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Subject[PATCH 5.4 262/434] net: avoid potential false sharing in neighbor related code
Date
From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 25c7a6d1f90e208ec27ca854b1381ed39842ec57 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 718e62fbe869..013396e50b91 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1940,8 +1940,8 @@ 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)
@@ -1951,10 +1951,10 @@ 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);
}
}

--
2.20.1


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