Re: [PATCH 0/11 v2] Use local_lock for pcp protection and reduce stat overhead

[Peter Zijlstra]

On Wed, Apr 07, 2021 at 09:24:12PM +0100, Mel Gorman wrote:
> Why local_lock? PREEMPT_RT considers the following sequence to be unsafe
> as documented in Documentation/locking/locktypes.rst
> 
>    local_irq_disable();
>    raw_spin_lock(&lock);

Almost, the above is actually OK on RT. The problematic one is:

	local_irq_disable();
	spin_lock(&lock);

That doesn't work on RT since spin_lock() turns into a PI-mutex which
then obviously explodes if it tries to block with IRQs disabled.

And it so happens, that's exactly the one at hand.