diff --git a/include/linux/mm.h b/include/linux/mm.h
index 6321e84..3c5505a 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -911,6 +911,8 @@
  * @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/mm/pagewalk.c b/mm/pagewalk.c
index ee4ff87..f792940 100644
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -181,6 +181,9 @@
  *
  * 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)