Commit 01e86182 authored by Brian Silverman's avatar Brian Silverman Committed by Ben Hutchings

sched: Fix RLIMIT_RTTIME when PI-boosting to RT

commit 746db944 upstream.

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: default avatarBrian Silverman <brian@peloton-tech.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: austin@peloton-tech.com
Link: http://lkml.kernel.org/r/1424305436-6716-1-git-send-email-brian@peloton-tech.comSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
[bwh: Backported to 3.2: adjust filename, context]
Signed-off-by: default avatarBen Hutchings <ben@decadent.org.uk>
parent f3022d3d
......@@ -5224,8 +5224,11 @@ void rt_mutex_setprio(struct task_struct *p, int prio)
if (rt_prio(prio))
p->sched_class = &rt_sched_class;
else
else {
if (rt_prio(oldprio))
p->rt.timeout = 0;
p->sched_class = &fair_sched_class;
}
p->prio = prio;
......
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