From: Liu Jian <liujian56@huawei.com>
Date: Wed, 27 Apr 2022 19:51:50 +0800
Subject: bpf, sockmap: Call skb_linearize only when required in
 sk_psock_skb_ingress_enqueue
Patch-mainline: v5.19-rc1
Git-commit: 3527bfe6a92d940abfca87929207e734039f496b
References: jsc#PED-1377

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
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
---
 net/core/skmsg.c |   22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

--- a/net/core/skmsg.c
+++ b/net/core/skmsg.c
@@ -524,16 +524,20 @@ static int sk_psock_skb_ingress_enqueue(
 {
 	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;