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>
diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c
index bff4052..140b431 100644
--- a/fs/devpts/inode.c
+++ b/fs/devpts/inode.c
@@ -385,6 +385,7 @@
 
 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 @@
 	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);
 	}