Subject: [PATCH AUTOSEL 4.19 591/671] tcp: annotate lockless access to tcp_memory_pressure

From: Sasha Levin <[email-masked]>
Date: Thu, 16 Jan 2020 12:03:49 -0500

From: Eric Dumazet <[email-masked]>

[ 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 <[email-masked]>
Signed-off-by: Jakub Kicinski <[email-masked]>
Signed-off-by: Sasha Levin <[email-masked]>
---
 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 ac4ffe8013d8..918bfd0d7d1f 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 7561fa1bcc3e..3c181ca714d0 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