[RFC] per-CPU usage in perf core-book3s

[Sebastian Andrzej Siewior]

I've been looking at usage of per-CPU variable cpu_hw_events in
arch/powerpc/perf/core-book3s.c.

power_pmu_enable() and power_pmu_disable() (pmu::pmu_enable() and
pmu::pmu_disable()) are accessing the variable and the callbacks are
invoked always with disabled interrupts.

power_pmu_event_init() (pmu::event_init()) is invoked from preemptible
context and uses get_cpu_var() to obtain a stable pointer (by disabling
preemption).

pmu::pmu_enable() and pmu::pmu_disable() can be invoked via a hrtimer
(perf_mux_hrtimer_handler()) and it invokes pmu::pmu_enable() and
pmu::pmu_disable() as part of the callback.

Is there anything that prevents the timer callback to interrupt
pmu::event_init() while it is accessing per-CPU data?

Sebastian