From: Jan Kara <jack@xxxxxxx> Subject: 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@xxxxxxx Signed-off-by: Jan Kara <jack@xxxxxxx> Acked-by: Mel Gorman <mgorman@xxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- --- a/mm/migrate.c~mm-migrate-lock-buffers-before-migrate_page_move_mapping +++ a/mm/migrate.c @@ -487,20 +487,6 @@ int migrate_page_move_mapping(struct add } /* - * 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_s { 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_s 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_s } while (bh != head); - return MIGRATEPAGE_SUCCESS; + return rc; } EXPORT_SYMBOL(buffer_migrate_page); #endif _
