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Subject[PATCH V3] futex: add futex_q static initializer
Date
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@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@elte.hu>
CC: Eric Dumazet <eric.dumazet@gmail.com>
CC: John Kacur <jkacur@redhat.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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