[PATCH 1/3] arm64: perf: Make PMU interrupt NMI safe

[Peter Zijlstra]

On Wed, Jan 17, 2018 at 12:04:43PM +0000, Julien Thierry wrote:
> Before using an NMI, we must make sure the IRQ handler uses no locks and
> only calls NMI safe functions.
> 
> Get rid of PMU lock, saving and restoring the PMU counter selector in the
> PMU interrupt handler

You fail to explain why its safe to do so. Presumably that lock was
there for a reason, why can you remove it and expect things to keep
working?