From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:47503 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932329AbcKQSEM (ORCPT ); Thu, 17 Nov 2016 13:04:12 -0500 Received: from pps.filterd (m0098396.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.17/8.16.0.17) with SMTP id uAHDcjxm085359 for ; Thu, 17 Nov 2016 08:39:03 -0500 Received: from e33.co.us.ibm.com (e33.co.us.ibm.com [32.97.110.151]) by mx0a-001b2d01.pphosted.com with ESMTP id 26s8fqr66w-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Thu, 17 Nov 2016 08:39:03 -0500 Received: from localhost by e33.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 17 Nov 2016 06:39:01 -0700 Date: Thu, 17 Nov 2016 05:38:59 -0800 From: "Paul E. McKenney" To: Lai Jiangshan Cc: Mathieu Desnoyers , LKML , Josh Triplett , Steven Rostedt , 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: Message-Id: <20161117133859.GS3612@linux.vnet.ibm.com> Sender: stable-owner@vger.kernel.org List-ID: On Thu, Nov 17, 2016 at 02:51:26PM +0800, Lai Jiangshan wrote: > On Fri, Nov 4, 2016 at 12:29 AM, 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" > > 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; > > I guess this code needs to be moved down into the branch of > "case MEMBARRIER_CMD_SHARED" to match its comment. > > Acked-by: Lai Jiangshan Added, thank you! > But I'm afraid, in the future, tick_nohz_full will become a default y > feature. thus it makes sys_membarrier() always disabled. we might > need a new MEMBARRIER_CMD_XXX to handle it? Makes a lot of sense to me! Thanx, Paul