virtio_net: mergeable xdp: put old page immediately

In the xdp implementation of virtio-net mergeable, it always checks
whether two page is used and a page is selected to release. This is
complicated for the processing of action, and be careful.

In the entire process, we have such principles:
* If xdp_page is used (PASS, TX, Redirect), then we release the old
  page.
* If it is a drop case, we will release two. The old page obtained from
  buf is release inside err_xdp, and xdp_page needs be relased by us.

But in fact, when we allocate a new page, we can release the old page
immediately. Then just one is using, we just need to release the new
page for drop case. On the drop path, err_xdp will release the variable
"page", so we only need to let "page" point to the new xdp_page in
advance.

Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index a12ae26..e9ee4fd 100644 (file)
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1249,6 +1249,9 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
                        if (!xdp_page)
                                goto err_xdp;
                        offset = VIRTIO_XDP_HEADROOM;
+
+                       put_page(page);
+                       page = xdp_page;
                } else if (unlikely(headroom < virtnet_get_headroom(vi))) {
                        xdp_room = SKB_DATA_ALIGN(VIRTIO_XDP_HEADROOM +
                                                  sizeof(struct skb_shared_info));
@@ -1263,11 +1266,12 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
                               page_address(page) + offset, len);
                        frame_sz = PAGE_SIZE;
                        offset = VIRTIO_XDP_HEADROOM;
-               } else {
-                       xdp_page = page;
+
+                       put_page(page);
+                       page = xdp_page;
                }
 
-               data = page_address(xdp_page) + offset;
+               data = page_address(page) + offset;
                err = virtnet_build_xdp_buff_mrg(dev, vi, rq, &xdp, data, len, frame_sz,
                                                 &num_buf, &xdp_frags_truesz, stats);
                if (unlikely(err))
@@ -1282,8 +1286,6 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
                        if (unlikely(!head_skb))
                                goto err_xdp_frags;
 
-                       if (unlikely(xdp_page != page))
-                               put_page(page);
                        rcu_read_unlock();
                        return head_skb;
                case XDP_TX:
@@ -1301,8 +1303,6 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
                                goto err_xdp_frags;
                        }
                        *xdp_xmit |= VIRTIO_XDP_TX;
-                       if (unlikely(xdp_page != page))
-                               put_page(page);
                        rcu_read_unlock();
                        goto xdp_xmit;
                case XDP_REDIRECT:
@@ -1311,8 +1311,6 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
                        if (err)
                                goto err_xdp_frags;
                        *xdp_xmit |= VIRTIO_XDP_REDIR;
-                       if (unlikely(xdp_page != page))
-                               put_page(page);
                        rcu_read_unlock();
                        goto xdp_xmit;
                default:
@@ -1325,9 +1323,6 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
                        goto err_xdp_frags;
                }
 err_xdp_frags:
-               if (unlikely(xdp_page != page))
-                       __free_pages(xdp_page, 0);
-
                if (xdp_buff_has_frags(&xdp)) {
                        shinfo = xdp_get_shared_info_from_buff(&xdp);
                        for (i = 0; i < shinfo->nr_frags; i++) {