netdev - [PATCH net-next 03/10] ipv6: np->rxpmtu race annotation

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Message-ID: <20250916160951.541279-4-edumazet@google.com>
Date: Tue, 16 Sep 2025 16:09:44 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: Simon Horman <horms@...nel.org>, Willem de Bruijn <willemb@...gle.com>, 
	Kuniyuki Iwashima <kuniyu@...gle.com>, David Ahern <dsahern@...nel.org>, netdev@...r.kernel.org, 
	eric.dumazet@...il.com, Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net-next 03/10] ipv6: np->rxpmtu race annotation

Add READ_ONCE() annotations because np->rxpmtu can be changed
while udpv6_recvmsg() and rawv6_recvmsg() read it.

Since this is a very rarely used feature, and that udpv6_recvmsg()
and rawv6_recvmsg() read np->rxopt anyway, change the test order
so that np->rxpmtu does not need to be in a hot cache line.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/ipv6/raw.c | 2 +-
 net/ipv6/udp.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/ipv6/raw.c b/net/ipv6/raw.c
index 4ae07a67b4d4f1be6730c252d246e79ff9c73d4c..e369f54844dd9456a819db77435eaef33d162932 100644
--- a/net/ipv6/raw.c
+++ b/net/ipv6/raw.c
@@ -445,7 +445,7 @@ static int rawv6_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 	if (flags & MSG_ERRQUEUE)
 		return ipv6_recv_error(sk, msg, len, addr_len);
 
-	if (np->rxpmtu && np->rxopt.bits.rxpmtu)
+	if (np->rxopt.bits.rxpmtu && READ_ONCE(np->rxpmtu))
 		return ipv6_recv_rxpmtu(sk, msg, len, addr_len);
 
 	skb = skb_recv_datagram(sk, flags, &err);
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index b70369f3cd3223cfde07556b1cb1636e8bc78d49..e87d0ef861f88af3ff7bf9dd5045c4d4601036e3 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -479,7 +479,7 @@ int udpv6_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 	if (flags & MSG_ERRQUEUE)
 		return ipv6_recv_error(sk, msg, len, addr_len);
 
-	if (np->rxpmtu && np->rxopt.bits.rxpmtu)
+	if (np->rxopt.bits.rxpmtu && READ_ONCE(np->rxpmtu))
 		return ipv6_recv_rxpmtu(sk, msg, len, addr_len);
 
 try_again:
-- 
2.51.0.384.g4c02a37b29-goog