From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S941070AbcKQR1a (ORCPT ); Thu, 17 Nov 2016 12:27:30 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:42457 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932596AbcKQR10 (ORCPT ); Thu, 17 Nov 2016 12:27:26 -0500 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: User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16111713-0008-0000-0000-000006194CDA X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00006094; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000189; SDB=6.00781942; UDB=6.00377260; IPR=6.00559446; BA=6.00004889; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00013361; XFM=3.00000011; UTC=2016-11-17 13:39:00 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16111713-0009-0000-0000-00003D169025 Message-Id: <20161117133859.GS3612@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-11-17_06:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1609300000 definitions=main-1611170247 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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