sched: fix crash in sys_sched_rr_get_interval()

Luiz Fernando N. Capitulino reported that sched_rr_get_interval()
crashes for SCHED_OTHER tasks that are on an idle runqueue.

The fix is to return a 0 timeslice for tasks that are on an idle
runqueue. (and which are not running, obviously)

this also shrinks the code a bit:

   text    data     bss     dec     hex filename
  47903    3934     336   52173    cbcd sched.o.before
  47885    3934     336   52155    cbbb sched.o.after

Reported-by: Luiz Fernando N. Capitulino <lcapitulino@mandriva.com.br>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/sched.c b/kernel/sched.c
index 59ff6b1..b062856 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4850,17 +4850,21 @@ long sys_sched_rr_get_interval(pid_t pid, struct timespec __user *interval)
        if (retval)
                goto out_unlock;
 
-       if (p->policy == SCHED_FIFO)
-               time_slice = 0;
-       else if (p->policy == SCHED_RR)
+       /*
+        * Time slice is 0 for SCHED_FIFO tasks and for SCHED_OTHER
+        * tasks that are on an otherwise idle runqueue:
+        */
+       time_slice = 0;
+       if (p->policy == SCHED_RR) {
                time_slice = DEF_TIMESLICE;
-       else {
+       } else {
                struct sched_entity *se = &p->se;
                unsigned long flags;
                struct rq *rq;
 
                rq = task_rq_lock(p, &flags);
-               time_slice = NS_TO_JIFFIES(sched_slice(cfs_rq_of(se), se));
+               if (rq->cfs.load.weight)
+                       time_slice = NS_TO_JIFFIES(sched_slice(&rq->cfs, se));
                task_rq_unlock(rq, &flags);
        }
        read_unlock(&tasklist_lock);