Re: [PATCH v2] rcu/nocb: Handle concurrent nocb kthreads creation

[Frederic Weisbecker]

On Mon, Dec 13, 2021 at 11:28:45AM +0000, David Woodhouse wrote:
> On Mon, 2021-12-13 at 12:22 +0100, Frederic Weisbecker wrote:
> > I was about to ack the patch but, should we really add code that isn't going to
> > be necessary before a long while?
> 
> Yeah, I'm torn on that. In this case it's harmless enough and it makes
> the code reentrant in its own right instead of relying on the fact that
> the cpuhp code won't invoke it multiple times in parallel. So I think
> that's reasonable defensive programming.
> 

The thing is that RCU code is already quite complicated. Are we even at least
sure that we'll ever make CPU hotplug allow concurrent CPU onlining/offlining?

This will require much more thoughts and a new hotplug concurrency
infrastructure that we'll need to base RCU on. IMHO it's a bit early to handle
that on hotplug individual callbacks.

But anyway, let's see what Paul thinks about it...