bpf, sockmap: Call skb_linearize only when required in sk_psock_skb_ingress_enqueue

The skb_to_sgvec fails only when the number of frag_list and frags
exceeds MAX_MSG_FRAGS. Therefore, we can call skb_linearize only
when the conversion fails.

Signed-off-by: Liu Jian <liujian56@huawei.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20220427115150.210213-1-liujian56@huawei.com

diff --git a/net/core/skmsg.c b/net/core/skmsg.c
index cc381165ea0809b07b6dee799db8cc58e3eb8ba9..22b983ade0e7da7fcbf54e91b326b61bb23b1532 100644 (file)
--- a/net/core/skmsg.c
+++ b/net/core/skmsg.c
@@ -524,16 +524,20 @@ static int sk_psock_skb_ingress_enqueue(struct sk_buff *skb,
 {
        int num_sge, copied;
 
-       /* skb linearize may fail with ENOMEM, but lets simply try again
-        * later if this happens. Under memory pressure we don't want to
-        * drop the skb. We need to linearize the skb so that the mapping
-        * in skb_to_sgvec can not error.
-        */
-       if (skb_linearize(skb))
-               return -EAGAIN;
        num_sge = skb_to_sgvec(skb, msg->sg.data, off, len);
-       if (unlikely(num_sge < 0))
-               return num_sge;
+       if (num_sge < 0) {
+               /* skb linearize may fail with ENOMEM, but lets simply try again
+                * later if this happens. Under memory pressure we don't want to
+                * drop the skb. We need to linearize the skb so that the mapping
+                * in skb_to_sgvec can not error.
+                */
+               if (skb_linearize(skb))
+                       return -EAGAIN;
+
+               num_sge = skb_to_sgvec(skb, msg->sg.data, off, len);
+               if (unlikely(num_sge < 0))
+                       return num_sge;
+       }
 
        copied = len;
        msg->sg.start = 0;