diff --git a/[refs] b/[refs]
index e6c74afb13d7..3acec5d75cdd 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 6c6d5280431544e4036886ea74e3334a98bc5f96
+refs/heads/master: c27fe4c8942d3ca715986f79cc26f44608d7d9fb
diff --git a/trunk/include/linux/mm.h b/trunk/include/linux/mm.h
index 6321e840e21d..3c5505a3bc49 100644
--- a/trunk/include/linux/mm.h
+++ b/trunk/include/linux/mm.h
@@ -911,6 +911,8 @@ unsigned long unmap_vmas(struct mmu_gather *tlb,
  * @pte_entry: if set, called for each non-empty PTE (4th-level) entry
  * @pte_hole: if set, called for each hole at all levels
  * @hugetlb_entry: if set, called for each hugetlb entry
+ *		   *Caution*: The caller must hold mmap_sem() if @hugetlb_entry
+ * 			      is used.
  *
  * (see walk_page_range for more details)
  */
diff --git a/trunk/mm/pagewalk.c b/trunk/mm/pagewalk.c
index ee4ff87c58c1..f7929406e776 100644
--- a/trunk/mm/pagewalk.c
+++ b/trunk/mm/pagewalk.c
@@ -181,6 +181,9 @@ static int walk_hugetlb_range(struct vm_area_struct *vma,
  *
  * If any callback returns a non-zero value, the walk is aborted and
  * the return value is propagated back to the caller. Otherwise 0 is returned.
+ *
+ * walk->mm->mmap_sem must be held for at least read if walk->hugetlb_entry
+ * is !NULL.
  */
 int walk_page_range(unsigned long addr, unsigned long end,
 		    struct mm_walk *walk)