ubifs: wait for page writeback to provide stable pages

When stable pages are required, we have to wait if the page is just
going to disk and we want to modify it.  Add proper callback to
ubifs_vm_page_mkwrite().

Signed-off-by: Jan Kara <[email protected]>
Signed-off-by: Darrick J. Wong <[email protected]>
Cc: Artem Bityutskiy <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Joel Becker <[email protected]>
Cc: Mark Fasheh <[email protected]>
Cc: Steven Whitehouse <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Eric Van Hensbergen <[email protected]>
Cc: Ron Minnich <[email protected]>
Cc: Latchesar Ionkov <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: jankara

fs/ubifs/file.c

@@ -1522,6 +1522,7 @@ static int ubifs_vm_page_mkwrite(struct vm_area_struct *vma,
 			ubifs_release_dirty_inode_budget(c, ui);
 	}
 
+	wait_for_stable_page(page);
 	unlock_page(page);
 	return 0;