From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934252AbdERPrY (ORCPT ); Thu, 18 May 2017 11:47:24 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:47422 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S933338AbdERPrP (ORCPT ); Thu, 18 May 2017 11:47:15 -0400 Date: Thu, 18 May 2017 08:47:11 -0700 From: "Paul E. McKenney" To: Steven Rostedt Cc: LKML , Ingo Molnar , Thomas Gleixner Subject: Re: [PATCH v2] tracing: Make sure RCU is watching before calling a stack trace Reply-To: paulmck@linux.vnet.ibm.com References: <20170518093809.13428efa@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170518093809.13428efa@gandalf.local.home> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 17051815-0056-0000-0000-00000368E641 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00007080; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000212; SDB=6.00862263; UDB=6.00427754; IPR=6.00641921; 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=3.00015500; XFM=3.00000015; UTC=2017-05-18 15:47:13 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17051815-0057-0000-0000-0000079F149B Message-Id: <20170518154711.GR3956@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-05-18_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=8.0.1-1703280000 definitions=main-1705180103 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 18, 2017 at 09:38:09AM -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) > --- > > Changes since v1: > > My testing discovered that the stack trace can be called with > interrupts enabled, which is a no no to have when calling > rcu_irq_enter(). When interrupts are enabled, as with being in an > NMI, RCU will also be watching. > > kernel/trace/trace.c | 26 +++++++++++++++++++++++++- > 1 file changed, 25 insertions(+), 1 deletion(-) > > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > index fcc9a2d..34a98ba 100644 > --- a/kernel/trace/trace.c > +++ b/kernel/trace/trace.c > @@ -2568,7 +2568,31 @@ 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() > + * Also, RCU is always enabled when interrupts are. > + */ > + if (!irqs_disabled() || in_nmi()) { You lost me on this one. RCU might not be watching if irqs are enabled, for example, in the idle loop. What am I missing here? Thanx, Paul > + __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 >