Merge branch 'locking-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

{

	struct rwsem_waiter *waiter, *tmp;

	long oldcount, woken = 0, adjustment = 0;

	struct list_head wlist;

	/*

	 * Take a peek at the queue head waiter such that we can determine

	 * 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.

	 *

	 * We have to do wakeup in 2 passes to prevent the possibility that

	 * the reader count may be decremented before it is incremented. It

	 * is because the to-be-woken waiter may not have slept yet. So it

	 * may see waiter->task got cleared, finish its critical section and

	 * do an unlock before the reader count increment.

	 *

	 * 1) Collect the read-waiters in a separate list, count them and

	 *    fully increment the reader count in rwsem.

	 * 2) For each waiters in the new list, clear waiter->task and

	 *    put them into wake_q to be woken up later.

	 */

	list_for_each_entry_safe(waiter, tmp, &sem->wait_list, list) {

		struct task_struct *tsk;

	list_for_each_entry(waiter, &sem->wait_list, list) {

		if (waiter->type == RWSEM_WAITING_FOR_WRITE)

			break;

		woken++;

		tsk = waiter->task;

	}

	list_cut_before(&wlist, &sem->wait_list, &waiter->list);

	adjustment = woken * RWSEM_ACTIVE_READ_BIAS - adjustment;

	lockevent_cond_inc(rwsem_wake_reader, woken);

	if (list_empty(&sem->wait_list)) {

		/* hit end of list above */

		adjustment -= RWSEM_WAITING_BIAS;

	}

	if (adjustment)

		atomic_long_add(adjustment, &sem->count);

	/* 2nd pass */

	list_for_each_entry_safe(waiter, tmp, &wlist, list) {

		struct task_struct *tsk;

		tsk = waiter->task;

		get_task_struct(tsk);

		list_del(&waiter->list);

		/*

		 * Ensure calling get_task_struct() before setting the reader

		 * waiter to nil such that rwsem_down_read_failed() cannot

		 */

		wake_q_add_safe(wake_q, tsk);

	}

	adjustment = woken * RWSEM_ACTIVE_READ_BIAS - adjustment;

	lockevent_cond_inc(rwsem_wake_reader, woken);

	if (list_empty(&sem->wait_list)) {

		/* hit end of list above */

		adjustment -= RWSEM_WAITING_BIAS;

	}

	if (adjustment)

		atomic_long_add(adjustment, &sem->count);

}

/*