From: Eric Dumazet <edumazet@google.com>
Date: Wed, 9 Oct 2019 12:55:53 -0700
Subject: net: avoid possible false sharing in sk_leave_memory_pressure()
Patch-mainline: v5.4-rc4
Git-commit: 503978aca46124cd714703e180b9c8292ba50ba7
References: bsc#1154353
As mentioned in https://github.com/google/ktsan/wiki/READ_ONCE-and-WRITE_ONCE#it-may-improve-performance
a C compiler can legally transform :
if (memory_pressure && *memory_pressure)
*memory_pressure = 0;
to :
if (memory_pressure)
*memory_pressure = 0;
Fixes: 0604475119de ("tcp: add TCPMemoryPressuresChrono counter")
Fixes: 180d8cd942ce ("foundations of per-cgroup memory pressure controlling.")
Fixes: 3ab224be6d69 ("[NET] CORE: Introducing new memory accounting interface.")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
net/core/sock.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -2334,8 +2334,8 @@ static void sk_leave_memory_pressure(str
} else {
unsigned long *memory_pressure = sk->sk_prot->memory_pressure;
- if (memory_pressure && *memory_pressure)
- *memory_pressure = 0;
+ if (memory_pressure && READ_ONCE(*memory_pressure))
+ WRITE_ONCE(*memory_pressure, 0);
}
}