From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933183AbdCJJOg (ORCPT ); Fri, 10 Mar 2017 04:14:36 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:35954 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932962AbdCJJOU (ORCPT ); Fri, 10 Mar 2017 04:14:20 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Mathieu Desnoyers , Josh Triplett , Steven Rostedt , "Paul E. McKenney" , Frederic Weisbecker , Chris Metcalf , Rik van Riel , Lai Jiangshan Subject: [PATCH 4.4 40/91] Fix: Disable sys_membarrier when nohz_full is enabled Date: Fri, 10 Mar 2017 10:08:39 +0100 Message-Id: <20170310083902.790421433@linuxfoundation.org> X-Mailer: git-send-email 2.12.0 In-Reply-To: <20170310083900.730556986@linuxfoundation.org> References: <20170310083900.730556986@linuxfoundation.org> User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Mathieu Desnoyers commit 907565337ebf998a68cb5c5b2174ce5e5da065eb upstream. 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: Josh Triplett CC: Steven Rostedt Signed-off-by: Paul E. McKenney Cc: Frederic Weisbecker Cc: Chris Metcalf Cc: Rik van Riel Acked-by: Lai Jiangshan Reviewed-by: Josh Triplett Signed-off-by: Greg Kroah-Hartman --- kernel/membarrier.c | 4 ++++ 1 file changed, 4 insertions(+) --- 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) {