[PATCH net-next] virtio_net: Fix napi_skb_cache_put warning

Breno Leitao
2024-07-12T11:54:22Z

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@kernel.org>
Signed-off-by: Breno Leitao <leitao@debian.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