tuntap: tweak on the path of skb XDP case in tun_build_skb()

If we're sure not to go native XDP, there's no need for several things
like bh and rcu stuffs. So this patch introduces a helper to build skb
and hold page refcnt. When we found we will go through skb path, build
skb directly.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 257cf73..946c614 100644 (file)
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1635,6 +1635,23 @@ static bool tun_can_build_skb(struct tun_struct *tun, struct tun_file *tfile,
        return true;
 }
 
+static struct sk_buff *__tun_build_skb(struct page_frag *alloc_frag, char *buf,
+                                      int buflen, int len, int pad, int delta)
+{
+       struct sk_buff *skb = build_skb(buf, buflen);
+
+       if (!skb)
+               return ERR_PTR(-ENOMEM);
+
+       skb_reserve(skb, pad - delta);
+       skb_put(skb, len);
+
+       get_page(alloc_frag->page);
+       alloc_frag->offset += buflen;
+
+       return skb;
+}
+
 static struct sk_buff *tun_build_skb(struct tun_struct *tun,
                                     struct tun_file *tfile,
                                     struct iov_iter *from,
@@ -1642,7 +1659,6 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
                                     int len, int *skb_xdp)
 {
        struct page_frag *alloc_frag = &current->task_frag;
-       struct sk_buff *skb;
        struct bpf_prog *xdp_prog;
        int buflen = SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
        unsigned int delta = 0;
@@ -1672,10 +1688,12 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
         * of xdp_prog above, this should be rare and for simplicity
         * we do XDP on skb in case the headroom is not enough.
         */
-       if (hdr->gso_type || !xdp_prog)
+       if (hdr->gso_type || !xdp_prog) {
                *skb_xdp = 1;
-       else
-               *skb_xdp = 0;
+               return __tun_build_skb(alloc_frag, buf, buflen, len, pad, delta);
+       }
+
+       *skb_xdp = 0;
 
        local_bh_disable();
        rcu_read_lock();
@@ -1719,22 +1737,13 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
                        trace_xdp_exception(tun->dev, xdp_prog, act);
                        /* fall through */
                case XDP_DROP:
-                       goto err_xdp;
+                       goto out;
                }
        }
        rcu_read_unlock();
        local_bh_enable();
 
-       skb = build_skb(buf, buflen);
-       if (!skb)
-               return ERR_PTR(-ENOMEM);
-
-       skb_reserve(skb, pad - delta);
-       skb_put(skb, len);
-       get_page(alloc_frag->page);
-       alloc_frag->offset += buflen;
-
-       return skb;
+       return __tun_build_skb(alloc_frag, buf, buflen, len, pad, delta);
 
 err_redirect:
        put_page(alloc_frag->page);