From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752741AbdERDtO (ORCPT ); Wed, 17 May 2017 23:49:14 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:58047 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750838AbdERDtM (ORCPT ); Wed, 17 May 2017 23:49:12 -0400 Date: Wed, 17 May 2017 20:48:59 -0700 From: "Paul E. McKenney" To: Steven Rostedt Cc: LKML , Ingo Molnar , Thomas Gleixner Subject: Re: [PATCH] tracing: Make sure RCU is watching before calling a stack trace Reply-To: paulmck@linux.vnet.ibm.com References: <20170517220845.17f93eca@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170517220845.17f93eca@gandalf.local.home> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 17051803-0040-0000-0000-0000034139F6 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00007080; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000212; SDB=6.00862040; UDB=6.00427620; IPR=6.00641699; BA=6.00005356; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00015498; XFM=3.00000015; UTC=2017-05-18 03:49:02 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17051803-0041-0000-0000-00000735690B Message-Id: <20170518034859.GQ3956@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-05-18_01:,, 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=8.0.1-1703280000 definitions=main-1705180026 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 17, 2017 at 10:08:45PM -0400, Steven Rostedt wrote: > > From: "Steven Rostedt (VMware)" > > As stack tracing now requires "rcu watching", force RCU to be watching when > recording a stack trace. > > Link: http://lkml.kernel.org/r/20170512172449.879684501@goodmis.org > > Cc: "Paul E. McKenney" > Signed-off-by: Steven Rostedt (VMware) Looks correct to me. Acked-by: Paul E. McKenney > --- > kernel/trace/trace.c | 23 ++++++++++++++++++++++- > 1 file changed, 22 insertions(+), 1 deletion(-) > > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > index fcc9a2d..a1b45b4 100644 > --- a/kernel/trace/trace.c > +++ b/kernel/trace/trace.c > @@ -2568,7 +2568,28 @@ static inline void ftrace_trace_stack(struct trace_array *tr, > void __trace_stack(struct trace_array *tr, unsigned long flags, int skip, > int pc) > { > - __ftrace_trace_stack(tr->trace_buffer.buffer, flags, skip, pc, NULL); > + struct ring_buffer *buffer = tr->trace_buffer.buffer; > + > + /* When an NMI triggers, RCU is enabled via rcu_nmi_enter() */ > + if (in_nmi()) { > + __ftrace_trace_stack(buffer, flags, skip, pc, NULL); > + return; > + } > + > + /* > + * It is possible that a function is being traced in a > + * location that RCU is not watching. A call to > + * rcu_irq_enter() will make sure that it is, but there's > + * a few internal rcu functions that could be traced > + * where that wont work either. In those cases, we just > + * do nothing. > + */ > + if (unlikely(rcu_irq_enter_disabled())) > + return; > + > + rcu_irq_enter(); > + __ftrace_trace_stack(buffer, flags, skip, pc, NULL); > + rcu_irq_exit(); > } > > /** > -- > 2.9.3 >