linux-kernel - Re: [RFA][PATCH 25/27] arm64, ftrace: Remove check of obsolete variable function_trace

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Date:	Fri, 27 Jun 2014 13:44:21 +0100
From:	Will Deacon <will.deacon@....com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	"linux-kernel@...r.kernel.org" <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" <linux-arch@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Jiri Kosina <jkosina@...e.cz>,
	Josh Poimboeuf <notifications@...hub.com>,
	AKASHI Takahiro <takahiro.akashi@...aro.org>
Subject: Re: [RFA][PATCH 25/27] arm64, ftrace: Remove check of obsolete
 variable function_trace_stop

Hi Steve,

On Thu, Jun 26, 2014 at 05:52:46PM +0100, Steven Rostedt wrote:
> From: "Steven Rostedt (Red Hat)" <rostedt@...dmis.org>
> 
> Nothing sets function_trace_stop to disable function tracing anymore.
> Remove the check for it in the arch code.
> 
> arm64 was broken anyway, as it had an ifdef testing
>  CONFIG_HAVE_FUNCTION_TRACE_MCOUNT_TEST which is only set if
> the arch supports the code (which it obviously did not), and
> it was testing a non existent ftrace_trace_stop instead of
> function_trace_stop.

Yeah, the current code is total crap. Well spotted.

> Cc: AKASHI Takahiro <takahiro.akashi@...aro.org>
> Cc: Will Deacon <will.deacon@....com>
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
> ---
>  arch/arm64/kernel/entry-ftrace.S | 5 -----
>  1 file changed, 5 deletions(-)

  Acked-by: Will Deacon <will.deacon@....com>

I'm happy for you to take this via the ftrace tree, along with the rest of
the series.

I successfully ran the ftrace self tests with this applied (on top of
"ftrace: Remove check for HAVE_FUNCTION_TRACE_MCOUNT_TEST"), but note
that I don't have a platform with working suspend/resume right now.

Cheers,

Will

> diff --git a/arch/arm64/kernel/entry-ftrace.S b/arch/arm64/kernel/entry-ftrace.S
> index b051871f2965..1b1e330e6849 100644
> --- a/arch/arm64/kernel/entry-ftrace.S
> +++ b/arch/arm64/kernel/entry-ftrace.S
> @@ -96,11 +96,6 @@
>   *     - ftrace_graph_caller to set up an exit hook
>   */
>  ENTRY(_mcount)
> -#ifdef CONFIG_HAVE_FUNCTION_TRACE_MCOUNT_TEST
> -	ldr	x0, =ftrace_trace_stop
> -	ldr	x0, [x0]		// if ftrace_trace_stop
> -	ret				//   return;
> -#endif
>  	mcount_enter
>  
>  	ldr	x0, =ftrace_trace_function
> -- 
> 2.0.0
> 
> 
> 
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