From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933378AbdESBof (ORCPT ); Thu, 18 May 2017 21:44:35 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:39721 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S932574AbdESBo3 (ORCPT ); Thu, 18 May 2017 21:44:29 -0400 Date: Thu, 18 May 2017 18:44:23 -0700 From: "Paul E. McKenney" To: Steven Rostedt Cc: LKML , Ingo Molnar , Thomas Gleixner Subject: Re: [PATCH v3] tracing: Make sure RCU is watching before calling a stack trace Reply-To: paulmck@linux.vnet.ibm.com References: <20170518211140.09eeac00@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170518211140.09eeac00@gandalf.local.home> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 17051901-0056-0000-0000-000003699307 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00007083; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000212; SDB=6.00862378; UDB=6.00427872; IPR=6.00642120; BA=6.00005358; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00015505; XFM=3.00000015; UTC=2017-05-19 01:44:26 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17051901-0057-0000-0000-0000079FC1D6 Message-Id: <20170519014423.GA3956@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-05-18_06:,, 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-1705190010 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 18, 2017 at 09:11:40PM -0400, Steven Rostedt wrote: > From 8260b0308d3ee0f836cd5ea4b177efeb52ab151f Mon Sep 17 00:00:00 2001 > From: "Steven Rostedt (VMware)" > Date: Fri, 12 May 2017 13:15:45 -0400 > Subject: [PATCH] tracing: Make sure RCU is watching before calling a stack > trace > > 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) Acked-by: Paul E. McKenney > --- > > Changes since v2: > > Use rcu_is_watching() instead if checking for in_nmi() and irqs > disabled. But now if rcu_is_watching() fails and in_nmi() is true, > bail. > > kernel/trace/trace.c | 31 ++++++++++++++++++++++++++++++- > 1 file changed, 30 insertions(+), 1 deletion(-) > > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > index fcc9a2d..1122f15 100644 > --- a/kernel/trace/trace.c > +++ b/kernel/trace/trace.c > @@ -2568,7 +2568,36 @@ 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; > + > + if (rcu_is_watching()) { > + __ftrace_trace_stack(buffer, flags, skip, pc, NULL); > + return; > + } > + > + /* > + * When an NMI triggers, RCU is enabled via rcu_nmi_enter(), > + * but if the above rcu_is_watching() failed, then the NMI > + * triggered someplace critical, and rcu_irq_enter() should > + * not be called from NMI. > + */ > + if (unlikely(in_nmi())) > + 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_irqson(); > + __ftrace_trace_stack(buffer, flags, skip, pc, NULL); > + rcu_irq_exit_irqson(); > } > > /** > -- > 2.9.3 >