Re: wait_on_page_bit_common(TASK_KILLABLE, EXCLUSIVE) can miss wakeup?

[Oleg Nesterov <oleg@redhat.com>]

On 06/30, Oleg Nesterov wrote:
>
> may be someting like this

or this ...

	for (;;) {
		int intr = 0;

		spin_lock_irq(&q->lock);
		if (signal_pending_state(state, current)) {
			/* see the comment in prepare_to_wait_event() */
			list_del_init(&wait->entry);
			intr = 1;
		} else {
			if (likely(list_empty(&wait->entry))) {
				__add_wait_queue_entry_tail(q, wait);
				SetPageWaiters(page);
			}
			set_current_state(state);
		}
		spin_unlock_irq(&q->lock);

		bit_is_set = test_bit(bit_nr, &page->flags);
		if (behavior == DROP)
			put_page(page);

		if (!bit_is_set) {
			if (behavior != EXCLUSIVE)
				break;
			if (!test_and_set_bit_lock(bit_nr, &page->flags))
				break;
		}

		if (intr) {
			ret = -EINTR;
			break;
		}

		io_schedule();

		if (behavior == DROP) {
			/*
			 * We can no longer safely access page->flags:
			 * even if CONFIG_MEMORY_HOTREMOVE is not enabled,
			 * there is a risk of waiting forever on a page reused
			 * for something that keeps it locked indefinitely.
			 * But best check for -EINTR before breaking.
			 */
			if (signal_pending_state(state, current))
				ret = -EINTR;
			break;
		}
	}

Oleg.