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Date: Tue, 29 Jan 2019 17:51:10 -0500
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
Cc: "David S. Miller" <davem@...emloft.net>,
Jason Wang <jasowang@...hat.com>, netdev@...r.kernel.org,
virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v2 net 7/7] virtio_net: Differentiate sk_buff and
xdp_frame on freeing
On Tue, Jan 29, 2019 at 09:45:59AM +0900, Toshiaki Makita wrote:
> We do not reset or free up unused buffers when enabling/disabling XDP,
> so it can happen that xdp_frames are freed after disabling XDP or
> sk_buffs are freed after enabling XDP on xdp tx queues.
> Thus we need to handle both forms (xdp_frames and sk_buffs) regardless
> of XDP setting.
> One way to trigger this problem is to disable XDP when napi_tx is
> enabled. In that case, virtnet_xdp_set() calls virtnet_napi_enable()
> which kicks NAPI. The NAPI handler will call virtnet_poll_cleantx()
> which invokes free_old_xmit_skbs() for queues which have been used by
> XDP.
>
> Note that even with this change we need to keep skipping
> free_old_xmit_skbs() from NAPI handlers when XDP is enabled, because XDP
> tx queues do not aquire queue locks.
>
> - v2: Use napi_consume_skb() instead of dev_consume_skb_any()
>
> Fixes: 4941d472bf95 ("virtio-net: do not reset during XDP set")
> Signed-off-by: Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
Acked-by: Michael S. Tsirkin <mst@...hat.com>
> ---
> NOTE: Dropped Acked-by because of the v2 change.
>
> drivers/net/virtio_net.c | 54 +++++++++++++++++++++++++++++++++++++-----------
> 1 file changed, 42 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 1d454ce..2594481 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -57,6 +57,8 @@
> #define VIRTIO_XDP_TX BIT(0)
> #define VIRTIO_XDP_REDIR BIT(1)
>
> +#define VIRTIO_XDP_FLAG BIT(0)
> +
> /* RX packet size EWMA. The average packet size is used to determine the packet
> * buffer size when refilling RX rings. As the entire RX ring may be refilled
> * at once, the weight is chosen so that the EWMA will be insensitive to short-
> @@ -252,6 +254,21 @@ struct padded_vnet_hdr {
> char padding[4];
> };
>
> +static bool is_xdp_frame(void *ptr)
> +{
> + return (unsigned long)ptr & VIRTIO_XDP_FLAG;
> +}
> +
> +static void *xdp_to_ptr(struct xdp_frame *ptr)
> +{
> + return (void *)((unsigned long)ptr | VIRTIO_XDP_FLAG);
> +}
> +
> +static struct xdp_frame *ptr_to_xdp(void *ptr)
> +{
> + return (struct xdp_frame *)((unsigned long)ptr & ~VIRTIO_XDP_FLAG);
> +}
> +
> /* Converting between virtqueue no. and kernel tx/rx queue no.
> * 0:rx0 1:tx0 2:rx1 3:tx1 ... 2N:rxN 2N+1:txN 2N+2:cvq
> */
> @@ -462,7 +479,8 @@ static int __virtnet_xdp_xmit_one(struct virtnet_info *vi,
>
> sg_init_one(sq->sg, xdpf->data, xdpf->len);
>
> - err = virtqueue_add_outbuf(sq->vq, sq->sg, 1, xdpf, GFP_ATOMIC);
> + err = virtqueue_add_outbuf(sq->vq, sq->sg, 1, xdp_to_ptr(xdpf),
> + GFP_ATOMIC);
> if (unlikely(err))
> return -ENOSPC; /* Caller handle free/refcnt */
>
> @@ -482,13 +500,13 @@ static int virtnet_xdp_xmit(struct net_device *dev,
> {
> struct virtnet_info *vi = netdev_priv(dev);
> struct receive_queue *rq = vi->rq;
> - struct xdp_frame *xdpf_sent;
> struct bpf_prog *xdp_prog;
> struct send_queue *sq;
> unsigned int len;
> int drops = 0;
> int kicks = 0;
> int ret, err;
> + void *ptr;
> int i;
>
> /* Only allow ndo_xdp_xmit if XDP is loaded on dev, as this
> @@ -507,8 +525,12 @@ static int virtnet_xdp_xmit(struct net_device *dev,
> }
>
> /* Free up any pending old buffers before queueing new ones. */
> - while ((xdpf_sent = virtqueue_get_buf(sq->vq, &len)) != NULL)
> - xdp_return_frame(xdpf_sent);
> + while ((ptr = virtqueue_get_buf(sq->vq, &len)) != NULL) {
> + if (likely(is_xdp_frame(ptr)))
> + xdp_return_frame(ptr_to_xdp(ptr));
> + else
> + napi_consume_skb(ptr, false);
> + }
>
> for (i = 0; i < n; i++) {
> struct xdp_frame *xdpf = frames[i];
> @@ -1329,18 +1351,26 @@ static int virtnet_receive(struct receive_queue *rq, int budget,
>
> static void free_old_xmit_skbs(struct send_queue *sq, bool in_napi)
> {
> - struct sk_buff *skb;
> unsigned int len;
> unsigned int packets = 0;
> unsigned int bytes = 0;
> + void *ptr;
>
> - while ((skb = virtqueue_get_buf(sq->vq, &len)) != NULL) {
> - pr_debug("Sent skb %p\n", skb);
> + while ((ptr = virtqueue_get_buf(sq->vq, &len)) != NULL) {
> + if (likely(!is_xdp_frame(ptr))) {
> + struct sk_buff *skb = ptr;
>
> - bytes += skb->len;
> - packets++;
> + pr_debug("Sent skb %p\n", skb);
>
> - napi_consume_skb(skb, in_napi);
> + bytes += skb->len;
> + napi_consume_skb(skb, in_napi);
> + } else {
> + struct xdp_frame *frame = ptr_to_xdp(ptr);
> +
> + bytes += frame->len;
> + xdp_return_frame(frame);
> + }
> + packets++;
> }
>
> /* Avoid overhead when no packets have been processed
> @@ -2666,10 +2696,10 @@ static void free_unused_bufs(struct virtnet_info *vi)
> for (i = 0; i < vi->max_queue_pairs; i++) {
> struct virtqueue *vq = vi->sq[i].vq;
> while ((buf = virtqueue_detach_unused_buf(vq)) != NULL) {
> - if (!is_xdp_raw_buffer_queue(vi, i))
> + if (!is_xdp_frame(buf))
> dev_kfree_skb(buf);
> else
> - xdp_return_frame(buf);
> + xdp_return_frame(ptr_to_xdp(buf));
> }
> }
>
> --
> 1.8.3.1
>
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