diff --git a/mm/slab.c b/mm/slab.c
index a041c53..05a3910 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -2998,6 +2998,8 @@
  * kfree - free previously allocated memory
  * @objp: pointer returned by kmalloc.
  *
+ * If @objp is NULL, no operation is performed.
+ *
  * Don't free memory not originally allocated by kmalloc()
  * or you will run into trouble.
  */
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 67b358e..13c3d82 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -332,9 +332,10 @@
  *	@addr:		memory base address
  *
  *	Free the virtually contiguous memory area starting at @addr, as
- *	obtained from vmalloc(), vmalloc_32() or __vmalloc().
+ *	obtained from vmalloc(), vmalloc_32() or __vmalloc(). If @addr is
+ *	NULL, no operation is performed.
  *
- *	May not be called in interrupt context.
+ *	Must not be called in interrupt context.
  */
 void vfree(void *addr)
 {
@@ -352,7 +353,7 @@
  *	Free the virtually contiguous memory area starting at @addr,
  *	which was created from the page array passed to vmap().
  *
- *	May not be called in interrupt context.
+ *	Must not be called in interrupt context.
  */
 void vunmap(void *addr)
 {