netdev - [PATCH bpf-next] bpf, sockmap: Call skb_linearize only when required in sk_psock_skb_ingress

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Date:   Wed, 27 Apr 2022 19:51:50 +0800
From:   Liu Jian <liujian56@...wei.com>
To:     <john.fastabend@...il.com>, <daniel@...earbox.net>,
        <jakub@...udflare.com>, <davem@...emloft.net>, <kuba@...nel.org>,
        <pabeni@...hat.com>, <ast@...nel.org>, <andrii@...nel.org>,
        <kafai@...com>, <songliubraving@...com>, <yhs@...com>,
        <kpsingh@...nel.org>, <netdev@...r.kernel.org>,
        <bpf@...r.kernel.org>
CC:     <liujian56@...wei.com>
Subject: [PATCH bpf-next] 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@...wei.com>
---
 net/core/skmsg.c | 22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/net/core/skmsg.c b/net/core/skmsg.c
index cc381165ea08..22b983ade0e7 100644
--- 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;
-- 
2.17.1