fs: simplify setup_bdev_super() calls

There's no need to drop s_umount anymore now that we removed all sources
where s_umount is taken beneath open_mutex or bd_holder_lock.

Link: https://lore.kernel.org/r/20231024-vfs-super-rework-v1-1-37a8aa697148@kernel.orgReviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>

fs/super.c

@@ -1601,15 +1601,7 @@ int get_tree_bdev(struct fs_context *fc,
 			return -EBUSY;
 		}
 	} else {
-		/*
-		 * We drop s_umount here because we need to open the bdev and
-		 * bdev->open_mutex ranks above s_umount (blkdev_put() ->
-		 * bdev_mark_dead()). It is safe because we have active sb
-		 * reference and SB_BORN is not set yet.
-		 */
-		super_unlock_excl(s);
 		error = setup_bdev_super(s, fc->sb_flags, fc);
-		__super_lock_excl(s);
 		if (!error)
 			error = fill_super(s, fc);
 		if (error) {
@@ -1653,15 +1645,7 @@ struct dentry *mount_bdev(struct file_system_type *fs_type,
 			return ERR_PTR(-EBUSY);
 		}
 	} else {
-		/*
-		 * We drop s_umount here because we need to open the bdev and
-		 * bdev->open_mutex ranks above s_umount (blkdev_put() ->
-		 * bdev_mark_dead()). It is safe because we have active sb
-		 * reference and SB_BORN is not set yet.
-		 */
-		super_unlock_excl(s);
 		error = setup_bdev_super(s, flags, NULL);
-		__super_lock_excl(s);
 		if (!error)
 			error = fill_super(s, data, flags & SB_SILENT ? 1 : 0);
 		if (error) {