* - woken process blocks are discarded from the list after having task zeroed
* - writers are only marked woken if downgrading is false
*/
-static struct rw_semaphore *
-__rwsem_mark_wake(struct rw_semaphore *sem,
- enum rwsem_wake_type wake_type, struct wake_q_head *wake_q)
+static void __rwsem_mark_wake(struct rw_semaphore *sem,
+ enum rwsem_wake_type wake_type,
+ struct wake_q_head *wake_q)
{
- struct rwsem_waiter *waiter;
- struct task_struct *tsk;
- struct list_head *next;
- long oldcount, woken, loop, adjustment;
+ struct rwsem_waiter *waiter, *tmp;
+ long oldcount, woken = 0, adjustment = 0;
+
+ /*
+ * Take a peek at the queue head waiter such that we can determine
+ * the wakeup(s) to perform.
+ */
+ waiter = list_first_entry(&sem->wait_list, struct rwsem_waiter, list);
- waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
if (waiter->type == RWSEM_WAITING_FOR_WRITE) {
if (wake_type == RWSEM_WAKE_ANY) {
/*
*/
wake_q_add(wake_q, waiter->task);
}
- goto out;
+
+ return;
}
- /* Writers might steal the lock before we grant it to the next reader.
+ /*
+ * Writers might steal the lock before we grant it to the next reader.
* We prefer to do the first reader grant before counting readers
* so we can bail out early if a writer stole the lock.
*/
- adjustment = 0;
if (wake_type != RWSEM_WAKE_READ_OWNED) {
adjustment = RWSEM_ACTIVE_READ_BIAS;
try_reader_grant:
oldcount = atomic_long_fetch_add(adjustment, &sem->count);
-
if (unlikely(oldcount < RWSEM_WAITING_BIAS)) {
/*
* If the count is still less than RWSEM_WAITING_BIAS
*/
if (atomic_long_add_return(-adjustment, &sem->count) <
RWSEM_WAITING_BIAS)
- goto out;
+ return;
+
/* Last active locker left. Retry waking readers. */
goto try_reader_grant;
}
rwsem_set_reader_owned(sem);
}
- /* Grant an infinite number of read locks to the readers at the front
- * of the queue. Note we increment the 'active part' of the count by
- * the number of readers before waking any processes up.
+ /*
+ * Grant an infinite number of read locks to the readers at the front
+ * of the queue. We know that woken will be at least 1 as we accounted
+ * for above. Note we increment the 'active part' of the count by the
+ * number of readers before waking any processes up.
*/
- woken = 0;
- do {
- woken++;
+ list_for_each_entry_safe(waiter, tmp, &sem->wait_list, list) {
+ struct task_struct *tsk;
- if (waiter->list.next == &sem->wait_list)
+ if (waiter->type == RWSEM_WAITING_FOR_WRITE)
break;
- waiter = list_entry(waiter->list.next,
- struct rwsem_waiter, list);
-
- } while (waiter->type != RWSEM_WAITING_FOR_WRITE);
-
- adjustment = woken * RWSEM_ACTIVE_READ_BIAS - adjustment;
- if (waiter->type != RWSEM_WAITING_FOR_WRITE)
- /* hit end of list above */
- adjustment -= RWSEM_WAITING_BIAS;
-
- if (adjustment)
- atomic_long_add(adjustment, &sem->count);
-
- next = sem->wait_list.next;
- loop = woken;
- do {
- waiter = list_entry(next, struct rwsem_waiter, list);
- next = waiter->list.next;
+ woken++;
tsk = waiter->task;
wake_q_add(wake_q, tsk);
+ list_del(&waiter->list);
/*
* Ensure that the last operation is setting the reader
* waiter to nil such that rwsem_down_read_failed() cannot
* to the task to wakeup.
*/
smp_store_release(&waiter->task, NULL);
- } while (--loop);
+ }
- sem->wait_list.next = next;
- next->prev = &sem->wait_list;
+ adjustment = woken * RWSEM_ACTIVE_READ_BIAS - adjustment;
+ if (list_empty(&sem->wait_list)) {
+ /* hit end of list above */
+ adjustment -= RWSEM_WAITING_BIAS;
+ }
- out:
- return sem;
+ if (adjustment)
+ atomic_long_add(adjustment, &sem->count);
}
/*
struct task_struct *tsk = current;
WAKE_Q(wake_q);
- /* set up my own style of waitqueue */
waiter.task = tsk;
waiter.type = RWSEM_WAITING_FOR_READ;
/* we're now waiting on the lock, but no longer actively locking */
count = atomic_long_add_return(adjustment, &sem->count);
- /* If there are no active locks, wake the front queued process(es).
+ /*
+ * If there are no active locks, wake the front queued process(es).
*
* If there are no writers and we are first in the queue,
* wake our own waiter to join the existing active readers !
if (count == RWSEM_WAITING_BIAS ||
(count > RWSEM_WAITING_BIAS &&
adjustment != -RWSEM_ACTIVE_READ_BIAS))
- sem = __rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
+ __rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
raw_spin_unlock_irq(&sem->wait_lock);
wake_up_q(&wake_q);
if (count > RWSEM_WAITING_BIAS) {
WAKE_Q(wake_q);
- sem = __rwsem_mark_wake(sem, RWSEM_WAKE_READERS, &wake_q);
+ __rwsem_mark_wake(sem, RWSEM_WAKE_READERS, &wake_q);
/*
* The wakeup is normally called _after_ the wait_lock
* is released, but given that we are proactively waking
raw_spin_lock_irqsave(&sem->wait_lock, flags);
locked:
- /* do nothing if list empty */
if (!list_empty(&sem->wait_list))
- sem = __rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
+ __rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);
raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
wake_up_q(&wake_q);
raw_spin_lock_irqsave(&sem->wait_lock, flags);
- /* do nothing if list empty */
if (!list_empty(&sem->wait_list))
- sem = __rwsem_mark_wake(sem, RWSEM_WAKE_READ_OWNED, &wake_q);
+ __rwsem_mark_wake(sem, RWSEM_WAKE_READ_OWNED, &wake_q);
raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
wake_up_q(&wake_q);
projects / cascardo / linux.git / blobdiff