From: Eric Dumazet <edumazet@google.com>
Date: Tue, 5 Nov 2019 14:11:51 -0800
Subject: net: avoid potential false sharing in neighbor related code
Patch-mainline: v5.5-rc1
Git-commit: 25c7a6d1f90e208ec27ca854b1381ed39842ec57
References: bsc#1154353

There are common instances of the following construct :

	if (n->confirmed != now)
		n->confirmed = now;

A C compiler could legally remove the conditional.

Use READ_ONCE()/WRITE_ONCE() to avoid this problem.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 include/net/arp.h   |    4 ++--
 include/net/ndisc.h |    8 ++++----
 include/net/sock.h  |   12 ++++++------
 3 files changed, 12 insertions(+), 12 deletions(-)

--- a/include/net/arp.h
+++ b/include/net/arp.h
@@ -57,8 +57,8 @@ static inline void __ipv4_confirm_neigh(
 		unsigned long now = jiffies;
 
 		/* avoid dirtying neighbour */
-		if (n->confirmed != now)
-			n->confirmed = now;
+		if (READ_ONCE(n->confirmed) != now)
+			WRITE_ONCE(n->confirmed, now);
 	}
 	rcu_read_unlock_bh();
 }
--- a/include/net/ndisc.h
+++ b/include/net/ndisc.h
@@ -413,8 +413,8 @@ static inline void __ipv6_confirm_neigh(
 		unsigned long now = jiffies;
 
 		/* avoid dirtying neighbour */
-		if (n->confirmed != now)
-			n->confirmed = now;
+		if (READ_ONCE(n->confirmed) != now)
+			WRITE_ONCE(n->confirmed, now);
 	}
 	rcu_read_unlock_bh();
 }
@@ -430,8 +430,8 @@ static inline void __ipv6_confirm_neigh_
 		unsigned long now = jiffies;
 
 		/* avoid dirtying neighbour */
-		if (n->confirmed != now)
-			n->confirmed = now;
+		if (READ_ONCE(n->confirmed) != now)
+			WRITE_ONCE(n->confirmed, now);
 	}
 	rcu_read_unlock_bh();
 }
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1940,8 +1940,8 @@ struct dst_entry *sk_dst_check(struct so
 
 static inline void sk_dst_confirm(struct sock *sk)
 {
-	if (!sk->sk_dst_pending_confirm)
-		sk->sk_dst_pending_confirm = 1;
+	if (!READ_ONCE(sk->sk_dst_pending_confirm))
+		WRITE_ONCE(sk->sk_dst_pending_confirm, 1);
 }
 
 static inline void sock_confirm_neigh(struct sk_buff *skb, struct neighbour *n)
@@ -1951,10 +1951,10 @@ static inline void sock_confirm_neigh(st
 		unsigned long now = jiffies;
 
 		/* avoid dirtying neighbour */
-		if (n->confirmed != now)
-			n->confirmed = now;
-		if (sk && sk->sk_dst_pending_confirm)
-			sk->sk_dst_pending_confirm = 0;
+		if (READ_ONCE(n->confirmed) != now)
+			WRITE_ONCE(n->confirmed, now);
+		if (sk && READ_ONCE(sk->sk_dst_pending_confirm))
+			WRITE_ONCE(sk->sk_dst_pending_confirm, 0);
 	}
 }