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SubjectRe: [PATCH] tracing, sched: mark preempt_schedule() notrace


On Tue, 18 Aug 2009, Frederic Weisbecker wrote:

> On Tue, Aug 18, 2009 at 04:01:57PM +0800, Lai Jiangshan wrote:
> >
> > Current preempt_schedule() is not marked notrace. It may be
> > infinite recursion in __trace_graph_return().
> >
> > preempt_schedule()
> > __trace_graph_return()
> > ftrace_preempt_disable() (!!return false!!)
> > ftrace_preempt_enable()
> > preempt_enable_notrace()
> > preempt_schedule() (need_resched() may be true again)
>
>
>
> It would happen in __trace_graph_return() , when preempt_schedule()
> has finished its job. It's very unlikely the TIF_NEED_RESCHED is
> set just after (because it has just been cleared).
> But why not. In that case, preempt_schedule() is called again but it's
> not a real tracing recursion.
>
> That seems like a normal behaviour actually.

In fact, this is actually something to be traced. I would not add a
notrace to it. This is not saving anything, the trace_graph_return does
not need to worry about stack overflow, since the return code already
freed the stack.

-- Steve


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