[PATCH 3.4 127/172] sched: Fix RLIMIT_RTTIME when PI-boosting to RT

From: lizf
Date: Tue Jun 16 2015 - 05:06:40 EST

From: Brian Silverman <brian@xxxxxxxxxxxxxxxx>

3.4.108-rc1 review patch. If anyone has any objections, please let me know.


commit 746db9443ea57fd9c059f62c4bfbf41cf224fe13 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: Brian Silverman <brian@xxxxxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: austin@xxxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/1424305436-6716-1-git-send-email-brian@xxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
[lizf: Backported to 3.4: adjust contest]
Signed-off-by: Zefan Li <lizefan@xxxxxxxxxx>
kernel/sched/core.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 5701cb9..2f8363e 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4031,10 +4031,13 @@ void rt_mutex_setprio(struct task_struct *p, int prio)
if (running)
p->sched_class->put_prev_task(rq, p);

- if (rt_prio(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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