Re: [PATCH] notifier: Make atomic_notifiers use raw_spinlock

[Peter Zijlstra]

On Fri, Aug 06, 2021 at 08:06:53PM +0200, Sebastian Andrzej Siewior wrote:
> On 2021-08-06 20:02:42 [+0200], Peter Zijlstra wrote:
> > On Fri, Aug 06, 2021 at 04:07:18PM +0200, Sebastian Andrzej Siewior wrote:
> > > What do we do with this?
> > > Do we merge this as-is, add another "robust atomic notifier" using only
> > > raw_spinlock_t for registration and notification (for only
> > > cpu_pm_notifier_chain) instead of switching to raw_spinlock_t for all
> > > atomic notifier in -tree?
> > 
> > Right, so the problem I see with this is that
> > notifier_chain_{,un}register() are O(n). Hardly something we should be
> > putting under raw_spin_lock :/
> 
> Yup, pretty much. So we make one robust notifier for
> cpu_pm_notifier_chain?

Yeah, I suppose so :-( Ideally that whole pm notifier thing goes, but
that's *far* more work and I really don't want to be responsible for the
brain damange resulting from looking at all that 'special' idle code.