From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:57729 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1758493AbcKCRtS (ORCPT ); Thu, 3 Nov 2016 13:49:18 -0400 Received: from pps.filterd (m0098419.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.17/8.16.0.17) with SMTP id uA3Hn68w099045 for ; Thu, 3 Nov 2016 13:49:17 -0400 Received: from e36.co.us.ibm.com (e36.co.us.ibm.com [32.97.110.154]) by mx0b-001b2d01.pphosted.com with ESMTP id 26g765t1wt-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Thu, 03 Nov 2016 13:49:17 -0400 Received: from localhost by e36.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 3 Nov 2016 11:49:16 -0600 Date: Thu, 3 Nov 2016 10:49:11 -0700 From: "Paul E. McKenney" To: Mathieu Desnoyers Cc: linux-kernel@vger.kernel.org, Josh Triplett , Steven Rostedt , Lai Jiangshan , stable@vger.kernel.org Subject: Re: [PATCH] Fix: disable sys_membarrier when nohz_full is enabled Reply-To: paulmck@linux.vnet.ibm.com References: <1478190568-5829-1-git-send-email-mathieu.desnoyers@efficios.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1478190568-5829-1-git-send-email-mathieu.desnoyers@efficios.com> Message-Id: <20161103174911.GL3716@linux.vnet.ibm.com> Sender: stable-owner@vger.kernel.org List-ID: On Thu, Nov 03, 2016 at 10:29:28AM -0600, Mathieu Desnoyers wrote: > 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" Acked-by: "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 >