From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932493AbcKHGfx (ORCPT ); Tue, 8 Nov 2016 01:35:53 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:34749 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932294AbcKHGfI (ORCPT ); Tue, 8 Nov 2016 01:35:08 -0500 Date: Mon, 7 Nov 2016 12:03:15 -0800 From: "Paul E. McKenney" To: Mathieu Desnoyers Cc: linux-kernel , Josh Triplett , rostedt , Lai Jiangshan , stable 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> <20161103174911.GL3716@linux.vnet.ibm.com> <656710430.17218.1478538539895.JavaMail.zimbra@efficios.com> <20161107180614.GR24166@linux.vnet.ibm.com> <1462452244.17824.1478542214440.JavaMail.zimbra@efficios.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1462452244.17824.1478542214440.JavaMail.zimbra@efficios.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16110806-0028-0000-0000-000005F8AA3C X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00006040; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000189; SDB=6.00778042; UDB=6.00374663; IPR=6.00555360; BA=6.00004862; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00013247; XFM=3.00000011; UTC=2016-11-08 06:35:04 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16110806-0029-0000-0000-000030A6F7A5 Message-Id: <20161107200315.GA3438@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-11-08_02:,, 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-1611080120 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 07, 2016 at 06:10:14PM +0000, Mathieu Desnoyers wrote: > > ----- On Nov 7, 2016, at 1:06 PM, Paul E. McKenney paulmck@linux.vnet.ibm.com wrote: > > > On Mon, Nov 07, 2016 at 05:08:59PM +0000, Mathieu Desnoyers wrote: > >> ----- On Nov 3, 2016, at 1:49 PM, Paul E. McKenney paulmck@linux.vnet.ibm.com > >> wrote: > >> > >> > 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" > >> > >> Hi Paul, > >> > >> Do you plan to pick it up through your tree, or I should sent > >> it directly to Linus ? > > > > Your choice. I believe that the original went some other way, but I > > would be fine carrying this one. > > Not sure what you mean by "the original" ? And which other way ? > I have not been notified about this. If I remember correctly, you sent the original sys_membarrier() patch through akpm or similar. > If you can carry this patch it would be very much appreciated, Will do! Thanx, Paul > Thanks, > > Mathieu > > > > > Thanx, Paul > > > >> Thanks, > >> > >> Mathieu > >> > >> > > >> >> 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 > >> > >> -- > >> Mathieu Desnoyers > >> EfficiOS Inc. > >> http://www.efficios.com > > -- > Mathieu Desnoyers > EfficiOS Inc. > http://www.efficios.com >