Commit 503978ac authored Oct 09, 2019 by Eric Dumazet Committed by Jakub Kicinski Oct 09, 2019

net: avoid possible false sharing in sk_leave_memory_pressure()

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: 06044751 ("tcp: add TCPMemoryPressuresChrono counter")
Fixes: 180d8cd9 ("foundations of per-cgroup memory pressure controlling.")
Fixes: 3ab224be ("[NET] CORE: Introducing new memory accounting interface.")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>

parent 4ffdd22e

net/core/sock.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -2334,8 +2334,8 @@ static void sk_leave_memory_pressure(struct sock *sk)
		} 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);
		}
		}