linux-kernel - Re: [RFA][PATCH 09/27] powerpc/ftrace: Add call to ftrace_graph_is

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Message-ID: <20140709100453.689b1ef6@gandalf.local.home>
Date:	Wed, 9 Jul 2014 10:04:53 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	"H. Peter Anvin" <hpa@...or.com>, linux-arch@...r.kernel.org,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Jiri Kosina <jkosina@...e.cz>,
	Josh Poimboeuf <notifications@...hub.com>,
	Anton Blanchard <anton@...ba.org>
Subject: Re: [RFA][PATCH 09/27] powerpc/ftrace: Add call to
 ftrace_graph_is_dead() in function graph code

Ben,

Can you ack this please?

Thanks,

-- Steve


On Thu, 26 Jun 2014 12:52:30 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> From: "Steven Rostedt (Red Hat)" <rostedt@...dmis.org>
> 
> ftrace_stop() is going away as it disables parts of function tracing
> that affects users that should not be affected. But ftrace_graph_stop()
> is built on ftrace_stop(). Here's another example of killing all of
> function tracing because something went wrong with function graph
> tracing.
> 
> Instead of disabling all users of function tracing on function graph
> error, disable only function graph tracing. To do this, the arch code
> must call ftrace_graph_is_dead() before it implements function graph.
> 
> Cc: Anton Blanchard <anton@...ba.org>
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
> ---
>  arch/powerpc/kernel/ftrace.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/powerpc/kernel/ftrace.c b/arch/powerpc/kernel/ftrace.c
> index f202d0731b06..f8c0ce5523a5 100644
> --- a/arch/powerpc/kernel/ftrace.c
> +++ b/arch/powerpc/kernel/ftrace.c
> @@ -527,6 +527,9 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)
>  	struct ftrace_graph_ent trace;
>  	unsigned long return_hooker = (unsigned long)&return_to_handler;
>  
> +	if (unlikely(ftrace_graph_is_dead()))
> +		return;
> +
>  	if (unlikely(atomic_read(&current->tracing_graph_pause)))
>  		return;
>  

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