mm: Fix generic hugetlb pte check return type.

The include/asm-generic/hugetlb.h stubs that just vector huge_pte_*()
calls to the pte_*() implementations won't work in certain situations.

x86 and sparc, for example, return "unsigned long" from the bit
checks, and just go "return pte_val(pte) & PTE_BIT_FOO;"

But since huge_pte_*() returns 'int', if any high bits on 64-bit are
relevant, they get chopped off.

The net effect is that we can loop forever trying to COW a huge page,
because the huge_pte_write() check signals false all the time.
Reported-by: NGurudas Pai <gurudas.pai@oracle.com>
Tested-by: NGurudas Pai <gurudas.pai@oracle.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
Acked-by: NDavid Rientjes <rientjes@google.com>

include/asm-generic/hugetlb.h

@@ -6,12 +6,12 @@ static inline pte_t mk_huge_pte(struct page *page, pgprot_t pgprot)
 	return mk_pte(page, pgprot);
 }
 
-static inline int huge_pte_write(pte_t pte)
+static inline unsigned long huge_pte_write(pte_t pte)
 {
 	return pte_write(pte);
 }
 
-static inline int huge_pte_dirty(pte_t pte)
+static inline unsigned long huge_pte_dirty(pte_t pte)
 {
 	return pte_dirty(pte);
 }