Re: [for-next][PATCH 13/25] x86/mm/kmmio: Use rcu_read_lock_sched_notrace()

[Paul E. McKenney]

On Sat, Dec 10, 2022 at 05:32:27PM -0500, Steven Rostedt wrote:
> On Sat, 10 Dec 2022 13:34:12 -0800
> "Paul E. McKenney" <paulmck@xxxxxxxxxx> wrote:
> 
> > > I was going to remove it, but then I realized that it would be a functional
> > > change, as from the comment above, it uses "preempt_enable_no_resched(),
> > > which there is not a rcu_read_unlock_sched() variant.  
> > 
> > If this happens often enough, it might be worth adding something like
> > rcu_read_unlock_sched_no_resched(), but we clearly are not there yet.
> > Especially not with a name like that!  ;-)
> 
> Please don't ;-)
> 
> This is only to handle the bizarre case that mmio tracing does. Remember,
> this tracer is only for those that want to reverse engineer a binary
> driver. It's not even SMP safe! When you enable it, it shuts down all but
> one CPU. This is actually the reason I worked so hard to keep it working
> with lockdep. The shutting down of CPUs has caught so many bugs in other
> parts of the kernel! ;-)
> 
> Thus, anything that mmio tracer does, is considered niche, and not
> something to much care about.

Agreed, as I said, we are clearly not there yet.

							Thanx, Paul