[PATCH] lockdep: annotate sb ->s_umount

The s_umount rwsem needs to be classified as per-superblock since it's
perfectly legit to keep multiple of those recursively in the VFS locking
rules.

Has no effect on non-lockdep kernels.
Signed-off-by: NArjan van de Ven <arjan@linux.intel.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

fs/super.c

@@ -72,6 +72,7 @@ static struct super_block *alloc_super(struct file_system_type *type)
 		INIT_LIST_HEAD(&s->s_inodes);
 		init_rwsem(&s->s_umount);
 		mutex_init(&s->s_lock);
+		lockdep_set_class(&s->s_umount, &type->s_umount_key);
 		/*
 		 * The locking rules for s_lock are up to the
 		 * filesystem. For example ext3fs has different

include/linux/fs.h

@@ -1296,6 +1296,7 @@ struct file_system_type {
 	struct file_system_type * next;
 	struct list_head fs_supers;
 	struct lock_class_key s_lock_key;
+	struct lock_class_key s_umount_key;
 };
 
 extern int get_sb_bdev(struct file_system_type *fs_type,