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: <alpine.DEB.1.10.0902191308000.30122@gandalf.stny.rr.com>
Date:	Thu, 19 Feb 2009 13:08:37 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Ingo Molnar <mingo@...e.hu>
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



On Thu, 19 Feb 2009, Ingo Molnar wrote:

> 
> * 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.

I could put a warn on in the register_tracer code. It checks all self 
tests there, and if one fails, it disables that tracer.

-- Steve

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