linux-kernel - Re: ftrace does not work on cpus

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Date:	Sat, 16 Oct 2010 11:17:52 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Robin Holt <holt@....com>, Ingo Molnar <mingo@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: ftrace does not work on cpus > 999.

On Sat, 2010-10-16 at 16:45 +0200, Frederic Weisbecker wrote:

> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 9ec59f5..3565f9e 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -3999,7 +3999,7 @@ static void tracing_init_debugfs_percpu(long cpu)
>  	/* strlen(cpu) + MAX(log10(cpu)) + '\0' */
>  	char cpu_dir[7];
>  
> -	if (cpu > 999 || cpu < 0)
> +	if (cpu < 0)
>  		return;
>  
>  	sprintf(cpu_dir, "cpu%ld", cpu);

You need to change the size of cpu_dir, otherwise this will overflow.

The other case is to dynamically allocate cpu_dir.

	char *cpu_dir;
	int count = cpu;
	int size;

	if (cpu < 0)
		return;

	/* log10 sizeof cpu */
	for (size = 0; count > 0; count /= 10, size++)
		;

	cpu_dir = kmalloc(size + 4, GFP_KERNEL);

	if (!cpu_dir)
		return;

	snprintf(cpu_dir, size + 4, "cpu%ld", cpu);

	[...]

	kfree(cpu_dir);

-- Steve


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