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SubjectRe: [PATCH 2/3] trace: fix default boot up tracer
On Mon, 2 Feb 2009 23:33:52 -0500 (EST) Steven Rostedt <rostedt@goodmis.org> wrote:

> On Mon, 2 Feb 2009, Andrew Morton wrote:
> > >
> > > The lock_kernel addition was added when the BKL became a spinlock again.
> > > The selftests needed to be able to sleep, and this caused issues.
> >
> > Sleeping inside lock_kernel() is quite OK. Confused.
>
> I did not explain that quite well. I need to focus on the emails
> that I write, and not do it half concentrating on code that I'm
> also writing :-/
>
> The preempt tracer expects preemption enabled when the self test is
> executed. Because the self test for preempt tracer is basically:
>
> start_trace();
> preempt_disable();
> udelay(x);
> preempt_enable();
> stop_trace();
>
> make sure we have a delay.
>
> This failed, because lock_kernel now disables preemption. So that
> preempt_disable() never triggers the trace, and the test sees that nothing
> was recorded. This causes a failure to be flagged, and we disable the
> preempt tracer.

OK.

It might be a bit cleaner to run all the selftests later, after
start_kernel() has done unlock_kernel(). That would make it even
harder to support modular tracers in the future though.

Perhaps the preempt tracer could itself do

if (kernel_locked()) {
kernel_was_locked = true;
unlock_kernel();
}
...


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