linux-kernel - Re: [PATCH] ftrace: unsigned idx cannot be less than 0

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Message-ID: <20090102154805.GA6833@nowhere>
Date:	Fri, 2 Jan 2009 16:48:06 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Roel Kluin <roel.kluin@...il.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	lkml <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] ftrace: unsigned idx cannot be less than 0

On Fri, Jan 02, 2009 at 03:49:43PM +0100, Roel Kluin wrote:
> // vi kernel/trace/ftrace.c +787
> struct ftrace_iterator {
> ...
>         unsigned                idx;
> ...
> };
> 
> idx is unsigned and cannot be less than 0.
> 
> Signed-off-by: Roel Kluin <roel.kluin@...il.com>
> ---
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 2f32969..a344add 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -842,7 +842,7 @@ static void *t_start(struct seq_file *m, loff_t *pos)
>  	void *p = NULL;
>  
>  	if (*pos > 0) {
> -		if (iter->idx < 0)
> +		if (iter->idx == 0)
>  			return p;
>  		(*pos)--;
>  		iter->idx--;


Hi Roel,

I'm not sure this is the right fix.
If you look at t_next, if there is no more page to look at,
iter_idx takes -1.

A 0 value would mean: we are in the first index on the page, which means
there is something to read and we don't want to return NULL.

I guess that would be better to turn idx into a signed int.

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