linux-kernel - Re: [PATCH] trace: Don't declare trace_*

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Message-ID: <20120905142623.GA19713@Krystal>
Date:	Wed, 5 Sep 2012 10:26:24 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Josh Triplett <josh@...htriplett.org>
Cc:	Steven Rostedt <rostedt@...dmis.org>, paulmck@...ux.vnet.ibm.com,
	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org, niv@...ibm.com,
	tglx@...utronix.de, peterz@...radead.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, eric.dumazet@...il.com, darren@...art.com,
	fweisbec@...il.com, sbw@....edu, patches@...aro.org,
	"Paul E. McKenney" <paul.mckenney@...aro.org>
Subject: Re: [PATCH] trace: Don't declare trace_*_rcuidle functions in modules

* Josh Triplett (josh@...htriplett.org) wrote:
> Tracepoints declare a static inline trace_*_rcuidle variant of the trace
> function, to support safely generating trace events from the idle loop.
> Module code never actually uses that variant of trace functions, because
> modules don't run code that needs tracing with RCU idled.  However, the
> declaration of those otherwise unused functions causes the module to
> reference rcu_idle_exit and rcu_idle_enter, which RCU does not export to
> modules.
> 
> To avoid this, don't generate trace_*_rcuidle functions for tracepoints
> declared in module code.
> 
> Reported-by: Steven Rostedt <rostedt@...dmis.org>
> Signed-off-by: Josh Triplett <josh@...htriplett.org>

Acked-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>

Thanks Josh!

Mathieu

> ---
> On Tue, Sep 04, 2012 at 07:46:42PM -0400, Steven Rostedt wrote:
> > We could add either. Probably keep the ugliness of tracepoints inside
> > the tracepoint code than to start spreading it around to rcu. RCU has
> > its own ugliness features ;-)
> > 
> > Hence, I would be OK if you send me a patch that does what you proposed
> > and removes the EXPORT from RCU.
> 
>  include/linux/tracepoint.h |   28 ++++++++++++++++++----------
>  1 file changed, 18 insertions(+), 10 deletions(-)
> 
> diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> index 802de56..2f322c3 100644
> --- a/include/linux/tracepoint.h
> +++ b/include/linux/tracepoint.h
> @@ -136,6 +136,22 @@ static inline void tracepoint_synchronize_unregister(void)
>  		postrcu;						\
>  	} while (0)
>  
> +#ifndef MODULE
> +#define __DECLARE_TRACE_RCU(name, proto, args, cond, data_proto, data_args)	\
> +	static inline void trace_##name##_rcuidle(proto)		\
> +	{								\
> +		if (static_key_false(&__tracepoint_##name.key))		\
> +			__DO_TRACE(&__tracepoint_##name,		\
> +				TP_PROTO(data_proto),			\
> +				TP_ARGS(data_args),			\
> +				TP_CONDITION(cond),			\
> +				rcu_idle_exit(),			\
> +				rcu_idle_enter());			\
> +	}
> +#else
> +#define __DECLARE_TRACE_RCU(name, proto, args, cond, data_proto, data_args)
> +#endif
> +
>  /*
>   * Make sure the alignment of the structure in the __tracepoints section will
>   * not add unwanted padding between the beginning of the section and the
> @@ -151,16 +167,8 @@ static inline void tracepoint_synchronize_unregister(void)
>  				TP_ARGS(data_args),			\
>  				TP_CONDITION(cond),,);			\
>  	}								\
> -	static inline void trace_##name##_rcuidle(proto)		\
> -	{								\
> -		if (static_key_false(&__tracepoint_##name.key))		\
> -			__DO_TRACE(&__tracepoint_##name,		\
> -				TP_PROTO(data_proto),			\
> -				TP_ARGS(data_args),			\
> -				TP_CONDITION(cond),			\
> -				rcu_idle_exit(),			\
> -				rcu_idle_enter());			\
> -	}								\
> +	__DECLARE_TRACE_RCU(name, PARAMS(proto), PARAMS(args),		\
> +		PARAMS(cond), PARAMS(data_proto), PARAMS(data_args))	\
>  	static inline int						\
>  	register_trace_##name(void (*probe)(data_proto), void *data)	\
>  	{								\
> -- 
> 1.7.10.4
> 

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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