linux-kernel - Re: [PATCH] ftrace: don't increment @pos in g

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Date:	Fri, 19 Jun 2009 17:45:36 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Liming Wang <liming.wang@...driver.com>
CC:	Steven Rostedt <rostedt@...dmis.org>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ftrace: don't increment @pos in g_start()

Liming Wang wrote:
> how about this one?
> 

Yeah, this should work, and cleaner than my version.

> It's wrong to increment @pos in g_start(). It causes some entries
> lost when reading set_graph_function, if the output of the file
> is large than PAGE_SIZE.
> 
> [ Impact: fix missing entries when reading set_graph_function ]
> 
> Signed-off-by: Li Zefan <lizf@...fujitsu.com>
> Signed-off-by: Liming Wang <liming.wang@...driver.com>
> ---
>  kernel/trace/ftrace.c |   14 +++++---------
>  1 files changed, 5 insertions(+), 9 deletions(-)
> 
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 134e580..1beaac6 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -2495,29 +2495,25 @@ static void *
>  g_next(struct seq_file *m, void *v, loff_t *pos)
>  {
>  	unsigned long *array = m->private;
> -	int index = *pos;
>  
> -	(*pos)++;
> +	if (v)
> +		(*pos)++;
>  
> -	if (index >= ftrace_graph_count)
> +	if (*pos >= ftrace_graph_count)
>  		return NULL;
>  
> -	return &array[index];
> +	return &array[*pos];
>  }
>  
>  static void *g_start(struct seq_file *m, loff_t *pos)
>  {
> -	void *p = NULL;
> -
>  	mutex_lock(&graph_lock);
>  
>  	/* Nothing, tell g_show to print all functions are enabled */
>  	if (!ftrace_graph_count && !*pos)
>  		return (void *)1;
>  
> -	p = g_next(m, p, pos);
> -
> -	return p;
> +	return g_next(m, NULL, pos);
>  }
>  
>  static void g_stop(struct seq_file *m, void *p)
--
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