From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755700AbcKOPne (ORCPT ); Tue, 15 Nov 2016 10:43:34 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:34404 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753270AbcKOPnc (ORCPT ); Tue, 15 Nov 2016 10:43:32 -0500 Date: Tue, 15 Nov 2016 07:43:23 -0800 From: "Paul E. McKenney" To: Peter Zijlstra Cc: Mathieu Desnoyers , linux-kernel , Ingo Molnar , Lai Jiangshan , dipankar , Andrew Morton , Josh Triplett , Thomas Gleixner , rostedt , David Howells , Eric Dumazet , dvhart , fweisbec , Oleg Nesterov , bobby prani , ldr709 Subject: Re: [PATCH RFC tip/core/rcu] SRCU rewrite Reply-To: paulmck@linux.vnet.ibm.com References: <20161114183636.GA28589@linux.vnet.ibm.com> <20161115075113.GN3142@twins.programming.kicks-ass.net> <1857730044.1901.1479218090893.JavaMail.zimbra@efficios.com> <20161115135912.GJ3142@twins.programming.kicks-ass.net> <20161115142627.GX4127@linux.vnet.ibm.com> <20161115145536.GE11311@worktop.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161115145536.GE11311@worktop.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16111515-0028-0000-0000-0000060A64A8 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00006082; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000189; SDB=6.00781043; UDB=6.00376709; IPR=6.00558551; BA=6.00004883; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00013334; XFM=3.00000011; UTC=2016-11-15 15:43:29 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16111515-0029-0000-0000-000030DD5349 Message-Id: <20161115154323.GB4127@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-11-15_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-1611150276 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 15, 2016 at 03:55:36PM +0100, Peter Zijlstra wrote: > On Tue, Nov 15, 2016 at 06:26:27AM -0800, Paul E. McKenney wrote: > > On Tue, Nov 15, 2016 at 02:59:12PM +0100, Peter Zijlstra wrote: > > > > The smp_mb()s in read_{un,}lock() and the lock in call_srcu() come to > > > mind. > > > > There is some possibility of weakening the srcu_read_unlock() ordering, > > but one step at a time. > > > > Has the lock in call_srcu() been causing trouble? Easy to fix if so, > > but as you noted in another email today, we don't need complexity for > > complexity's sake. And no reports of problems with this have reached > > me thus far. > > It was a cause for concern in the optimistic fault series, but since > that never got sorted, it hasn't shown up in practise afaik. Sounds like it is not too early for me to be thinking about fixes, probably similar to the approach used for expedited grace periods. And thank you for letting me know! Thanx, Paul