From c02aa73b1d18e43cfd79c2f193b225e84ca497c8 Mon Sep 17 00:00:00 2001 From: Darren Hart Date: Thu, 17 Feb 2011 15:37:07 -0800 Subject: [PATCH] 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 Signed-off-by: Peter Zijlstra Cc: Richard Purdie LKML-Reference: <4D657BEE.4040608@linux.intel.com> Signed-off-by: Ingo Molnar --- kernel/sched.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) 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 @@ recheck: 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)) -- 2.7.4