Re: [PATCH 02/12] powermac: support G5 CPU hotplug

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Thu, 2007-02-08 at 14:14 +0100, Johannes Berg wrote:
> On Wed, 2007-02-07 at 13:45 +0100, Johannes Berg wrote:
> 
> > Except for the in-irq count hack I'm happy with this. I still haven't found
> > where the in-hard-irq count is set to 1 in the down path during suspend or
> > resume and other platforms do similar things so I'm inclined to leave this.
> 
> Um, ok, so the hack breaks platforms that don't have paca, e.g. chrp32.
> 
> Also, I finally figured out how the in-hard-irq count happens. The thing
> is that when I try to turn off the CPU it actually doesn't really turn
> off of course, so it ends up doing NAP and taking timer interrupts...
> which goes irq_enter() and we happen to kill it afterwards.
> 
> I have two ways of fixing this:
>  - just ignore it as we do now
>  - insert a "if (cpu_dead) return" into the timer interrupt function
> 
> I prefer the latter because then we're guaranteed that whatever the
> timer interrupt does we don't modify any state for/by the CPU that isn't
> supposed to exist.

Agreed.

Ben.