1 files changed, 17 insertions, 16 deletions

diff --git a/kernel/futex.c b/kernel/futex.c
index 2579e407ff67..f9984c363e9a 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1090,9 +1090,11 @@ static void __unqueue_futex(struct futex_q *q)
 
 /*
  * The hash bucket lock must be held when this is called.
- * Afterwards, the futex_q must not be accessed.
+ * Afterwards, the futex_q must not be accessed. Callers
+ * must ensure to later call wake_up_q() for the actual
+ * wakeups to occur.
  */
-static void wake_futex(struct futex_q *q)
+static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q)
 {
         struct task_struct *p = q->task;
 
@@ -1100,14 +1102,10 @@ static void wake_futex(struct futex_q *q)
                 return;
 
         /*
-         * We set q->lock_ptr = NULL _before_ we wake up the task. If
-         * a non-futex wake up happens on another CPU then the task
-         * might exit and p would dereference a non-existing task
-         * struct. Prevent this by holding a reference on p across the
-         * wake up.
+         * Queue the task for later wakeup for after we've released
+         * the hb->lock. wake_q_add() grabs reference to p.
          */
-        get_task_struct(p);
-
+        wake_q_add(wake_q, p);
         __unqueue_futex(q);
         /*
          * The waiting task can free the futex_q as soon as
@@ -1117,9 +1115,6 @@ static void wake_futex(struct futex_q *q)
          */
         smp_wmb();
         q->lock_ptr = NULL;
-
-        wake_up_state(p, TASK_NORMAL);
-        put_task_struct(p);
 }
 
 static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)
@@ -1217,6 +1212,7 @@ futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
         struct futex_q *this, *next;
         union futex_key key = FUTEX_KEY_INIT;
         int ret;
+        WAKE_Q(wake_q);
 
         if (!bitset)
                 return -EINVAL;
@@ -1244,13 +1240,14 @@ futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
                         if (!(this->bitset & bitset))
                                 continue;
 
-                        wake_futex(this);
+                        mark_wake_futex(&wake_q, this);
                         if (++ret >= nr_wake)
                                 break;
                 }
         }
 
         spin_unlock(&hb->lock);
+        wake_up_q(&wake_q);
 out_put_key:
         put_futex_key(&key);
 out:
@@ -1269,6 +1266,7 @@ futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
         struct futex_hash_bucket *hb1, *hb2;
         struct futex_q *this, *next;
         int ret, op_ret;
+        WAKE_Q(wake_q);
 
 retry:
         ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, VERIFY_READ);
@@ -1320,7 +1318,7 @@ retry_private:
                                 ret = -EINVAL;
                                 goto out_unlock;
                         }
-                        wake_futex(this);
+                        mark_wake_futex(&wake_q, this);
                         if (++ret >= nr_wake)
                                 break;
                 }
@@ -1334,7 +1332,7 @@ retry_private:
                                         ret = -EINVAL;
                                         goto out_unlock;
                                 }
-                                wake_futex(this);
+                                mark_wake_futex(&wake_q, this);
                                 if (++op_ret >= nr_wake2)
                                         break;
                         }
@@ -1344,6 +1342,7 @@ retry_private:
 
 out_unlock:
         double_unlock_hb(hb1, hb2);
+        wake_up_q(&wake_q);
 out_put_keys:
         put_futex_key(&key2);
 out_put_key1:
@@ -1503,6 +1502,7 @@ static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
         struct futex_pi_state *pi_state = NULL;
         struct futex_hash_bucket *hb1, *hb2;
         struct futex_q *this, *next;
+        WAKE_Q(wake_q);
 
         if (requeue_pi) {
                 /*
@@ -1679,7 +1679,7 @@ retry_private:
                  * woken by futex_unlock_pi().
                  */
                 if (++task_count <= nr_wake && !requeue_pi) {
-                        wake_futex(this);
+                        mark_wake_futex(&wake_q, this);
                         continue;
                 }
 
@@ -1719,6 +1719,7 @@ retry_private:
 out_unlock:
         free_pi_state(pi_state);
         double_unlock_hb(hb1, hb2);
+        wake_up_q(&wake_q);
         hb_waiters_dec(hb2);
 
         /*