Merge tag 'imx-fixes-3.18-2' of git://git.kernel.org/pub/scm/linux/kernel/git/shawngu...

[cascardo/linux.git] / kernel / futex.c

diff --git a/kernel/futex.c b/kernel/futex.c
index 815d7af..63678b5 100644 (file)
--- 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):
  *
@@ -343,12 +342,21 @@ static void get_futex_key_refs(union futex_key *key)
        case FUT_OFF_MMSHARED:
                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)
 {
@@ -639,8 +647,14 @@ static struct futex_pi_state * alloc_pi_state(void)
        return pi_state;
 }
 
+/*
+ * Must be called with the hb lock held.
+ */
 static void free_pi_state(struct futex_pi_state *pi_state)
 {
+       if (!pi_state)
+               return;
+
        if (!atomic_dec_and_test(&pi_state->refcount))
                return;
 
@@ -1519,15 +1533,6 @@ static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
        }
 
 retry:
-       if (pi_state != NULL) {
-               /*
-                * We will have to lookup the pi_state again, so free this one
-                * to keep the accounting correct.
-                */
-               free_pi_state(pi_state);
-               pi_state = NULL;
-       }
-
        ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
        if (unlikely(ret != 0))
                goto out;
@@ -1617,6 +1622,8 @@ retry_private:
                case 0:
                        break;
                case -EFAULT:
+                       free_pi_state(pi_state);
+                       pi_state = NULL;
                        double_unlock_hb(hb1, hb2);
                        hb_waiters_dec(hb2);
                        put_futex_key(&key2);
@@ -1632,6 +1639,8 @@ retry_private:
                         *   exit to complete.
                         * - The user space value changed.
                         */
+                       free_pi_state(pi_state);
+                       pi_state = NULL;
                        double_unlock_hb(hb1, hb2);
                        hb_waiters_dec(hb2);
                        put_futex_key(&key2);
@@ -1708,6 +1717,7 @@ retry_private:
        }
 
 out_unlock:
+       free_pi_state(pi_state);
        double_unlock_hb(hb1, hb2);
        hb_waiters_dec(hb2);
 
@@ -1725,8 +1735,6 @@ out_put_keys:
 out_put_key1:
        put_futex_key(&key1);
 out:
-       if (pi_state != NULL)
-               free_pi_state(pi_state);
        return ret ? ret : task_count;
 }