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Re: [PATCH 7/5] tracing: Make sure rcu_irq_enter() can work for trace_*_rcuidle() trace events

From Steven Rostedt <rostedt@goodmis.org>
Newsgroups linux.kernel
Subject Re: [PATCH 7/5] tracing: Make sure rcu_irq_enter() can work for trace_*_rcuidle() trace events
Date 2017-04-07 19:30 +0200
Message-ID <ttFRT-1SP-1@gated-at.bofh.it> (permalink)
References <ttCKl-8a9-13@gated-at.bofh.it> <ttFyx-1Kj-3@gated-at.bofh.it> <ttFIe-1OF-15@gated-at.bofh.it>
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On Fri, 7 Apr 2017 17:19:05 +0000 (UTC)
Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote:

> ----- On Apr 7, 2017, at 1:06 PM, rostedt rostedt@goodmis.org wrote:
> 
> > From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
> > 
> > Stack tracing discovered that there's a small location inside the RCU
> > infrastructure that calling rcu_irq_enter() does not work. As trace events  
> 
> that -> where

ok

> 
> Do you have a link to the lkml thread where this stack tracing discovery
> happened ?

Actually it's this thread. But here:

Version 1 of the patch series:
 http://lkml.kernel.org/r/20170406164237.874767449@goodmis.org

Version 2 of the patch series:
 http://lkml.kernel.org/r/20170407140106.051135969@goodmis.org

> 
> > use rcu_irq_enter() it must make sure that it is functionable. A check  
> 
> I don't think functionable is the word you are looking for here. Perhaps
> "must make sure that it can be invoked" ?
> 
> > against rcu_irq_enter_disabled() is added with a WARN_ON_ONCE() as no trace
> > event should ever be used in that part of RCU. If the warning is triggered,
> > then the trace event is ignored.
> > 
> > Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> > Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
> > ---
> > include/linux/tracepoint.h | 2 ++
> > 1 file changed, 2 insertions(+)
> > 
> > diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> > index f72fcfe..8baef96 100644
> > --- a/include/linux/tracepoint.h
> > +++ b/include/linux/tracepoint.h
> > @@ -159,6 +159,8 @@ extern void syscall_unregfunc(void);
> > 				TP_PROTO(data_proto),			\
> > 				TP_ARGS(data_args),			\
> > 				TP_CONDITION(cond),			\
> > +				if (WARN_ON_ONCE(rcu_irq_enter_disabled())) \
> > +					return;				\  
> 
> I must admit that it's a bit odd to have:
> 
> if (WARN_ON_ONCE(rcu_irq_enter_disabled()))
>        return;
> rcu_irq_enter_irqson()

Welcome to MACRO MAGIC!

> 
> as one argument to the __DO_TRACE() macro. To me it's a bit unexpected
> coding-style wise. Am I the only one not comfortable with the proposed
> syntax ?

The entire TRACE_EVENT()/__DO_TRACE() is special.

I thought about add yet another parameter, but as it doesn't change
much, I figured this was good enough. We could beak it up if you like:

#define RCU_IRQ_ENTER_CHECK \
	if (WARN_ON_ONCE(rcu_irq_enter_disabled()) 	\
		return;					\
	rcu_irq_enter_irqson();

[..]
			__DO_TRACE(&__tracepoint_##name,		\
				TP_PROTO(data_proto),			\
				TP_ARGS(data_args),			\
				TP_CONDITION(cond),			\
				PARAMS(RCU_IRQ_ENTER_CHECK),		\
				rcu_irq_exit_irqson());			\


Would that make you feel more comfortable?

-- Steve

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Thread

[PATCH 0/5 v2] tracing: Add usecase of synchronize_rcu_tasks() and stack_tracer_disable() Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 16:10 +0200
  [PATCH 1/5 v2] ftrace: Add use of synchronize_rcu_tasks() with dynamic trampolines Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 16:10 +0200
  [PATCH 3/5 v2] tracing: Add stack_tracer_disable/enable() functions Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 16:10 +0200
    [PATCH 3/5 v2.1] tracing: Add stack_tracer_disable/enable()  functions Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 16:30 +0200
    Re: [PATCH 3/5 v2] tracing: Add stack_tracer_disable/enable()  functions Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 16:30 +0200
  Re: [PATCH 0/5 v2] tracing: Add usecase of synchronize_rcu_tasks()  and stack_tracer_disable() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-04-07 16:50 +0200
    Re: [PATCH 0/5 v2] tracing: Add usecase of synchronize_rcu_tasks()  and stack_tracer_disable() Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 17:10 +0200
      Re: [PATCH 0/5 v2] tracing: Add usecase of synchronize_rcu_tasks()  and stack_tracer_disable() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-04-07 17:20 +0200
        Re: [PATCH 0/5 v2] tracing: Add usecase of synchronize_rcu_tasks()  and stack_tracer_disable() Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 17:30 +0200
  [PATCH 6/5]rcu/tracing: Add rcu_disabled to denote when  rcu_irq_enter() will not work Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 18:40 +0200
    Re: [PATCH 6/5]rcu/tracing: Add rcu_disabled to denote when  rcu_irq_enter() will not work "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-04-07 18:50 +0200
      Re: [PATCH 6/5]rcu/tracing: Add rcu_disabled to denote when  rcu_irq_enter() will not work Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 18:50 +0200
        Re: [PATCH 6/5]rcu/tracing: Add rcu_disabled to denote when  rcu_irq_enter() will not work "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-04-07 19:00 +0200
      [PATCH 6/5 v2] rcu/tracing: Add rcu_disabled to denote when  rcu_irq_enter() will not work Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 19:10 +0200
        Re: [PATCH 6/5 v2] rcu/tracing: Add rcu_disabled to denote when  rcu_irq_enter() will not work "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-04-07 19:20 +0200
  [PATCH 7/5] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 19:10 +0200
    Re: [PATCH 7/5] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-04-07 19:20 +0200
    Re: [PATCH 7/5] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2017-04-07 19:20 +0200
      Re: [PATCH 7/5] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 19:30 +0200
        Re: [PATCH 7/5] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 19:40 +0200
        Re: [PATCH 7/5] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2017-04-07 19:50 +0200
          Re: [PATCH 7/5] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 20:00 +0200
          [PATCH 7/5 v3] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 20:20 +0200
            Re: [PATCH 7/5 v3] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2017-04-07 20:20 +0200
              Re: [PATCH 7/5 v4] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 21:50 +0200
              [PATCH 7/5 v4] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 21:50 +0200
      Re: [PATCH 7/5] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 19:30 +0200
      [PATCH 7/5 v2] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 19:50 +0200

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