From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758676AbdELSZm (ORCPT ); Fri, 12 May 2017 14:25:42 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:53870 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757884AbdELSZl (ORCPT ); Fri, 12 May 2017 14:25:41 -0400 Date: Fri, 12 May 2017 11:25:35 -0700 From: "Paul E. McKenney" To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, Thomas Gleixner , Peter Zijlstra , Ingo Molnar , Mathieu Desnoyers , Masami Hiramatsu Subject: Re: [RFC][PATCH 1/5] tracing: Make sure RCU is watching before calling a stack trace Reply-To: paulmck@linux.vnet.ibm.com References: <20170512171544.100715273@goodmis.org> <20170512172449.879684501@goodmis.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170512172449.879684501@goodmis.org> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 17051218-0040-0000-0000-0000033B3FA1 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00007051; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000211; SDB=6.00859618; UDB=6.00426124; IPR=6.00639201; BA=6.00005345; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00015430; XFM=3.00000015; UTC=2017-05-12 18:25:38 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17051218-0041-0000-0000-0000072F69B8 Message-Id: <20170512182535.GZ3956@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-05-12_10:,, 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-1705120343 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, May 12, 2017 at 01:15:45PM -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. > > Signed-off-by: Steven Rostedt (VMware) Assuming that you never get to __trace_stack() if in an NMI handler, this looks good to me! In contrast, if if __trace_stack() ever is called from an NMI handler, invoking rcu_irq_enter() can be fatal. Thanx, Paul > --- > kernel/trace/trace.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > index c4536c449021..a4208cebb42b 100644 > --- a/kernel/trace/trace.c > +++ b/kernel/trace/trace.c > @@ -2568,7 +2568,12 @@ static inline void ftrace_trace_stack(struct trace_array *tr, > void __trace_stack(struct trace_array *tr, unsigned long flags, int skip, > int pc) > { > + if (unlikely(rcu_irq_enter_disabled())) > + return; > + > + rcu_irq_enter(); > __ftrace_trace_stack(tr->trace_buffer.buffer, flags, skip, pc, NULL); > + rcu_irq_exit(); > } > > /** > -- > 2.10.2 > >