From: Sasha Levin <sashal@kernel.org>
To: stable@vger.kernel.org
Cc: Eric Dumazet <edumazet@google.com>,
Kuniyuki Iwashima <kuniyu@google.com>,
Jakub Kicinski <kuba@kernel.org>, Sasha Levin <sashal@kernel.org>
Subject: [PATCH 6.6.y 4/5] ipv4: use dst4_mtu() instead of dst_mtu()
Date: Tue, 1 Sep 2026 10:18:03 -0400 [thread overview]
Message-ID: <20260901141804.1031618-4-sashal@kernel.org> (raw)
In-Reply-To: <20260901141804.1031618-1-sashal@kernel.org>
From: Eric Dumazet <edumazet@google.com>
[ Upstream commit fe8570186f100b6cc499b2f7705946baf1388cde ]
When we expect an IPv4 dst, use dst4_mtu() instead of dst_mtu()
to save some code space.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260130210303.3888261-8-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
[ Resolved conflicts in net/ipv4/ip_output.c and net/ipv4/ipmr.c,
caused by unrelated local/upstream divergence unrelated to this
commit's own diff:
- ip_output.c: upstream's pre-image already has
'pmtudisc = READ_ONCE(inet->pmtudisc);' hoisted out of the if
condition in __ip_make_skb() (from a commit not present in this
tree); kept this tree's un-hoisted 'inet->pmtudisc' form and
applied only the dst_mtu() -> dst4_mtu() substitution.
- ipmr.c: this tree already has an extra 'dev = rt->dst.dev;'
line before the MTU check in ipmr_prepare_xmit() that upstream's
pre-image doesn't carry; kept that line and applied only the
dst_mtu() -> dst4_mtu() substitution. ]
Stable-dep-of: 870a9e42ecc6 ("tcp: clamp route advmss to TCP_MIN_MSS")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/ipv4/icmp.c | 2 +-
net/ipv4/ip_output.c | 4 ++--
net/ipv4/ip_sockglue.c | 2 +-
net/ipv4/ipmr.c | 2 +-
net/ipv4/netfilter/nf_reject_ipv4.c | 2 +-
net/ipv4/tcp_ipv4.c | 13 ++++++-------
net/ipv6/sit.c | 2 +-
7 files changed, 13 insertions(+), 14 deletions(-)
diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
index 7c4c7b7fe3846..69cac8b20a217 100644
--- a/net/ipv4/icmp.c
+++ b/net/ipv4/icmp.c
@@ -785,7 +785,7 @@ void __icmp_send(struct sk_buff *skb_in, int type, int code, __be32 info,
/* RFC says return as much as we can without exceeding 576 bytes. */
- room = dst_mtu(&rt->dst);
+ room = dst4_mtu(&rt->dst);
if (room > 576)
room = 576;
room -= sizeof(struct iphdr) + icmp_param.replyopts.opt.opt.optlen;
diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 150cdea8aacbe..9698290ef7293 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1304,7 +1304,7 @@ static int ip_setup_cork(struct sock *sk, struct inet_cork *cork,
return -EFAULT;
cork->fragsize = ip_sk_use_pmtu(sk) ?
- dst_mtu(&rt->dst) : READ_ONCE(rt->dst.dev->mtu);
+ dst4_mtu(&rt->dst) : READ_ONCE(rt->dst.dev->mtu);
if (!inetdev_valid_mtu(cork->fragsize))
return -ENETUNREACH;
@@ -1438,7 +1438,7 @@ struct sk_buff *__ip_make_skb(struct sock *sk,
* locally. */
if (inet->pmtudisc == IP_PMTUDISC_DO ||
inet->pmtudisc == IP_PMTUDISC_PROBE ||
- (skb->len <= dst_mtu(&rt->dst) &&
+ (skb->len <= dst4_mtu(&rt->dst) &&
ip_dont_fragment(sk, &rt->dst)))
df = htons(IP_DF);
diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
index 1a6952921e07b..a5affb6e280ef 100644
--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -1642,7 +1642,7 @@ int do_ip_getsockopt(struct sock *sk, int level, int optname,
val = 0;
dst = sk_dst_get(sk);
if (dst) {
- val = dst_mtu(dst);
+ val = dst4_mtu(dst);
dst_release(dst);
}
if (!val) {
diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index af9412a507cf3..074662e2daed6 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -1895,7 +1895,7 @@ static void ipmr_queue_xmit(struct net *net, struct mr_table *mrt,
dev = rt->dst.dev;
- if (skb->len+encap > dst_mtu(&rt->dst) && (ntohs(iph->frag_off) & IP_DF)) {
+ if (skb->len+encap > dst4_mtu(&rt->dst) && (ntohs(iph->frag_off) & IP_DF)) {
/* Do not fragment multicasts. Alas, IPv4 does not
* allow to send ICMP, so that packets will disappear
* to blackhole.
diff --git a/net/ipv4/netfilter/nf_reject_ipv4.c b/net/ipv4/netfilter/nf_reject_ipv4.c
index 1632cedcd348c..76320f1ba4996 100644
--- a/net/ipv4/netfilter/nf_reject_ipv4.c
+++ b/net/ipv4/netfilter/nf_reject_ipv4.c
@@ -296,7 +296,7 @@ void nf_send_reset(struct net *net, struct sock *sk, struct sk_buff *oldskb,
goto free_nskb;
/* "Never happens" */
- if (nskb->len > dst_mtu(skb_dst(nskb)))
+ if (nskb->len > dst4_mtu(skb_dst(nskb)))
goto free_nskb;
nf_ct_attach(nskb, oldskb);
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 3f9e1cfde0083..97e3ce3e60f98 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -363,7 +363,7 @@ void tcp_v4_mtu_reduced(struct sock *sk)
{
struct inet_sock *inet = inet_sk(sk);
struct dst_entry *dst;
- u32 mtu;
+ u32 mtu, dmtu;
if ((1 << sk->sk_state) & (TCPF_LISTEN | TCPF_CLOSE))
return;
@@ -375,15 +375,14 @@ void tcp_v4_mtu_reduced(struct sock *sk)
/* Something is about to be wrong... Remember soft error
* for the case, if this connection will not able to recover.
*/
- if (mtu < dst_mtu(dst) && ip_dont_fragment(sk, dst))
+ dmtu = dst4_mtu(dst);
+ if (mtu < dmtu && ip_dont_fragment(sk, dst))
WRITE_ONCE(sk->sk_err_soft, EMSGSIZE);
- mtu = dst_mtu(dst);
-
if (inet->pmtudisc != IP_PMTUDISC_DONT &&
ip_sk_accept_pmtu(sk) &&
- inet_csk(sk)->icsk_pmtu_cookie > mtu) {
- tcp_sync_mss(sk, mtu);
+ inet_csk(sk)->icsk_pmtu_cookie > dmtu) {
+ tcp_sync_mss(sk, dmtu);
/* Resend the TCP packet because it's
* clear that the old packet has been
@@ -1624,7 +1623,7 @@ struct sock *tcp_v4_syn_recv_sock(const struct sock *sk, struct sk_buff *skb,
tcp_ca_openreq_child(newsk, dst);
- tcp_sync_mss(newsk, dst_mtu(dst));
+ tcp_sync_mss(newsk, dst4_mtu(dst));
newtp->advmss = tcp_mss_clamp(tcp_sk(sk), dst_metric_advmss(dst));
tcp_initialize_rcv_mss(newsk);
diff --git a/net/ipv6/sit.c b/net/ipv6/sit.c
index ac38d4aa09ddc..b36fc57acf061 100644
--- a/net/ipv6/sit.c
+++ b/net/ipv6/sit.c
@@ -968,7 +968,7 @@ static netdev_tx_t ipip6_tunnel_xmit(struct sk_buff *skb,
iph6 = ipv6_hdr(skb);
if (df) {
- mtu = dst_mtu(&rt->dst) - t_hlen;
+ mtu = dst4_mtu(&rt->dst) - t_hlen;
if (mtu < IPV4_MIN_MTU) {
DEV_STATS_INC(dev, collisions);
--
2.53.0
next prev parent reply other threads:[~2026-09-01 14:18 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-08-31 12:53 FAILED: patch "[PATCH] tcp: clamp route advmss to TCP_MIN_MSS" failed to apply to 6.6-stable tree gregkh
2026-09-01 14:18 ` [PATCH 6.6.y 1/5] ipv6: pass proto by value to ipv6_push_nfrag_opts() and ipv6_push_frag_opts() Sasha Levin
2026-09-01 14:18 ` [PATCH 6.6.y 2/5] inet: add dst4_mtu() and dst6_mtu() helpers Sasha Levin
2026-09-01 14:18 ` [PATCH 6.6.y 3/5] ipv6: use dst6_mtu() instead of dst_mtu() Sasha Levin
2026-09-01 14:18 ` Sasha Levin [this message]
2026-09-01 14:18 ` [PATCH 6.6.y 5/5] tcp: clamp route advmss to TCP_MIN_MSS Sasha Levin
2026-09-30 14:10 ` Greg KH
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