From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759554AbcKCRtU (ORCPT ); Thu, 3 Nov 2016 13:49:20 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:41675 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1758064AbcKCRtS (ORCPT ); Thu, 3 Nov 2016 13:49:18 -0400 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> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16110317-0020-0000-0000-00000A2AD399 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00006027; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000189; SDB=6.00776313; UDB=6.00373416; IPR=6.00553472; BA=6.00004855; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00013202; XFM=3.00000011; UTC=2016-11-03 17:49:15 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16110317-0021-0000-0000-000056F949E5 Message-Id: <20161103174911.GL3716@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-11-03_05:,, 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-1611030330 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 >