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.

Signed-off-by: Adam Litke <agl@us.ibm.com>
Acked-by: Dave Kleikamp <shaggy@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 6121b57bbe96..6f978218c2c8 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -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);