From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753371AbdDJS3J (ORCPT ); Mon, 10 Apr 2017 14:29:09 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:35090 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752410AbdDJS3H (ORCPT ); Mon, 10 Apr 2017 14:29:07 -0400 Date: Mon, 10 Apr 2017 11:29:01 -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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170410181151.708413295@goodmis.org> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 17041018-0036-0000-0000-000001D84084 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00006912; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000208; SDB=6.00845663; UDB=6.00417041; IPR=6.00624097; 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=3.00014995; XFM=3.00000013; UTC=2017-04-10 18:29:03 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17041018-0037-0000-0000-00003F9895BC Message-Id: <20170410182901.GX1600@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-1704100146 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Again, I am not necessarily agitating for this change now, just getting this possibility on the record. ;-) Thanx, Paul > --- > include/linux/tracepoint.h | 19 +++++++++++-------- > 1 file changed, 11 insertions(+), 8 deletions(-) > > diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h > index f72fcfe0e66a..cc48cb2ce209 100644 > --- a/include/linux/tracepoint.h > +++ b/include/linux/tracepoint.h > @@ -128,7 +128,7 @@ extern void syscall_unregfunc(void); > * as "(void *, void)". The DECLARE_TRACE_NOARGS() will pass in just > * "void *data", where as the DECLARE_TRACE() will pass in "void *data, proto". > */ > -#define __DO_TRACE(tp, proto, args, cond, prercu, postrcu) \ > +#define __DO_TRACE(tp, proto, args, cond, rcucheck) \ > do { \ > struct tracepoint_func *it_func_ptr; \ > void *it_func; \ > @@ -136,7 +136,11 @@ extern void syscall_unregfunc(void); > \ > if (!(cond)) \ > return; \ > - prercu; \ > + if (rcucheck) { \ > + if (WARN_ON_ONCE(rcu_irq_enter_disabled())) \ > + return; \ > + rcu_irq_enter_irqson(); \ > + } \ > rcu_read_lock_sched_notrace(); \ > it_func_ptr = rcu_dereference_sched((tp)->funcs); \ > if (it_func_ptr) { \ > @@ -147,20 +151,19 @@ extern void syscall_unregfunc(void); > } while ((++it_func_ptr)->func); \ > } \ > rcu_read_unlock_sched_notrace(); \ > - postrcu; \ > + if (rcucheck) \ > + rcu_irq_exit_irqson(); \ > } while (0) > > #ifndef MODULE > -#define __DECLARE_TRACE_RCU(name, proto, args, cond, data_proto, data_args) \ > +#define __DECLARE_TRACE_RCU(name, proto, args, cond, data_proto, data_args) \ > static inline void trace_##name##_rcuidle(proto) \ > { \ > if (static_key_false(&__tracepoint_##name.key)) \ > __DO_TRACE(&__tracepoint_##name, \ > TP_PROTO(data_proto), \ > TP_ARGS(data_args), \ > - TP_CONDITION(cond), \ > - rcu_irq_enter_irqson(), \ > - rcu_irq_exit_irqson()); \ > + TP_CONDITION(cond), 1); \ > } > #else > #define __DECLARE_TRACE_RCU(name, proto, args, cond, data_proto, data_args) > @@ -186,7 +189,7 @@ extern void syscall_unregfunc(void); > __DO_TRACE(&__tracepoint_##name, \ > TP_PROTO(data_proto), \ > TP_ARGS(data_args), \ > - TP_CONDITION(cond),,); \ > + TP_CONDITION(cond), 0); \ > if (IS_ENABLED(CONFIG_LOCKDEP) && (cond)) { \ > rcu_read_lock_sched_notrace(); \ > rcu_dereference_sched(__tracepoint_##name.funcs);\ > -- > 2.10.2 > >