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authorDarren Hart <dvhltc@us.ibm.com>2008-12-17 17:29:56 -0800
committerIngo Molnar <mingo@elte.hu>2008-12-18 11:42:23 +0100
commit73500ac545d24610eb2cf8579ffc88957e9c5847 (patch)
tree1e36cc5585bd25a1d8cbe973d229250bee0cef32
parent1acdac104668a0834cfa267de9946fac7764d486 (diff)
futex: rename field in futex_q to clarify single waiter semantics
Impact: simplify code I've tripped over the naming of this field a couple times. The futex_q uses a "waiters" list to represent a single blocked task and then calles wake_up_all(). This can lead to confusion in trying to understand the intent of the code, which is to have a single futex_q for every task waiting on a futex. This patch corrects the problem, using a single pointer to the waiting task, and an appropriate call to wake_up, rather than wake_up_all. Compile and boot tested on an 8way x86_64 machine. Signed-off-by: Darren Hart <dvhltc@us.ibm.com> Acked-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Ingo Molnar <mingo@elte.hu>
-rw-r--r--kernel/futex.c11
1 files changed, 6 insertions, 5 deletions
diff --git a/kernel/futex.c b/kernel/futex.c
index ba0d3b83c091..99f8acce08bf 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -92,11 +92,12 @@ struct futex_pi_state {
* A futex_q has a woken state, just like tasks have TASK_RUNNING.
* It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
* The order of wakup is always to make the first condition true, then
- * wake up q->waiters, then make the second condition true.
+ * wake up q->waiter, then make the second condition true.
*/
struct futex_q {
struct plist_node list;
- wait_queue_head_t waiters;
+ /* There can only be a single waiter */
+ wait_queue_head_t waiter;
/* Which hash list lock to use: */
spinlock_t *lock_ptr;
@@ -573,7 +574,7 @@ static void wake_futex(struct futex_q *q)
* The lock in wake_up_all() is a crucial memory barrier after the
* plist_del() and also before assigning to q->lock_ptr.
*/
- wake_up_all(&q->waiters);
+ wake_up(&q->waiter);
/*
* The waiting task can free the futex_q as soon as this is written,
* without taking any locks. This must come last.
@@ -930,7 +931,7 @@ static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
{
struct futex_hash_bucket *hb;
- init_waitqueue_head(&q->waiters);
+ init_waitqueue_head(&q->waiter);
get_futex_key_refs(&q->key);
hb = hash_futex(&q->key);
@@ -1221,7 +1222,7 @@ static int futex_wait(u32 __user *uaddr, int fshared,
/* add_wait_queue is the barrier after __set_current_state. */
__set_current_state(TASK_INTERRUPTIBLE);
- add_wait_queue(&q.waiters, &wait);
+ add_wait_queue(&q.waiter, &wait);
/*
* !plist_node_empty() is safe here without any lock.
* q.lock_ptr != 0 is not safe, because of ordering against wakeup.