[PATCH 2/6] mm: migrate: Lock buffers before migrate_page_move_mapping()

Jan Kara
2018-12-11T17:21:51Z

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().

Signed-off-by: Jan Kara <jack@suse.cz>
---
mm/migrate.c | 39 +++++++++++++--------------------------
1 file changed, 13 insertions(+), 26 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 789c7bc90a0c..d58a8ecf275e 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -490,20 +490,6 @@ 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.
@@ -779,24 +765,23 @@ 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));
@@ -818,6 +803,8 @@ 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);
@@ -826,7 +813,7 @@ int buffer_migrate_page(struct address_space *mapping,

} while (bh != head);

- return MIGRATEPAGE_SUCCESS;
+ return rc;
}
EXPORT_SYMBOL(buffer_migrate_page);
#endif
--
2.16.4