Commit c02aa73b authored by Darren Hart's avatar Darren Hart Committed by Ingo Molnar

sched: Allow users with sufficient RLIMIT_NICE to change from SCHED_IDLE policy

The current scheduler implementation returns -EPERM when trying to
change from SCHED_IDLE to SCHED_OTHER or SCHED_BATCH. Since SCHED_IDLE
is considered to be a nice 20 on steroids, changing to another policy
should be allowed provided the RLIMIT_NICE is accounted for.

This patch allows the following test-case to pass with RLIMIT_NICE=40,
but still fail with RLIMIT_NICE=10 when the calling process is run
from a typical shell (nice 0, or 20 in rlimit terms).

int main()
{
	int ret;
	struct sched_param sp;
	sp.sched_priority = 0;

	/* switch to SCHED_IDLE */
	ret = sched_setscheduler(0, SCHED_IDLE, &sp);
	printf("setscheduler IDLE: %d\n", ret);
	if (ret) return ret;

	/* switch back to SCHED_OTHER */
	ret = sched_setscheduler(0, SCHED_OTHER, &sp);
	printf("setscheduler OTHER: %d\n", ret);

	return ret;
}

 $ ulimit -e
 40
 $ ./test
 setscheduler IDLE: 0
 setscheduler OTHER: 0

 $ ulimit -e 10
 $ ulimit -e
 10
 $ ./test
 setscheduler IDLE: 0
 setscheduler OTHER: -1
Signed-off-by: default avatarDarren Hart <dvhart@linux.intel.com>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Richard Purdie <richard.purdie@linuxfoundation.org>
LKML-Reference: <4D657BEE.4040608@linux.intel.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent a2f5c9ab
...@@ -4981,12 +4981,15 @@ static int __sched_setscheduler(struct task_struct *p, int policy, ...@@ -4981,12 +4981,15 @@ static int __sched_setscheduler(struct task_struct *p, int policy,
param->sched_priority > rlim_rtprio) param->sched_priority > rlim_rtprio)
return -EPERM; return -EPERM;
} }
/* /*
* Like positive nice levels, dont allow tasks to * Treat SCHED_IDLE as nice 20. Only allow a switch to
* move out of SCHED_IDLE either: * SCHED_NORMAL if the RLIMIT_NICE would normally permit it.
*/ */
if (p->policy == SCHED_IDLE && policy != SCHED_IDLE) if (p->policy == SCHED_IDLE && policy != SCHED_IDLE) {
return -EPERM; if (!can_nice(p, TASK_NICE(p)))
return -EPERM;
}
/* can't change other user's priorities */ /* can't change other user's priorities */
if (!check_same_owner(p)) if (!check_same_owner(p))
......
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