sched: Fix up scheduler syscall LTP fails

Wu reported LTP failures:

  > ltp.sched_setparam02.1.TFAIL
  > ltp.sched_setparam02.2.TFAIL
  > ltp.sched_setparam02.3.TFAIL
  > ltp.sched_setparam03.1.TFAIL

There were 2 things wrong; firstly __setscheduler() failed on
sched_setparam()'s policy = -1, fix that by reading from p->policy in
that case.

Secondly, getparam() (and getattr()) would still report !0
sched_priority for !FIFO/RR tasks after having been such. So
unconditionally set p->rt_priority.

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@gmail.com>
Cc: Dario Faggioli <raistlin@linux.it>
Fixes: d50dde5a10f3 ("sched: Add new scheduler syscalls to support an extended scheduling parameters ABI")
Link: http://lkml.kernel.org/r/20140115153320.GH31570@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/sched/core.c

@@ -3172,15 +3172,23 @@ static void __setscheduler(struct rq *rq, struct task_struct *p,
 {
 	int policy = attr->sched_policy;
 
+	if (policy == -1) /* setparam */
+		policy = p->policy;
+
 	p->policy = policy;
 
 	if (dl_policy(policy))
 		__setparam_dl(p, attr);
-	else if (rt_policy(policy))
-		p->rt_priority = attr->sched_priority;
-	else
+	else if (fair_policy(policy))
 		p->static_prio = NICE_TO_PRIO(attr->sched_nice);
 
+	/*
+	 * __sched_setscheduler() ensures attr->sched_priority == 0 when
+	 * !rt_policy. Always setting this ensures that things like
+	 * getparam()/getattr() don't report silly values for !rt tasks.
+	 */
+	p->rt_priority = attr->sched_priority;
+
 	p->normal_prio = normal_prio(p);
 	p->prio = rt_mutex_getprio(p);