Re: fixing sparc64 pmap_remove_all

[Andrew Doran <ad%NetBSD.org@localhost>]

On Tue, Jan 08, 2008 at 12:37:21AM +0000, Andrew Doran wrote:
> On Mon, Jan 07, 2008 at 09:53:34PM +0100, Martin Husemann wrote:
> 
> > On Mon, Jan 07, 2008 at 09:15:55PM +0100, Tobias Nygren wrote:
> > > The problem is that the pmap refcount is set to zero in
> > > pmap_remove_all(). No other ports I checked do this.
> 
> Nice catch.
>  
> > pmap_remove_all() is an optimization to avoid a lot of work updating
> > mapping only to throw them all away later. So when we know the pmap
> > is going away (process exiting), pmap_remove_all() invalidated the
> > context, and any further pmap_remove()/pmap_page_protect()/pmap_update()
> > calls will avoid heavy work.
> > 
> > > A working solution is to cast the return value from atomic_dec_uint_nv
> > > in pmap_destroy into a signed value. This restores the previous
> > > (broken) behaviour. Maybe you guys have a better idea? :-)
> > 
> > Since pm_refs is an int I think this is the correct solution and the
> > previous behaviour is not broken at all. Andrew, what do you think?
> 
> pmap_remove_all() will only be called by the last LWP in a process
> so the refcount trick is fine, casting the return to (int) seems the
> best thing to do. I will make the change shortly.

Ok, I have checked in the fix.

Cheers,
Andrew