On Fri, Jul 12, 2024 at 04:53:25AM -0700, Breno Leitao wrote:
> 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@xxxxxxxxxx>
> Signed-off-by: Breno Leitao <leitao@xxxxxxxxxx>
Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
though I'm not sure I understand the connection with bdacf3e34945.
> ---
> 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
