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: Darren Hart <dvhart@linux.intel.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Richard Purdie <richard.purdie@linuxfoundation.org>
LKML-Reference: <4D657BEE.4040608@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/sched.c b/kernel/sched.c
index 0c87126..f303070 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4981,12 +4981,15 @@
param->sched_priority > rlim_rtprio)
return -EPERM;
}
+
/*
- * Like positive nice levels, dont allow tasks to
- * move out of SCHED_IDLE either:
+ * Treat SCHED_IDLE as nice 20. Only allow a switch to
+ * SCHED_NORMAL if the RLIMIT_NICE would normally permit it.
*/
- if (p->policy == SCHED_IDLE && policy != SCHED_IDLE)
- return -EPERM;
+ if (p->policy == SCHED_IDLE && policy != SCHED_IDLE) {
+ if (!can_nice(p, TASK_NICE(p)))
+ return -EPERM;
+ }
/* can't change other user's priorities */
if (!check_same_owner(p))
