adding symetric test case for change_page_attr

["William Morrow" <William.Morrow@xxxxxxx>]

Hi,

This is just a suggested patch for arch/i386/mm/pageattr.c

I was fooled into thinking that there was a problem with caching using
change_page_attr(virt_to_page(address),1,PAGE_KERNEL);
because if the page is already PAGE_KERNEL, it incorrectly decrements 
the count field.
In the case of using
change_page_attr(virt_to_page(address),1,PAGE_KERNEL_NOCACHE);
if the page is already not cached, the count is handled correctly.
The patch applies the same logic for the symmetric case.

The same logic should be used in the other architectures to prevent this 
problem.

morrow

*** pageattr.c.orig	2004-12-21 15:29:35.000000000 -0700
--- pageattr.c	2004-12-21 15:41:53.000000000 -0700
***************
*** 130,137 ****
  			set_pmd_pte(kpte,address,mk_pte(split, PAGE_KERNEL));
  		}	
  	} else if ((pte_val(*kpte) & _PAGE_PSE) == 0) { 
! 		set_pte_atomic(kpte, mk_pte(page, PAGE_KERNEL));
! 		__put_page(kpte_page);
  	}
  
  	if (cpu_has_pse && (page_count(kpte_page) == 1)) {
--- 130,141 ----
  			set_pmd_pte(kpte,address,mk_pte(split, PAGE_KERNEL));
  		}	
  	} else if ((pte_val(*kpte) & _PAGE_PSE) == 0) { 
! 		pte_t old = *kpte;
! 		pte_t standard = mk_pte(page, PAGE_KERNEL); 
! 		if (!pte_same(old,standard)) {
! 			set_pte_atomic(kpte, standard);
! 			__put_page(kpte_page);
! 		}
  	}
  
  	if (cpu_has_pse && (page_count(kpte_page) == 1)) {