sched: Make sched_class::get_rr_interval() optional

Not all classes implement (or can implement) a useful get_rr_interval()
function, default to a 0 time-slice for them.

This fixes a crash reported by Tommi Rantala.

Reported-by: Tommi Rantala <tt.rantala@gmail.com>
Cc: Dave Jones <davej@redhat.com>
Cc: Tommi Rantala <tt.rantala@gmail.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20140127105413.GC11314@laptop.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 3 insertions, 1 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 36c951b7eef8..81343d6bd9cb 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4324,7 +4324,9 @@ SYSCALL_DEFINE2(sched_rr_get_interval, pid_t, pid,
                 goto out_unlock;
 
         rq = task_rq_lock(p, &flags);
-        time_slice = p->sched_class->get_rr_interval(rq, p);
+        time_slice = 0;
+        if (p->sched_class->get_rr_interval)
+                time_slice = p->sched_class->get_rr_interval(rq, p);
         task_rq_unlock(rq, p, &flags);
 
         rcu_read_unlock();