linux-kernel - Re: [PATCH 3/5] tracing/events: add rcu locking around trace event prints

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Date:	Fri, 17 Apr 2009 10:08:57 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Theodore Tso <tytso@....edu>
cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Subject: Re: [PATCH 3/5] tracing/events: add rcu locking around trace event
 prints


Ted, is this patch still needed?

I'm starting to have second thoughts on this patch because it may require 
adding: #include <linux/rcupdate.h> in include/trace/ftrace.h. Jeremy has 
been struggling with include hell with these files.

Hmm, maybe this is not an issue because we undef CREATE_TRACE_POINTS 
before calling this.

Jeremy,

Do you see a problem if we include linux/rcupdate.h in ftrace.h?
Remember, CREATE_TRACE_POINTS is undefined here.

Thanks,

-- Steve


On Wed, 15 Apr 2009, Steven Rostedt wrote:

> From: Steven Rostedt <srostedt@...hat.com>
> 
> Some trace events need to have a way to print out data that his
> allocated, but will be freed later. Using a function that can allocate
> memory, and free it with call_rcu, can be useful.
> 
> This patch adds rcu locking around the print part of the TRACE_EVENT
> macro to facilitate this.
> 
> Reported-by: Theodore Tso <tytso@....edu>
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
> ---
>  include/trace/ftrace.h |    4 ++++
>  1 files changed, 4 insertions(+), 0 deletions(-)
> 
> diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
> index 60c5323..6fb06bd 100644
> --- a/include/trace/ftrace.h
> +++ b/include/trace/ftrace.h
> @@ -62,7 +62,9 @@
>   *
>   *	field = (typeof(field))entry;
>   *
> + *	rcu_read_lock();
>   *	ret = trace_seq_printf(s, <TP_printk> "\n");
> + *	rcu_read_unlock();
>   *	if (!ret)
>   *		return TRACE_TYPE_PARTIAL_LINE;
>   *
> @@ -99,7 +101,9 @@ ftrace_raw_output_##call(struct trace_iterator *iter, int flags)	\
>  									\
>  	field = (typeof(field))entry;					\
>  									\
> +	rcu_read_lock();						\
>  	ret = trace_seq_printf(s, #call ": " print);			\
> +	rcu_read_unlock();						\
>  	if (!ret)							\
>  		return TRACE_TYPE_PARTIAL_LINE;				\
>  									\
> -- 
> 1.6.2.1
> 
> -- 
> 
--
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