netdev - [PATCH net-next] virtio_net: Fix napi_skb_cache

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Message-ID: <20240712115325.54175-1-leitao@debian.org>
Date: Fri, 12 Jul 2024 04:53:25 -0700
From: Breno Leitao <leitao@...ian.org>
To: "Michael S. Tsirkin" <mst@...hat.com>,
	Jason Wang <jasowang@...hat.com>,
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
	Eugenio Pérez <eperezma@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>
Cc: rbc@...a.com,
	horms@...nel.org,
	virtualization@...ts.linux.dev (open list:VIRTIO CORE AND NET DRIVERS),
	netdev@...r.kernel.org (open list:NETWORKING DRIVERS),
	linux-kernel@...r.kernel.org (open list)
Subject: [PATCH net-next] virtio_net: Fix napi_skb_cache_put warning

After the commit bdacf3e34945 ("net: Use nested-BH locking for
napi_alloc_cache.") was merged, the following warning began to appear:

	 WARNING: CPU: 5 PID: 1 at net/core/skbuff.c:1451 napi_skb_cache_put+0x82/0x4b0

	  __warn+0x12f/0x340
	  napi_skb_cache_put+0x82/0x4b0
	  napi_skb_cache_put+0x82/0x4b0
	  report_bug+0x165/0x370
	  handle_bug+0x3d/0x80
	  exc_invalid_op+0x1a/0x50
	  asm_exc_invalid_op+0x1a/0x20
	  __free_old_xmit+0x1c8/0x510
	  napi_skb_cache_put+0x82/0x4b0
	  __free_old_xmit+0x1c8/0x510
	  __free_old_xmit+0x1c8/0x510
	  __pfx___free_old_xmit+0x10/0x10

The issue arises because virtio is assuming it's running in NAPI context
even when it's not, such as in the netpoll case.

To resolve this, modify virtnet_poll_tx() to only set NAPI when budget
is available. Same for virtnet_poll_cleantx(), which always assumed that
it was in a NAPI context.

Fixes: df133f3f9625 ("virtio_net: bulk free tx skbs")
Suggested-by: Jakub Kicinski <kuba@...nel.org>
Signed-off-by: Breno Leitao <leitao@...ian.org>
---
 drivers/net/virtio_net.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 0b4747e81464..fb1331827308 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -2341,7 +2341,7 @@ static int virtnet_receive(struct receive_queue *rq, int budget,
 	return packets;
 }
 
-static void virtnet_poll_cleantx(struct receive_queue *rq)
+static void virtnet_poll_cleantx(struct receive_queue *rq, int budget)
 {
 	struct virtnet_info *vi = rq->vq->vdev->priv;
 	unsigned int index = vq2rxq(rq->vq);
@@ -2359,7 +2359,7 @@ static void virtnet_poll_cleantx(struct receive_queue *rq)
 
 		do {
 			virtqueue_disable_cb(sq->vq);
-			free_old_xmit(sq, txq, true);
+			free_old_xmit(sq, txq, !!budget);
 		} while (unlikely(!virtqueue_enable_cb_delayed(sq->vq)));
 
 		if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS) {
@@ -2404,7 +2404,7 @@ static int virtnet_poll(struct napi_struct *napi, int budget)
 	unsigned int xdp_xmit = 0;
 	bool napi_complete;
 
-	virtnet_poll_cleantx(rq);
+	virtnet_poll_cleantx(rq, budget);
 
 	received = virtnet_receive(rq, budget, &xdp_xmit);
 	rq->packets_in_napi += received;
@@ -2526,7 +2526,7 @@ static int virtnet_poll_tx(struct napi_struct *napi, int budget)
 	txq = netdev_get_tx_queue(vi->dev, index);
 	__netif_tx_lock(txq, raw_smp_processor_id());
 	virtqueue_disable_cb(sq->vq);
-	free_old_xmit(sq, txq, true);
+	free_old_xmit(sq, txq, !!budget);
 
 	if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS) {
 		if (netif_tx_queue_stopped(txq)) {
-- 
2.43.0