linux-kernel - [PATCH V3] futex: add futex

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Date:	Mon,  8 Nov 2010 13:40:28 -0800
From:	Darren Hart <dvhart@...ux.intel.com>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:	Darren Hart <dvhart@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Eric Dumazet <eric.dumazet@...il.com>,
	John Kacur <jkacur@...hat.com>
Subject: [PATCH V3] 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 <dvhart@...ux.intel.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...e.hu>
CC: Eric Dumazet <eric.dumazet@...il.com>
CC: John Kacur <jkacur@...hat.com>
---
 kernel/futex.c |   25 ++++++++++---------------
 1 files changed, 10 insertions(+), 15 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index fd3fbe1..e6df2de 100644
--- a/kernel/futex.c
+++ b/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
@@ -1751,7 +1757,6 @@ 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;
@@ -1792,16 +1797,12 @@ 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;
@@ -1892,7 +1893,7 @@ 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())
@@ -1906,11 +1907,7 @@ 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;
@@ -2198,8 +2195,8 @@ 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)
@@ -2222,12 +2219,10 @@ 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;
-- 
1.7.1

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