hugetlb: handle write-protection faults in follow_hugetlb_page

The follow_hugetlb_page() fix I posted (merged as git commit 5b23dbe8173c212d6a326e35347b038705603d39) missed one case. If the pte is present, but not writable and write access is requested by the caller to get_user_pages(), the code will do the wrong thing. Rather than calling hugetlb_fault to make the pte writable, it notes the presence of the pte and continues.

This simple one-liner makes sure we also fault on the pte for this case. Please apply.

---

 mm/hugetlb.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

index 6121b57..6f97821 100644
@@ -907,7 +907,7 @@ int follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
 		 */
 		pte = huge_pte_offset(mm, vaddr & HPAGE_MASK);
 
-		if (!pte || pte_none(*pte)) {
+		if (!pte || pte_none(*pte) || (write && !pte_write(*pte))) {
 			int ret;
 
 			spin_unlock(&mm->page_table_lock);