devpts: Must release s_umount on error

We should drop the ->s_umount mutex if an error occurs after the
sget()/grab_super() call. This was introduced when adding support
for multiple instances of devpts and noticed during a code review/reorg.
Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/devpts/inode.c

@@ -385,6 +385,7 @@ static int new_pts_mount(struct file_system_type *fs_type, int flags,
 
 fail:
 	dput(mnt->mnt_sb->s_root);
+	up_write(&mnt->mnt_sb->s_umount);
 	deactivate_super(mnt->mnt_sb);
 	return err;
 }
@@ -473,6 +474,7 @@ static int init_pts_mount(struct file_system_type *fs_type, int flags,
 	err = mknod_ptmx(mnt->mnt_sb);
 	if (err) {
 		dput(mnt->mnt_sb->s_root);
+		up_write(&mnt->mnt_sb->s_umount);
 		deactivate_super(mnt->mnt_sb);
 	}