[3.11.y.z,extended,stable] Patch "futex: Add another early deadlock detection check" has been added to staging queue

diff --git a/kernel/futex.c b/kernel/futex.c
index 15a7d724e6b2..3e876641f4af 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -595,7 +595,8 @@  void exit_pi_state_list(struct task_struct *curr)

 static int
 lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
-		union futex_key *key, struct futex_pi_state **ps)
+		union futex_key *key, struct futex_pi_state **ps,
+		struct task_struct *task)
 {
 	struct futex_pi_state *pi_state = NULL;
 	struct futex_q *this, *next;
@@ -639,6 +640,16 @@  lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
 					return -EINVAL;
 			}

+			/*
+			 * Protect against a corrupted uval. If uval
+			 * is 0x80000000 then pid is 0 and the waiter
+			 * bit is set. So the deadlock check in the
+			 * calling code has failed and we did not fall
+			 * into the check above due to !pid.
+			 */
+			if (task && pi_state->owner == task)
+				return -EDEADLK;
+
 			atomic_inc(&pi_state->refcount);
 			*ps = pi_state;

@@ -788,7 +799,7 @@  retry:
 	 * We dont have the lock. Look up the PI state (or create it if
 	 * we are the first waiter):
 	 */
-	ret = lookup_pi_state(uval, hb, key, ps);
+	ret = lookup_pi_state(uval, hb, key, ps, task);

 	if (unlikely(ret)) {
 		switch (ret) {
@@ -1198,7 +1209,7 @@  void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
  *
  * Return:
  *  0 - failed to acquire the lock atomically;
- *  1 - acquired the lock;
+ * >0 - acquired the lock, return value is vpid of the top_waiter
  * <0 - error
  */
 static int futex_proxy_trylock_atomic(u32 __user *pifutex,
@@ -1209,7 +1220,7 @@  static int futex_proxy_trylock_atomic(u32 __user *pifutex,
 {
 	struct futex_q *top_waiter = NULL;
 	u32 curval;
-	int ret;
+	int ret, vpid;

 	if (get_futex_value_locked(&curval, pifutex))
 		return -EFAULT;
@@ -1237,11 +1248,13 @@  static int futex_proxy_trylock_atomic(u32 __user *pifutex,
 	 * the contended case or if set_waiters is 1.  The pi_state is returned
 	 * in ps in contended cases.
 	 */
+	vpid = task_pid_vnr(top_waiter->task);
 	ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
 				   set_waiters);
-	if (ret == 1)
+	if (ret == 1) {
 		requeue_pi_wake_futex(top_waiter, key2, hb2);
-
+		return vpid;
+	}
 	return ret;
 }

@@ -1273,7 +1286,6 @@  static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
 	struct futex_hash_bucket *hb1, *hb2;
 	struct plist_head *head1;
 	struct futex_q *this, *next;
-	u32 curval2;

 	if (requeue_pi) {
 		/*
@@ -1359,16 +1371,25 @@  retry_private:
 		 * At this point the top_waiter has either taken uaddr2 or is
 		 * waiting on it.  If the former, then the pi_state will not
 		 * exist yet, look it up one more time to ensure we have a
-		 * reference to it.
+		 * reference to it. If the lock was taken, ret contains the
+		 * vpid of the top waiter task.
 		 */
-		if (ret == 1) {
+		if (ret > 0) {
 			WARN_ON(pi_state);
 			drop_count++;
 			task_count++;
-			ret = get_futex_value_locked(&curval2, uaddr2);
-			if (!ret)
-				ret = lookup_pi_state(curval2, hb2, &key2,
-						      &pi_state);
+			/*
+			 * If we acquired the lock, then the user
+			 * space value of uaddr2 should be vpid. It
+			 * cannot be changed by the top waiter as it
+			 * is blocked on hb2 lock if it tries to do
+			 * so. If something fiddled with it behind our
+			 * back the pi state lookup might unearth
+			 * it. So we rather use the known value than
+			 * rereading and handing potential crap to
+			 * lookup_pi_state.
+			 */
+			ret = lookup_pi_state(ret, hb2, &key2, &pi_state, NULL);
 		}

 		switch (ret) {