[PATCH] i386 pgd_index() doesn't parenthesize its arg

Patch from William Lee Irwin III <wli@holomorphy.com>

pgd_index() doesn't parenthesize its argument.  This is a bad idea for
macros, since it's legitimate to pass expressions to them that will get
misinterpreted given operator precedence and the shift.

include/asm-i386/pgtable.h

@@ -242,7 +242,7 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
 	((pmd_val(pmd) & (_PAGE_PSE|_PAGE_PRESENT)) == (_PAGE_PSE|_PAGE_PRESENT))
 
 /* to find an entry in a page-table-directory. */
-#define pgd_index(address) ((address >> PGDIR_SHIFT) & (PTRS_PER_PGD-1))
+#define pgd_index(address) (((address) >> PGDIR_SHIFT) & (PTRS_PER_PGD-1))
 
 #define __pgd_offset(address) pgd_index(address)