[PATCH] urgent rmap bugfix

It turns out there was a subtle bug in Craig Kulesa's port of
the rmap patch to 2.5, which is only apparent on non-x86 machines
where pfn 0 isn't valid.

The problem was that zap_pte_range() would clear the pte before
page_remove_rmap() would get called. This means that on these
machines the pte chain would never be removed and the machine
would oops at page_alloc.c line 98...

Thanks to Russell King for helping track down this bug.

mm/rmap.c

@@ -163,7 +163,7 @@ void page_add_rmap(struct page * page, pte_t * ptep)
 void page_remove_rmap(struct page * page, pte_t * ptep)
 {
 	struct pte_chain * pc, * prev_pc = NULL;
-	unsigned long pfn = pte_pfn(*ptep);
+	unsigned long pfn = page_to_pfn(page);
 
 	if (!page || !ptep)
 		BUG();