1 files changed, 10 insertions, 4 deletions

diff --git a/kernel/futex.c b/kernel/futex.c
index f3a3a071283c..bbf071f325b8 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -143,9 +143,8 @@
  *
  * Where (A) orders the waiters increment and the futex value read through
  * atomic operations (see hb_waiters_inc) and where (B) orders the write
- * to futex and the waiters read -- this is done by the barriers in
- * get_futex_key_refs(), through either ihold or atomic_inc, depending on the
- * futex type.
+ * to futex and the waiters read -- this is done by the barriers for both
+ * shared and private futexes in get_futex_key_refs().
  *
  * This yields the following case (where X:=waiters, Y:=futex):
  *
@@ -344,13 +343,20 @@ static void get_futex_key_refs(union futex_key *key)
                 futex_get_mm(key); /* implies MB (B) */
                 break;
         default:
+                /*
+                 * Private futexes do not hold reference on an inode or
+                 * mm, therefore the only purpose of calling get_futex_key_refs
+                 * is because we need the barrier for the lockless waiter check.
+                 */
                 smp_mb(); /* explicit MB (B) */
         }
 }
 
 /*
  * Drop a reference to the resource addressed by a key.
- * The hash bucket spinlock must not be held.
+ * The hash bucket spinlock must not be held. This is
+ * a no-op for private futexes, see comment in the get
+ * counterpart.
  */
 static void drop_futex_key_refs(union futex_key *key)
 {