linux-kernel - Re: [RFC][PATCH 03/14] arm64: function_graph: Remove use of FTRACE_NOTRACE

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Message-ID: <20181127193149.GJ5641@arm.com>
Date:   Tue, 27 Nov 2018 19:31:50 +0000
From:   Will Deacon <will.deacon@....com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Andy Lutomirski <luto@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC][PATCH 03/14] arm64: function_graph: Remove use of
 FTRACE_NOTRACE_DEPTH

Hi Steve,

On Wed, Nov 21, 2018 at 08:27:11PM -0500, Steven Rostedt wrote:
> From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
> 
> The curr_ret_stack is no longer set to -1 when not tracing a function. It is
> now done differently, and the FTRACE_NOTRACE_DEPTH value is no longer used.
> Remove the reference to it.

Do you have a pointer to the commit that changed that behaviour? I just want
to make sure we're not missing something in our unwind_frame() code.

> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will.deacon@....com>
> Cc: linux-arm-kernel@...ts.infradead.org
> Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
> ---
>  arch/arm64/kernel/stacktrace.c | 3 ---
>  1 file changed, 3 deletions(-)
> 
> diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
> index 4989f7ea1e59..7723dadf25be 100644
> --- a/arch/arm64/kernel/stacktrace.c
> +++ b/arch/arm64/kernel/stacktrace.c
> @@ -61,9 +61,6 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
>  			(frame->pc == (unsigned long)return_to_handler)) {
>  		if (WARN_ON_ONCE(frame->graph == -1))
>  			return -EINVAL;

Hmm, so is this code redundant too ^^ ?

> -		if (frame->graph < -1)
> -			frame->graph += FTRACE_NOTRACE_DEPTH;
> -

Do we still need to initialise frame->graph in __save_stack_trace()?

Will