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Subject[PATCH 4.19 601/639] tcp: annotate lockless access to tcp_memory_pressure
Date
From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 1f142c17d19a5618d5a633195a46f2c8be9bf232 ]

tcp_memory_pressure is read without holding any lock,
and its value could be changed on other cpus.

Use READ_ONCE() to annotate these lockless reads.

The write side is already using atomic ops.

Fixes: b8da51ebb1aa ("tcp: introduce tcp_under_memory_pressure()")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/net/tcp.h | 2 +-
net/ipv4/tcp.c | 4 ++--
2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index ac4ffe8013d8a..918bfd0d7d1f9 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -261,7 +261,7 @@ static inline bool tcp_under_memory_pressure(const struct sock *sk)
mem_cgroup_under_socket_pressure(sk->sk_memcg))
return true;

- return tcp_memory_pressure;
+ return READ_ONCE(tcp_memory_pressure);
}
/*
* The next routines deal with comparing 32 bit unsigned ints
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index cd8a92e7a39eb..af9361eba64a6 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -325,7 +325,7 @@ void tcp_enter_memory_pressure(struct sock *sk)
{
unsigned long val;

- if (tcp_memory_pressure)
+ if (READ_ONCE(tcp_memory_pressure))
return;
val = jiffies;

@@ -340,7 +340,7 @@ void tcp_leave_memory_pressure(struct sock *sk)
{
unsigned long val;

- if (!tcp_memory_pressure)
+ if (!READ_ONCE(tcp_memory_pressure))
return;
val = xchg(&tcp_memory_pressure, 0);
if (val)
--
2.20.1


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