Re: [PATCH v5 3/7] arm64: perf: Remove PMU locking

[Stephen Boyd]

Quoting Alexandru Elisei (2020-06-17 04:38:47)
> From: Julien Thierry <julien.thierry@xxxxxxx>
> 
> The PMU is disabled and enabled, and the counters are programmed from
> contexts where interrupts or preemption is disabled.
> 
> The functions to toggle the PMU and to program the PMU counters access the
> registers directly and don't access data modified by the interrupt handler.
> That, and the fact that they're always called from non-preemptible
> contexts, means that we don't need to disable interrupts or use a spinlock.

Maybe we should add a lockdep assertion that the code isn't preemptible?
I.e. add a cant_sleep() call? Or is it more that we don't need locking
because we're just doing register accesses and don't need to protect
those accesses from each other?