From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752515AbdDJSga (ORCPT ); Mon, 10 Apr 2017 14:36:30 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:56199 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751527AbdDJSg3 (ORCPT ); Mon, 10 Apr 2017 14:36:29 -0400 Date: Mon, 10 Apr 2017 11:36:24 -0700 From: "Paul E. McKenney" To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Andrew Morton , Mathieu Desnoyers Subject: Re: [PATCH 7/7 v3] tracing: Make sure rcu_irq_enter() can work for trace_*_rcuidle() trace events Reply-To: paulmck@linux.vnet.ibm.com References: <20170410181005.420764935@goodmis.org> <20170410181151.708413295@goodmis.org> <20170410182901.GX1600@linux.vnet.ibm.com> <20170410143240.6828c13c@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170410143240.6828c13c@gandalf.local.home> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 17041018-0008-0000-0000-000001EE472B X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00006912; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000208; SDB=6.00845666; UDB=6.00417043; IPR=6.00624099; BA=6.00005281; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00014996; XFM=3.00000013; UTC=2017-04-10 18:36:26 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17041018-0009-0000-0000-0000348799D2 Message-Id: <20170410183624.GA1600@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-04-10_14:,, 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=8.0.1-1702020001 definitions=main-1704100147 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 10, 2017 at 02:32:40PM -0400, Steven Rostedt wrote: > On Mon, 10 Apr 2017 11:29:01 -0700 > "Paul E. McKenney" wrote: > > > On Mon, Apr 10, 2017 at 02:10:12PM -0400, Steven Rostedt wrote: > > > From: "Steven Rostedt (VMware)" > > > > > > Stack tracing discovered that there's a small location inside the RCU > > > infrastructure where calling rcu_irq_enter() does not work. As trace events > > > use rcu_irq_enter() it must make sure that it is functionable. A check > > > against rcu_irq_enter_disabled() is added with a WARN_ON_ONCE() as no trace > > > event should ever be used in that part of RCU. If the warning is triggered, > > > then the trace event is ignored. > > > > > > Restructure the __DO_TRACE() a bit to get rid of the prercu and postrcu, > > > and just have an rcucheck that does the work from within the _DO_TRACE() > > > macro. gcc optimization will compile out the rcucheck=0 case. > > > > > > Link: http://lkml.kernel.org/r/20170405093207.404f8deb@gandalf.local.home > > > > > > Acked-by: Mathieu Desnoyers > > > Signed-off-by: Steven Rostedt (VMware) > > > > Acked-by: Paul E. McKenney > > > > As an aside, it looks like the rcu_irq_enter_disabled() settings > > in the RCU idle-entry code could be placed under CONFIG_PROVE_RCU=y > > should my idle-entry-overhead concerns prove to be well-founded. > > The errors would be caught during testing, but no production-side > > overhead. > > Even with the underscored __this_cpu_*() calls? That change did not completely address my concerns, but it did make me willing to take a wait-and-see attitude. ;-) > > Again, I am not necessarily agitating for this change now, just getting > > this possibility on the record. ;-) > > That would be easy to add :-) But we can do that at a later time. Agreed, if it is actually needed. The usual suspects will no doubt be quick to let us know if it is needed. Thanx, Pau