sched: Preserve the nice level over sched_setscheduler() and sched_setparam() calls

Previously sched_setscheduler() and sched_setparam() would not affect
the nice value of a task, restore this behaviour.

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: raistlin@linux.it
Cc: juri.lelli@gmail.com
Cc: Michael wang <wangyun@linux.vnet.ibm.com>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Fixes: d50dde5a10f3 ("sched: Add new scheduler syscalls to support an extended scheduling parameters ABI")
Link: http://lkml.kernel.org/r/20140115113015.GB31570@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/sched/core.c

@@ -3451,7 +3451,8 @@ int sched_setscheduler(struct task_struct *p, int policy,
 {
 	struct sched_attr attr = {
 		.sched_policy   = policy,
-		.sched_priority = param->sched_priority
+		.sched_priority = param->sched_priority,
+		.sched_nice	= PRIO_TO_NICE(p->static_prio),
 	};
 	return __sched_setscheduler(p, &attr, true);
 }
@@ -3481,7 +3482,8 @@ int sched_setscheduler_nocheck(struct task_struct *p, int policy,
 {
 	struct sched_attr attr = {
 		.sched_policy   = policy,
-		.sched_priority = param->sched_priority
+		.sched_priority = param->sched_priority,
+		.sched_nice	= PRIO_TO_NICE(p->static_prio),
 	};
 	return __sched_setscheduler(p, &attr, false);
 }