netdev - [PATCH net-next 03/10] tcp: sk->sk_bound_dev_if once in inet_request_bound_dev

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Message-Id: <20220511233757.2001218-4-eric.dumazet@gmail.com>
Date:   Wed, 11 May 2022 16:37:50 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: [PATCH net-next 03/10] tcp: sk->sk_bound_dev_if once in inet_request_bound_dev_if()

From: Eric Dumazet <edumazet@...gle.com>

inet_request_bound_dev_if() reads sk->sk_bound_dev_if twice
while listener socket is not locked.

Another cpu could change this field under us.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 include/net/inet_sock.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/net/inet_sock.h b/include/net/inet_sock.h
index 234d70ae5f4cbdc3b2caaf10df81495439a101a5..c1b5dcd6597c622dfea3d4a646f97c87acb7ea32 100644
--- a/include/net/inet_sock.h
+++ b/include/net/inet_sock.h
@@ -116,14 +116,15 @@ static inline u32 inet_request_mark(const struct sock *sk, struct sk_buff *skb)
 static inline int inet_request_bound_dev_if(const struct sock *sk,
 					    struct sk_buff *skb)
 {
+	int bound_dev_if = READ_ONCE(sk->sk_bound_dev_if);
 #ifdef CONFIG_NET_L3_MASTER_DEV
 	struct net *net = sock_net(sk);
 
-	if (!sk->sk_bound_dev_if && net->ipv4.sysctl_tcp_l3mdev_accept)
+	if (!bound_dev_if && net->ipv4.sysctl_tcp_l3mdev_accept)
 		return l3mdev_master_ifindex_by_index(net, skb->skb_iif);
 #endif
 
-	return sk->sk_bound_dev_if;
+	return bound_dev_if;
 }
 
 static inline int inet_sk_bound_l3mdev(const struct sock *sk)
-- 
2.36.0.512.ge40c2bad7a-goog