From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932420AbdJJPcq (ORCPT ); Tue, 10 Oct 2017 11:32:46 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:55084 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S932278AbdJJPcm (ORCPT ); Tue, 10 Oct 2017 11:32:42 -0400 Date: Tue, 10 Oct 2017 08:32:35 -0700 From: "Paul E. McKenney" To: Mathieu Desnoyers Cc: rostedt , linux-kernel , Ingo Molnar , Linus Torvalds , Mark Rutland , David Howells , linux-arch , Peter Zijlstra , Will Deacon Subject: Re: [PATCH RFC tip/core/rcu 11/15] tracepoint: Remove smp_read_barrier_depends() from comment Reply-To: paulmck@linux.vnet.ibm.com References: <20171010001951.GA6476@linux.vnet.ibm.com> <1507594969-8347-11-git-send-email-paulmck@linux.vnet.ibm.com> <20171009203116.4246818c@gandalf.local.home> <506678791.34748.1507597958832.JavaMail.zimbra@efficios.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <506678791.34748.1507597958832.JavaMail.zimbra@efficios.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 17101015-0048-0000-0000-000001F37A1B X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00007873; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000235; SDB=6.00929160; UDB=6.00467649; IPR=6.00709431; BA=6.00005632; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00017475; XFM=3.00000015; UTC=2017-10-10 15:32:38 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17101015-0049-0000-0000-000042D3534C Message-Id: <20171010153235.GC3521@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-10-10_04:,, 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=8.0.1-1707230000 definitions=main-1710100218 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 10, 2017 at 01:12:38AM +0000, Mathieu Desnoyers wrote: > ----- On Oct 9, 2017, at 8:31 PM, rostedt rostedt@goodmis.org wrote: > > > [ added Mathieu ] > > > > On Mon, 9 Oct 2017 17:22:45 -0700 > > "Paul E. McKenney" wrote: > > > >> The comment in tracepoint_add_func() mentions smp_read_barrier_depends(), > >> whose use should be quite restricted. This commit updates the comment > >> to instead mention the smp_store_release() and rcu_dereference_sched() > >> that the current code actually uses. > >> > >> Signed-off-by: Paul E. McKenney > >> Cc: Ingo Molnar > >> Cc: Steven Rostedt > > > > Acked-by: Steven Rostedt (VMware) > > > > Yeah I think we don't need to spell out the implementation of > rcu_dereference_sched() there (which actually uses lockless_dereference(), > which indeed ends up relying on smp_read_barrier_depends()). The comment > was a bit too low-level for the benefit of its audience. > > I agree with the change. > > Acked-by: Mathieu Desnoyers Applied, thank you both! Thanx, Paul > Thanks, > > Mathieu > > > -- Steve > > > >> --- > >> kernel/tracepoint.c | 9 ++++----- > >> 1 file changed, 4 insertions(+), 5 deletions(-) > >> > >> diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c > >> index 685c50ae6300..671b13457387 100644 > >> --- a/kernel/tracepoint.c > >> +++ b/kernel/tracepoint.c > >> @@ -212,11 +212,10 @@ static int tracepoint_add_func(struct tracepoint *tp, > >> } > >> > >> /* > >> - * rcu_assign_pointer has a smp_wmb() which makes sure that the new > >> - * probe callbacks array is consistent before setting a pointer to it. > >> - * This array is referenced by __DO_TRACE from > >> - * include/linux/tracepoints.h. A matching smp_read_barrier_depends() > >> - * is used. > >> + * rcu_assign_pointer has as smp_store_release() which makes sure > >> + * that the new probe callbacks array is consistent before setting > >> + * a pointer to it. This array is referenced by __DO_TRACE from > >> + * include/linux/tracepoint.h using rcu_dereference_sched(). > >> */ > >> rcu_assign_pointer(tp->funcs, tp_funcs); > > > if (!static_key_enabled(&tp->key)) > > -- > Mathieu Desnoyers > EfficiOS Inc. > http://www.efficios.com >