On Wed, Jul 10, 2013 at 08:58:11AM -0400, Steven Rostedt wrote:
> On Wed, 2013-07-10 at 14:42 +0200, Peter Zijlstra wrote:
>
> > but but but preempt_disable_notrace() isn't an rcu_read_lock().. You can only
> > do that for rcu_sched.
>
> Right. And not even rcu_sched is safe, as function tracing can trace
> functions out of rcu scope. That's why I had to add that code to do a
> schedule_on_each_cpu() in ftrace.
>
> >
> > Anyway, I don't see a nice way out of this mess :/ the entire perf core uses
> > regular RCU and converting all that is going to me a nasty big patch.
>
> There is an easier way. We can add a way to have perf not trace specific
> functions. Now there's already infrastructure there to pick and choose
> what to trace and what not to for individual function tracing users like
> perf. The trick will be how to annotate them.
>
> If there's a way to mark a function without moving it to a section, this
> would be possible. Perhaps similar to EXPORT_SYMBOL(). We could add a
> PERF_NOTRACE().
>
> static void __local_bh_enable()
> {
> [...]
> }
> PERF_NOTRACE(__local_bh_enable);
>
> And add these to a black list of functions that perf should not trace.
>
> How's that sound?
I'm afraid this is going to be hard to create and hard to keep correct :/
Other than that, a function tracer environment that is safer to use might be
useful for other people as well.
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