linux-kernel - Re: [PATCH][git pull] tracing: limit the number of loops the ring buffer self test can make

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Message-ID: <20090219092348.GD2354@elte.hu>
Date:	Thu, 19 Feb 2009 10:23:48 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frédéric Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH][git pull] tracing: limit the number of loops the ring
	buffer self test can make


* Steven Rostedt <rostedt@...dmis.org> wrote:

> Ingo,
> 
> I added one more fix. Thinking about the solution, although 
> the disabling of the ring buffer is good enough to prevent the 
> bug you hit. I became worried about a corrupted ring buffer 
> that can cause an inifinite loop. This patch adds a fix for 
> that too.

yes, that's a good idea too:

> @@ -23,10 +23,20 @@ static int trace_test_buffer_cpu(struct trace_array *tr, int cpu)
>  {
>  	struct ring_buffer_event *event;
>  	struct trace_entry *entry;
> +	unsigned int loops = 0;
>  
>  	while ((event = ring_buffer_consume(tr->buffer, cpu, NULL))) {
>  		entry = ring_buffer_event_data(event);
>  
> +		/*
> +		 * The ring buffer is a size of trace_buf_size, if
> +		 * we loop more than the size, there's something wrong
> +		 * with the ring buffer.
> +		 */
> +		if (loops++ > trace_buf_size) {
> +			printk(KERN_CONT ".. bad ring buffer ");
> +			goto failed;
> +		}

Would be nice to also emit a WARN_ONCE() message about the test 
failure, to make sure automated tests like mine pick even 
soft-failures up.

	Ingo
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