mmotm threatens ppc preemption again

[Benjamin Herrenschmidt]

On Sun, 2011-03-20 at 19:20 -0700, Hugh Dickins wrote:
> > As long as the races to avoid are between map/unmap vs. access, yes, it
> > -should- be fine, and we used to not do demand faulting on kernel space
> > (but for how long ?). I'm wondering why we don't just stick a ptl in
> > there or is there a good reason why we can't ?
> 
> We can - but we usually prefer to avoid unnecessary locking.
> An arch function which locks init_mm.page_table_lock on powerpc,
> but does nothing on others? 

That still means gratuitous differences between how the normal and
kernel page tables are handled. Maybe that's not worth bothering ...

Cheers,
Ben.