linux-kernel - Re: [PATCH] function_graph: remove unnecessary initialization in ftrace_graph_ret

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Message-ID: <20240916123925.5398abdf@rorschach.local.home>
Date: Mon, 16 Sep 2024 12:39:25 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Oleg Nesterov <oleg@...hat.com>
Cc: Masami Hiramatsu <mhiramat@...nel.org>, Puranjay Mohan
 <puranjay@...nel.org>, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH] function_graph: remove unnecessary initialization in
 ftrace_graph_ret_addr()

On Mon, 16 Sep 2024 15:56:43 +0200
Oleg Nesterov <oleg@...hat.com> wrote:

> After the commit 29c1c24a2707 ("function_graph: Fix up ftrace_graph_ret_addr()")
> ftrace_graph_ret_addr() doesn't need to initialize "int i" at the start.
> 
> While at it, move the declaration of "ret_stack" into the main loop.

Should not make two changes like this, because it risks the entire
patch being denied.


> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> ---
>  kernel/trace/fgraph.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
> index d7d4fb403f6f..d45a8bc97997 100644
> --- a/kernel/trace/fgraph.c
> +++ b/kernel/trace/fgraph.c
> @@ -890,9 +890,8 @@ ftrace_graph_get_ret_stack(struct task_struct *task, int idx)
>  unsigned long ftrace_graph_ret_addr(struct task_struct *task, int *idx,
>  				    unsigned long ret, unsigned long *retp)
>  {
> -	struct ftrace_ret_stack *ret_stack;
>  	unsigned long return_handler = (unsigned long)dereference_kernel_function_descriptor(return_to_handler);
> -	int i = task->curr_ret_stack;
> +	int i;

I'm fine with removing the unneeded init of i.

>  
>  	if (ret != return_handler)
>  		return ret;
> @@ -902,7 +901,7 @@ unsigned long ftrace_graph_ret_addr(struct task_struct *task, int *idx,
>  
>  	i = *idx ? : task->curr_ret_stack;
>  	while (i > 0) {
> -		ret_stack = get_ret_stack(task, i, &i);
> +		struct ftrace_ret_stack *ret_stack = get_ret_stack(task, i, &i);

This is just a preference. Sometimes I like the declaration up on top,
sometimes in the block it used. But this case, I wont it at top.

Please make a v2 with just the change to i.

-- Steve


>  		if (!ret_stack)
>  			break;
>  		/*