// SPDX-License-Identifier: GPL-2.0-only
/*
 * Complete definition from Linux v6.18 mm/filemap.c.
 * Source: https://github.com/torvalds/linux/blob/v6.18/mm/filemap.c
 * Copyright (C) 1994-1999  Linus Torvalds
 * Kernel excerpt; not a standalone user-space program.
 * The book's exact source tag is not asserted.
 */

static void folio_wake_bit(struct folio *folio, int bit_nr)
{
	wait_queue_head_t *q = folio_waitqueue(folio);
	struct wait_page_key key;
	unsigned long flags;

	key.folio = folio;
	key.bit_nr = bit_nr;
	key.page_match = 0;

	spin_lock_irqsave(&q->lock, flags);
	__wake_up_locked_key(q, TASK_NORMAL, &key);

	/*
	 * It's possible to miss clearing waiters here, when we woke our page
	 * waiters, but the hashed waitqueue has waiters for other pages on it.
	 * That's okay, it's a rare case. The next waker will clear it.
	 *
	 * Note that, depending on the page pool (buddy, hugetlb, ZONE_DEVICE,
	 * other), the flag may be cleared in the course of freeing the page;
	 * but that is not required for correctness.
	 */
	if (!waitqueue_active(q) || !key.page_match)
		folio_clear_waiters(folio);

	spin_unlock_irqrestore(&q->lock, flags);
}