Commit 25c7a6d1 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

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: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 3828a93f

include/net/arp.h

+2 −2
Original line number Diff line number Diff line
@@ -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();

}

include/net/ndisc.h

+4 −4
Original line number Diff line number Diff line
@@ -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();

}

include/net/sock.h

+6 −6
Original line number Diff line number Diff line
@@ -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);

	}

}