// SPDX-License-Identifier: GPL-2.0
/*
 *  linux/mm/page_io.c
 *
 *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
 *
 *  Swap reorganised 29.12.95, 
 *  Asynchronous swapping added 30.12.95. Stephen Tweedie
 *  Removed race in async swapping. 14.4.1996. Bruno Haible
 *  Add swap of shared pages through the page cache. 20.2.1998. Stephen Tweedie
 *  Always use brw_page, life becomes simpler. 12 May 1998 Eric Biederman
 */

/*
 * Official Linux v6.0: mm/page_io.c
 * https://github.com/torvalds/linux/blob/v6.0/mm/page_io.c#L448
 * Exact definition/declaration; not a reconstruction of a book listing.
 * See GPL-2.0.txt. Not a standalone translation unit.
 */

int swap_readpage(struct page *page, bool synchronous,
		  struct swap_iocb **plug)
{
	struct bio *bio;
	int ret = 0;
	struct swap_info_struct *sis = page_swap_info(page);
	bool workingset = PageWorkingset(page);
	unsigned long pflags;

	VM_BUG_ON_PAGE(!PageSwapCache(page) && !synchronous, page);
	VM_BUG_ON_PAGE(!PageLocked(page), page);
	VM_BUG_ON_PAGE(PageUptodate(page), page);

	/*
	 * Count submission time as memory stall. When the device is congested,
	 * or the submitting cgroup IO-throttled, submission can be a
	 * significant part of overall IO time.
	 */
	if (workingset)
		psi_memstall_enter(&pflags);
	delayacct_swapin_start();

	if (frontswap_load(page) == 0) {
		SetPageUptodate(page);
		unlock_page(page);
		goto out;
	}

	if (data_race(sis->flags & SWP_FS_OPS)) {
		swap_readpage_fs(page, plug);
		goto out;
	}

	if (sis->flags & SWP_SYNCHRONOUS_IO) {
		ret = bdev_read_page(sis->bdev, swap_page_sector(page), page);
		if (!ret) {
			count_vm_event(PSWPIN);
			goto out;
		}
	}

	ret = 0;
	bio = bio_alloc(sis->bdev, 1, REQ_OP_READ, GFP_KERNEL);
	bio->bi_iter.bi_sector = swap_page_sector(page);
	bio->bi_end_io = end_swap_bio_read;
	bio_add_page(bio, page, thp_size(page), 0);
	/*
	 * Keep this task valid during swap readpage because the oom killer may
	 * attempt to access it in the page fault retry time check.
	 */
	if (synchronous) {
		get_task_struct(current);
		bio->bi_private = current;
	}
	count_vm_event(PSWPIN);
	bio_get(bio);
	submit_bio(bio);
	while (synchronous) {
		set_current_state(TASK_UNINTERRUPTIBLE);
		if (!READ_ONCE(bio->bi_private))
			break;

		blk_io_schedule();
	}
	__set_current_state(TASK_RUNNING);
	bio_put(bio);

out:
	if (workingset)
		psi_memstall_leave(&pflags);
	delayacct_swapin_end();
	return ret;
}