From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758921AbcKCQ3x (ORCPT ); Thu, 3 Nov 2016 12:29:53 -0400 Received: from mail.efficios.com ([167.114.142.141]:43984 "EHLO mail.efficios.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758722AbcKCQ3v (ORCPT ); Thu, 3 Nov 2016 12:29:51 -0400 From: Mathieu Desnoyers To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, Mathieu Desnoyers , Josh Triplett , Steven Rostedt , Lai Jiangshan , Subject: [PATCH] Fix: disable sys_membarrier when nohz_full is enabled Date: Thu, 3 Nov 2016 10:29:28 -0600 Message-Id: <1478190568-5829-1-git-send-email-mathieu.desnoyers@efficios.com> X-Mailer: git-send-email 2.1.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Userspace applications should be allowed to expect the membarrier system call with MEMBARRIER_CMD_SHARED command to issue memory barriers on nohz_full CPUs, but synchronize_sched() does not take those into account. Given that we do not want unrelated processes to be able to affect real-time sensitive nohz_full CPUs, simply return ENOSYS when membarrier is invoked on a kernel with enabled nohz_full CPUs. Signed-off-by: Mathieu Desnoyers CC: "Paul E. McKenney" CC: Josh Triplett CC: Steven Rostedt CC: Lai Jiangshan CC: [3.10+] --- kernel/membarrier.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/kernel/membarrier.c b/kernel/membarrier.c index 536c727..9f9284f 100644 --- a/kernel/membarrier.c +++ b/kernel/membarrier.c @@ -16,6 +16,7 @@ #include #include +#include /* * Bitmask made from a "or" of all commands within enum membarrier_cmd, @@ -51,6 +52,9 @@ */ SYSCALL_DEFINE2(membarrier, int, cmd, int, flags) { + /* MEMBARRIER_CMD_SHARED is not compatible with nohz_full. */ + if (tick_nohz_full_enabled()) + return -ENOSYS; if (unlikely(flags)) return -EINVAL; switch (cmd) { -- 2.1.4