sched: Fix RLIMIT_RTTIME when PI-boosting to RT

brian-peloton · Ingo Molnar · commit 746db9443ea5 · 2015-03-23T10:47:55.000+01:00
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>
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
@@ -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;
 	}
 

Original file line number	Diff line number	Diff line change
`@@ -3034,6 +3034,8 @@ void rt_mutex_setprio(struct task_struct *p, int prio)`
`3034`	`3034`	`} else {`
`3035`	`3035`	`if (dl_prio(oldprio))`
`3036`	`3036`	`p->dl.dl_boosted = 0;`
	`3037`	`+ if (rt_prio(oldprio))`
	`3038`	`+ p->rt.timeout = 0;`
`3037`	`3039`	`p->sched_class = &fair_sched_class;`
`3038`	`3040`	`}`
`3039`	`3041`