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Commit cc4f11e6 authored by Jan Kara's avatar Jan Kara Committed by Linus Torvalds
Browse files

mm: migrate: lock buffers before migrate_page_move_mapping() 

Lock buffers before calling into migrate_page_move_mapping() so that that
function doesn't have to know about buffers (which is somewhat unexpected
anyway) and all the buffer head logic is in buffer_migrate_page().

Link: http://lkml.kernel.org/r/20181211172143.7358-3-jack@suse.cz


Signed-off-by: default avatarJan Kara <jack@suse.cz>
Acked-by: default avatarMel Gorman <mgorman@suse.de>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 0b3901b3

mm/migrate.c

+13 −26
Original line number Diff line number Diff line
@@ -486,20 +486,6 @@ int migrate_page_move_mapping(struct address_space *mapping, 
		return -EAGAIN;

	}



	/*

	 * In the async migration case of moving a page with buffers, lock the

	 * buffers using trylock before the mapping is moved. If the mapping

	 * was moved, we later failed to lock the buffers and could not move

	 * the mapping back due to an elevated page count, we would have to

	 * block waiting on other references to be dropped.

	 */

	if (mode == MIGRATE_ASYNC && head &&

			!buffer_migrate_lock_buffers(head, mode)) {

		page_ref_unfreeze(page, expected_count);

		xas_unlock_irq(&xas);

		return -EAGAIN;

	}



	/*

	 * Now we know that no one else is looking at the page:

	 * no turning back from here.
@@ -775,24 +761,23 @@ int buffer_migrate_page(struct address_space *mapping, 
{

	struct buffer_head *bh, *head;

	int rc;

	int expected_count;



	if (!page_has_buffers(page))

		return migrate_page(mapping, newpage, page, mode);



	head = page_buffers(page);

	/* Check whether page does not have extra refs before we do more work */

	expected_count = expected_page_refs(page);

	if (page_count(page) != expected_count)

		return -EAGAIN;



	rc = migrate_page_move_mapping(mapping, newpage, page, head, mode, 0);

	head = page_buffers(page);

	if (!buffer_migrate_lock_buffers(head, mode))

		return -EAGAIN;



	rc = migrate_page_move_mapping(mapping, newpage, page, NULL, mode, 0);

	if (rc != MIGRATEPAGE_SUCCESS)

		return rc;



	/*

	 * In the async case, migrate_page_move_mapping locked the buffers

	 * with an IRQ-safe spinlock held. In the sync case, the buffers

	 * need to be locked now

	 */

	if (mode != MIGRATE_ASYNC)

		BUG_ON(!buffer_migrate_lock_buffers(head, mode));

		goto unlock_buffers;



	ClearPagePrivate(page);

	set_page_private(newpage, page_private(page));
@@ -814,6 +799,8 @@ int buffer_migrate_page(struct address_space *mapping, 
	else

		migrate_page_states(newpage, page);



	rc = MIGRATEPAGE_SUCCESS;

unlock_buffers:

	bh = head;

	do {

		unlock_buffer(bh);
@@ -822,7 +809,7 @@ int buffer_migrate_page(struct address_space *mapping, 


	} while (bh != head);



	return MIGRATEPAGE_SUCCESS;

	return rc;

}

EXPORT_SYMBOL(buffer_migrate_page);

#endif