[PATCH] lock PTE before updating it in 440/BookE page fault handler

Fix 44x and BookE page fault handler to correctly lock PTE before
trying to pte_update() it, otherwise this PTE might be swapped out
after pte_present() check but before pte_uptdate() call, resulting in
corrupted PTE. This can happen with enabled preemption and low memory
condition.

Signed-off-by: Eugene Surovegin <ebs@ebshome.net>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/ppc/mm/pgtable.c

@@ -368,7 +368,7 @@ void __init io_block_mapping(unsigned long virt, phys_addr_t phys,
  * the PTE pointer is unmodified if PTE is not found.
  */
 int
-get_pteptr(struct mm_struct *mm, unsigned long addr, pte_t **ptep)
+get_pteptr(struct mm_struct *mm, unsigned long addr, pte_t **ptep, pmd_t **pmdp)
 {
         pgd_t	*pgd;
         pmd_t	*pmd;
@@ -383,6 +383,8 @@ get_pteptr(struct mm_struct *mm, unsigned long addr, pte_t **ptep)
                         if (pte) {
 				retval = 1;
 				*ptep = pte;
+				if (pmdp)
+					*pmdp = pmd;
 				/* XXX caller needs to do pte_unmap, yuck */
                         }
                 }
@@ -420,7 +422,7 @@ unsigned long iopa(unsigned long addr)
 		mm = &init_mm;
 
 	pa = 0;
-	if (get_pteptr(mm, addr, &pte)) {
+	if (get_pteptr(mm, addr, &pte, NULL)) {
 		pa = (pte_val(*pte) & PAGE_MASK) | (addr & ~PAGE_MASK);
 		pte_unmap(pte);
 	}