futex: Add futex_q static initializer

The futex_q struct has grown considerably over the last couple years. I
believe it now merits a static initializer to avoid uninitialized data
errors (having spent more time than I care to admit debugging an uninitialized
q.bitset in an experimental new op code).

With the key initializer built in, several of the FUTEX_KEY_INIT calls can
be removed.

V2: use a static variable instead of an init macro.
    use a C99 initializer and don't rely on variable ordering in the struct.
V3: make futex_q_init const

Signed-off-by: Darren Hart <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Eric Dumazet <[email protected]>
Cc: John Kacur <[email protected]>
Cc: Ingo Molnar <[email protected]>
LKML-Reference: <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>

kernel/futex.c

@@ -131,6 +131,12 @@ struct futex_q {
 	u32 bitset;
 };
 
+static const struct futex_q futex_q_init = {
+	/* list gets initialized in queue_me()*/
+	.key = FUTEX_KEY_INIT,
+	.bitset = FUTEX_BITSET_MATCH_ANY
+};
+
 /*
  * Hash buckets are shared by all the futex_keys that hash to the same
  * location.  Each key may have multiple futex_q structures, one for each task
@@ -1750,7 +1756,6 @@ static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
 	 * rare, but normal.
 	 */
 retry:
-	q->key = FUTEX_KEY_INIT;
 	ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key);
 	if (unlikely(ret != 0))
 		return ret;
@@ -1791,16 +1796,12 @@ static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
 	struct hrtimer_sleeper timeout, *to = NULL;
 	struct restart_block *restart;
 	struct futex_hash_bucket *hb;
-	struct futex_q q;
+	struct futex_q q = futex_q_init;
 	int ret;
 
 	if (!bitset)
 		return -EINVAL;
-
-	q.pi_state = NULL;
 	q.bitset = bitset;
-	q.rt_waiter = NULL;
-	q.requeue_pi_key = NULL;
 
 	if (abs_time) {
 		to = &timeout;
@@ -1891,7 +1892,7 @@ static int futex_lock_pi(u32 __user *uaddr, unsigned int flags, int detect,
 {
 	struct hrtimer_sleeper timeout, *to = NULL;
 	struct futex_hash_bucket *hb;
-	struct futex_q q;
+	struct futex_q q = futex_q_init;
 	int res, ret;
 
 	if (refill_pi_state_cache())
@@ -1905,11 +1906,7 @@ static int futex_lock_pi(u32 __user *uaddr, unsigned int flags, int detect,
 		hrtimer_set_expires(&to->timer, *time);
 	}
 
-	q.pi_state = NULL;
-	q.rt_waiter = NULL;
-	q.requeue_pi_key = NULL;
 retry:
-	q.key = FUTEX_KEY_INIT;
 	ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key);
 	if (unlikely(ret != 0))
 		goto out;
@@ -2197,8 +2194,8 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
 	struct rt_mutex_waiter rt_waiter;
 	struct rt_mutex *pi_mutex = NULL;
 	struct futex_hash_bucket *hb;
-	union futex_key key2;
-	struct futex_q q;
+	union futex_key key2 = FUTEX_KEY_INIT;
+	struct futex_q q = futex_q_init;
 	int res, ret;
 
 	if (!bitset)
@@ -2221,12 +2218,10 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
 	debug_rt_mutex_init_waiter(&rt_waiter);
 	rt_waiter.task = NULL;
 
-	key2 = FUTEX_KEY_INIT;
 	ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2);
 	if (unlikely(ret != 0))
 		goto out;
 
-	q.pi_state = NULL;
 	q.bitset = bitset;
 	q.rt_waiter = &rt_waiter;
 	q.requeue_pi_key = &key2;