mmotm threatens ppc preemption again

[Hugh Dickins]

On Mon, 21 Mar 2011, Benjamin Herrenschmidt 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?

Hugh