From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932689AbdEROup (ORCPT ); Thu, 18 May 2017 10:50:45 -0400 Received: from mail.kernel.org ([198.145.29.99]:47278 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932406AbdEROuo (ORCPT ); Thu, 18 May 2017 10:50:44 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D7D3B239BA Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=rostedt@goodmis.org Date: Thu, 18 May 2017 10:50:41 -0400 From: Steven Rostedt To: "Paul E. McKenney" Cc: LKML , Ingo Molnar , Thomas Gleixner Subject: Re: [PATCH v2] tracing: Make sure RCU is watching before calling a stack trace Message-ID: <20170518105041.54005899@gandalf.local.home> In-Reply-To: <20170518093809.13428efa@gandalf.local.home> References: <20170518093809.13428efa@gandalf.local.home> X-Mailer: Claws Mail 3.14.0 (GTK+ 2.24.31; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 18 May 2017 09:38:09 -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" Paul, Can you give me an ack for this version too. Thanks! -- Steve > 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()) { > + __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(); > } > > /**