From 25c7a6d1f90e208ec27ca854b1381ed39842ec57 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Tue, 5 Nov 2019 14:11:51 -0800 Subject: [PATCH] net: avoid potential false sharing in neighbor related code 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 Signed-off-by: David S. Miller --- include/net/arp.h | 4 ++-- include/net/ndisc.h | 8 ++++---- include/net/sock.h | 12 ++++++------ 3 files changed, 12 insertions(+), 12 deletions(-) diff --git a/include/net/arp.h b/include/net/arp.h index c8f580a0e6b1..4950191f6b2b 100644 --- a/include/net/arp.h +++ b/include/net/arp.h @@ -57,8 +57,8 @@ static inline void __ipv4_confirm_neigh(struct net_device *dev, u32 key) 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(); } diff --git a/include/net/ndisc.h b/include/net/ndisc.h index b2f715ca0567..b5ebeb3b0de0 100644 --- a/include/net/ndisc.h +++ b/include/net/ndisc.h @@ -414,8 +414,8 @@ static inline void __ipv6_confirm_neigh(struct net_device *dev, 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(); } @@ -431,8 +431,8 @@ static inline void __ipv6_confirm_neigh_stub(struct net_device *dev, 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(); } diff --git a/include/net/sock.h b/include/net/sock.h index ac6042d0af32..f2f853439b65 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -1939,8 +1939,8 @@ struct dst_entry *sk_dst_check(struct sock *sk, u32 cookie); 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) @@ -1950,10 +1950,10 @@ static inline void sock_confirm_neigh(struct sk_buff *skb, struct neighbour *n) 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); } } -- 2.11.0