From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:57528 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932766AbcKGSwM (ORCPT ); Mon, 7 Nov 2016 13:52:12 -0500 Received: from pps.filterd (m0098404.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.17/8.16.0.17) with SMTP id uA7I4JhK088255 for ; Mon, 7 Nov 2016 13:06:21 -0500 Received: from e37.co.us.ibm.com (e37.co.us.ibm.com [32.97.110.158]) by mx0a-001b2d01.pphosted.com with ESMTP id 26jvt7sn4j-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Mon, 07 Nov 2016 13:06:21 -0500 Received: from localhost by e37.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 7 Nov 2016 11:06:20 -0700 Date: Mon, 7 Nov 2016 10:06:14 -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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <656710430.17218.1478538539895.JavaMail.zimbra@efficios.com> Message-Id: <20161107180614.GR24166@linux.vnet.ibm.com> Sender: stable-owner@vger.kernel.org List-ID: 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. 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 >