Commit 746db944 authored Feb 18, 2015 by Brian Silverman Committed by Ingo Molnar Mar 23, 2015

sched: Fix RLIMIT_RTTIME when PI-boosting to RT



When non-realtime tasks get priority-inheritance boosted to a realtime
scheduling class, RLIMIT_RTTIME starts to apply to them. However, the
counter used for checking this (the same one used for SCHED_RR
timeslices) was not getting reset. This meant that tasks running with a
non-realtime scheduling class which are repeatedly boosted to a realtime
one, but never block while they are running realtime, eventually hit the
timeout without ever running for a time over the limit. This patch
resets the realtime timeslice counter when un-PI-boosting from an RT to
a non-RT scheduling class.

I have some test code with two threads and a shared PTHREAD_PRIO_INHERIT
mutex which induces priority boosting and spins while boosted that gets
killed by a SIGXCPU on non-fixed kernels but doesn't with this patch
applied. It happens much faster with a CONFIG_PREEMPT_RT kernel, and
does happen eventually with PREEMPT_VOLUNTARY kernels.

Signed-off-by: Brian Silverman <brian@peloton-tech.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: austin@peloton-tech.com
Cc: <stable@vger.kernel.org>
Link: http://lkml.kernel.org/r/1424305436-6716-1-git-send-email-brian@peloton-tech.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent bc465aa9

kernel/sched/core.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -3034,6 +3034,8 @@ void rt_mutex_setprio(struct task_struct *p, int prio)
		} else {
		if (dl_prio(oldprio))
		p->dl.dl_boosted = 0;
		if (rt_prio(oldprio))
		p->rt.timeout = 0;
		p->sched_class = &fair_sched_class;
		}

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