* Luiz Fernando N. Capitulino <[email protected]> wrote:
> | The problem is on SMP: if sched_rr_get_interval() gets a task from
> | an otherwise idle runqueue, then rq->load.weight is 0. Normally
> | sched_slice() is only used on a busy runqueue. So the correct fixup
> | site is not in sched_slice() but in sys_sched_rr_get_interval() -
> | i'm working on the right fix, i hope to be able to send a pull
> | request in a few minutes.
>
> Ingo, I can reproduce this w/o SMP support as well.
hm, if you run this as an RT task, right? Or can you trigger it via pure
SCHED_OTHER tasks as well? Below is my candidate fix.
Ingo
--------------->
Subject: sched: fix crash in sys_sched_rr_get_interval()
From: Ingo Molnar <[email protected]>
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)
Reported-by: Luiz Fernando N. Capitulino <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
---
kernel/sched.c | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)
Index: linux/kernel/sched.c
===================================================================
--- linux.orig/kernel/sched.c
+++ linux/kernel/sched.c
@@ -4850,17 +4850,21 @@ long sys_sched_rr_get_interval(pid_t pid
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);
--
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