linux-kernel - Re: Another RCU trace. (3.10-rc5)

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Message-ID: <1370903137.9844.133.camel@gandalf.local.home>
Date:	Mon, 10 Jun 2013 18:25:37 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>, fweisbec@...il.com
Subject: Re: Another RCU trace. (3.10-rc5)

On Mon, 2013-06-10 at 15:10 -0700, Paul E. McKenney wrote:

> > So maybe that patch was a winner after all and got dropped ?
> 
> Please see below for the patch that I was thinking of.
> 
> It has not been dropped, I was on travel and a bit slow about pushing
> things.
> 
> 							Thanx, Paul
> 
> ------------------------------------------------------------------------
> 
> trace: Allow idle-safe tracepoints to be called from irq
> 
> __DECLARE_TRACE_RCU() currently creates an _rcuidle() tracepoint which
> may safely be invoked from what RCU considers to be an idle CPU.
> However, these _rcuidle() tracepoints may -not- be invoked from the
> handler of an irq taken from idle, because rcu_idle_enter() zeroes
> RCU's nesting-level counter, so that the rcu_irq_exit() returning to
> idle will trigger a WARN_ON_ONCE().
> 
> This commit therefore substitutes rcu_irq_enter() for rcu_idle_exit()
> and rcu_irq_exit() for rcu_idle_enter() in order to make the _rcuidle()
> tracepoints usable from irq handlers as well as from process context.
> 
> Reported-by: Dave Jones <davej@...hat.com>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> 
> diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> index 2f322c3..f8e084d 100644
> --- a/include/linux/tracepoint.h
> +++ b/include/linux/tracepoint.h
> @@ -145,8 +145,8 @@ static inline void tracepoint_synchronize_unregister(void)
>  				TP_PROTO(data_proto),			\
>  				TP_ARGS(data_args),			\
>  				TP_CONDITION(cond),			\
> -				rcu_idle_exit(),			\
> -				rcu_idle_enter());			\
> +				rcu_irq_enter(),			\
> +				rcu_irq_exit());			\

Still wont fix the splat that Dave saw. As the splat has nothing to do
with tracepoints, but has to do with function tracing, which is a whole
'nother beast.

-- Steve

>  	}
>  #else
>  #define __DECLARE_TRACE_RCU(name, proto, args, cond, data_proto, data_args)


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