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

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Message-ID: <Z8h9IKvGh4z8h35Y@LQ3V64L9R2>
Date: Wed, 5 Mar 2025 08:34:40 -0800
From: Joe Damato <jdamato@...tly.com>
To: Jason Wang <jasowang@...hat.com>
Cc: Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
	mkarsten@...terloo.ca, gerhard@...leder-embedded.com,
	xuanzhuo@...ux.alibaba.com, mst@...hat.com, leiyang@...hat.com,
	Eugenio Pérez <eperezma@...hat.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	"open list:VIRTIO CORE AND NET DRIVERS" <virtualization@...ts.linux.dev>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next v5 3/4] virtio-net: Map NAPIs to queues

On Wed, Mar 05, 2025 at 01:11:55PM +0800, Jason Wang wrote:
> On Tue, Mar 4, 2025 at 11:09 PM Joe Damato <jdamato@...tly.com> wrote:
> >
> > On Mon, Mar 03, 2025 at 04:03:55PM -0800, Jakub Kicinski wrote:
> > > On Mon, 3 Mar 2025 13:33:10 -0500 Joe Damato wrote:

[...]

> > > Middle ground would be to do what you suggested above and just leave
> > > a well worded comment somewhere that will show up in diffs adding queue
> > > API support?
> >
> > Jason, Michael, et. al.:  what do you think ? I don't want to spin
> > up a v6 if you are opposed to proceeding this way. Please let me
> > know.
> >
> 
> Maybe, but need to make sure there's no use-after-free (etc.
> virtnet_close() has several callers).

Sorry, I think I am missing something. Can you say more?

I was asking: if I add the following diff below to patch 3, will
that be acceptable for you as a middle ground until a more idiomatic
implementation can be done ?

Since this diff leaves refill_work as it functioned before, it
avoids the problem Jakub pointed out and shouldn't introduce any
bugs since refill_work isn't changing from the original
implementation ?

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 76dcd65ec0f2..d6c8fe670005 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -2883,15 +2883,9 @@ static void refill_work(struct work_struct *work)
        for (i = 0; i < vi->curr_queue_pairs; i++) {
                struct receive_queue *rq = &vi->rq[i];

-               rtnl_lock();
-               virtnet_napi_disable(rq);
-               rtnl_unlock();
-
+               napi_disable(&rq->napi);
                still_empty = !try_fill_recv(vi, rq, GFP_KERNEL);
-
-               rtnl_lock();
-               virtnet_napi_enable(rq);
-               rtnl_unlock();
+               virtnet_napi_do_enable(rq->vq, &rq->napi);

                /* In theory, this can happen: if we don't get any buffers in
                 * we will *never* try to fill again.