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From:   Vasily Averin <vvs@virtuozzo.com>
Subject: [PATCH IPV6 v2 2/4] ipv6: use new helper skb_expand_head() in
 ip6_xmit()
To:     "David S. Miller" <davem@davemloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        David Ahern <dsahern@kernel.org>,
        Jakub Kicinski <kuba@kernel.org>,
        Eric Dumazet <eric.dumazet@gmail.com>
Cc:     netdev@vger.kernel.org, linux-kernel@vger.kernel.org
References: <1cbf3c7b-455e-f3a5-cc2c-c18ce8be4ce1@gmail.com>
 <cover.1625818825.git.vvs@virtuozzo.com>
Message-ID: <64dd5cd2-cfd9-60b3-ae1c-39470ff75256@virtuozzo.com>
Date:   Fri, 9 Jul 2021 12:04:54 +0300
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By this way can be changed:
pptp_xmit
vrf_finish_output
ax25_transmit_buffer
ax25_rt_build_path
bpf_out_neigh_v6
bpf_out_neigh_v4
ip_finish_output2
ip6_tnl_xmit
ipip6_tunnel_xmit
ip_vs_prepare_tunneled_skb

Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
---
 net/ipv6/ip6_output.c | 16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)

diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 6c5f85f..9418802 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -278,25 +278,21 @@ int ip6_xmit(const struct sock *sk, struct sk_buff *skb, struct flowi6 *fl6,
 	struct ipv6hdr *hdr;
 	u8  proto = fl6->flowi6_proto;
 	int seg_len = skb->len;
-	int hlimit = -1;
+	int delta, hlimit = -1;
 	u32 mtu;
 
 	head_room = sizeof(struct ipv6hdr) + LL_RESERVED_SPACE(dst->dev);
 	if (opt)
 		head_room += opt->opt_nflen + opt->opt_flen;
 
-	if (unlikely(skb_headroom(skb) < head_room)) {
-		struct sk_buff *skb2 = skb_realloc_headroom(skb, head_room);
-		if (!skb2) {
-			IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),
+	delta = head_room - skb_headroom(skb);
+	if (unlikely(delta > 0)) {
+		skb = skb_expand_head(skb, delta);
+		if (!skb) {
+			IP6_INC_STATS(net, ip6_dst_idev(dst),
 				      IPSTATS_MIB_OUTDISCARDS);
-			kfree_skb(skb);
 			return -ENOBUFS;
 		}
-		if (skb->sk)
-			skb_set_owner_w(skb2, skb->sk);
-		consume_skb(skb);
-		skb = skb2;
 	}
 
 	if (opt) {
-- 
1.8.3.1