pidns: rewrite copy_pid_ns()

copy_pid_ns() is a perfect example of a case where unwinding leads to more
code and makes it less clear.  Watch the diffstat.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Reviewed-by: Serge Hallyn <serue@us.ibm.com>
Acked-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Reviewed-by: WANG Cong <xiyou.wangcong@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/pid_namespace.c

@@ -116,23 +116,11 @@ static void destroy_pid_namespace(struct pid_namespace *ns)
 
 struct pid_namespace *copy_pid_ns(unsigned long flags, struct pid_namespace *old_ns)
 {
-	struct pid_namespace *new_ns;
-
-	BUG_ON(!old_ns);
-	new_ns = get_pid_ns(old_ns);
 	if (!(flags & CLONE_NEWPID))
-		goto out;
-
-	new_ns = ERR_PTR(-EINVAL);
+		return get_pid_ns(old_ns);
 	if (flags & CLONE_THREAD)
-		goto out_put;
-
-	new_ns = create_pid_namespace(old_ns);
-
-out_put:
-	put_pid_ns(old_ns);
-out:
-	return new_ns;
+		return ERR_PTR(-EINVAL);
+	return create_pid_namespace(old_ns);
 }
 
 void free_pid_ns(struct kref *kref)