lock?)
+                *   - check netif_running() and return early to avoid a race
+                */