linux-kernel - Re: Bug in scheduler when using rt

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Date:	Mon, 17 Jan 2011 17:00:32 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	samu.p.onkalo@...ia.com
Cc:	mingo@...e.hu,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	tglx <tglx@...utronix.de>
Subject: Re: Bug in scheduler when using rt_mutex

On Mon, 2011-01-17 at 16:42 +0200, Onkalo Samu wrote:
> 
> Failure case:
> - user process locks rt_mutex
> - and goes to sleep (wait_for_completion etc.)
> - user process is dequeued to sleep state
> -> vruntime is not updated in dequeue_entity
> 

Does the below (completely untested) patch help?

---
 kernel/sched.c      |    6 +++++-
 kernel/sched_fair.c |   11 +++++++++++
 2 files changed, 16 insertions(+), 1 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index a0eb094..be09581 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -8108,8 +8108,10 @@ EXPORT_SYMBOL(__might_sleep);
 #ifdef CONFIG_MAGIC_SYSRQ
 static void normalize_task(struct rq *rq, struct task_struct *p)
 {
+	struct sched_class *prev_class = p->sched_class;
+	int old_prio = p->prio;
 	int on_rq;
-
+       
 	on_rq = p->se.on_rq;
 	if (on_rq)
 		deactivate_task(rq, p, 0);
@@ -8118,6 +8120,8 @@ static void normalize_task(struct rq *rq, struct task_struct *p)
 		activate_task(rq, p, 0);
 		resched_task(rq->curr);
 	}
+
+	check_class_changed(rq, p, prev_class, old_prio, task_current(rq, p));
 }
 
 void normalize_rt_tasks(void)
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index c62ebae..0a27b00 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -4072,6 +4072,17 @@ static void prio_changed_fair(struct rq *rq, struct task_struct *p,
 static void switched_to_fair(struct rq *rq, struct task_struct *p,
 			     int running)
 {
+	struct sched_entity *se = &p->se;
+	struct cfs_rq *cfs_rq = cfs_rq_of(se);
+
+	if (se->on_rq && cfs_rq->curr != se)
+		__dequeue_entity(cfs_rq, se);
+
+	place_entity(cfs_rq, se, 0);
+
+	if (se->on_rq && cfs_rq->curr != se)
+		__enqueue_entity(cfs_rq, se);
+
 	/*
 	 * We were most likely switched from sched_rt, so
 	 * kick off the schedule if running, otherwise just see

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