The handling of a priority inversion between timer cancelling and a a not
well defined possible preemption of softirq kthread is not very clear.
Especially in the posix timers side it's unclear why there is a specific RT
wait callback.
All the nice explanations can be found in the initial changelog of
f61eff83ce (hrtimer: Prepare support for PREEMPT_RT").
Extract the detailed informations from there and put it into comments.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20190820132656.GC2093@lenoir
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