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SubjectRe: [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@goodmis.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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