__sched_setscheduler: don't do any policy checks when not "user"

The "user" parameter to __sched_setscheduler indicates whether the
change is being done on behalf of a user process or not.  If not, we
shouldn't apply any permissions checks, so don't call
security_task_setscheduler().
Signed-off-by: Jeremy Fitzhardinge <jeremy@goop.org>
Tested-by: Steve Wise <swise@opengridcomputing.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/sched.c

@@ -5004,19 +5004,21 @@ static int __sched_setscheduler(struct task_struct *p, int policy,
 			return -EPERM;
 	}
 
+	if (user) {
 #ifdef CONFIG_RT_GROUP_SCHED
-	/*
-	 * Do not allow realtime tasks into groups that have no runtime
-	 * assigned.
-	 */
-	if (user
-	    && rt_policy(policy) && task_group(p)->rt_bandwidth.rt_runtime == 0)
-		return -EPERM;
+		/*
+		 * Do not allow realtime tasks into groups that have no runtime
+		 * assigned.
+		 */
+		if (rt_policy(policy) && task_group(p)->rt_bandwidth.rt_runtime == 0)
+			return -EPERM;
 #endif
 
-	retval = security_task_setscheduler(p, policy, param);
-	if (retval)
-		return retval;
+		retval = security_task_setscheduler(p, policy, param);
+		if (retval)
+			return retval;
+	}
+
 	/*
 	 * make sure no PI-waiters arrive (or leave) while we are
 	 * changing the priority of the task: