[PATCH] sched_rt: fix overload bug on rt group scheduling -v2

From: Peter Zijlstra
Date: Wed Jul 08 2009 - 11:38:31 EST


Greg, how's this?

---
Subject: sched_rt: fix overload bug on rt group scheduling
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Wed, 01 Apr 2009 18:40:15 +0200

Fixes an easily triggerable BUG() when setting process affinities.

Make sure to count the number of migratable tasks in the same place:
the root rt_rq. Otherwise the number doesn't make sense and we'll hit
the BUG in set_cpus_allowed_rt().

Also, make sure we only count tasks, not groups (this is probably
already taken care of by the fact that rt_se->nr_cpus_allowed will be 0
for groups, but be more explicit)

Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
---
kernel/sched_rt.c | 18 +++++++++++++++++-
1 file changed, 17 insertions(+), 1 deletion(-)

Index: linux-2.6/kernel/sched_rt.c
===================================================================
--- linux-2.6.orig/kernel/sched_rt.c
+++ linux-2.6/kernel/sched_rt.c
@@ -10,6 +10,8 @@ static inline struct task_struct *rt_tas

#ifdef CONFIG_RT_GROUP_SCHED

+#define rt_entity_is_task(rt_se) (!(rt_se)->my_q)
+
static inline struct rq *rq_of_rt_rq(struct rt_rq *rt_rq)
{
return rt_rq->rq;
@@ -22,6 +24,8 @@ static inline struct rt_rq *rt_rq_of_se(

#else /* CONFIG_RT_GROUP_SCHED */

+#define rt_entity_is_task(rt_se) (1)
+
static inline struct rq *rq_of_rt_rq(struct rt_rq *rt_rq)
{
return container_of(rt_rq, struct rq, rt);
@@ -73,7 +77,7 @@ static inline void rt_clear_overload(str

static void update_rt_migration(struct rt_rq *rt_rq)
{
- if (rt_rq->rt_nr_migratory && (rt_rq->rt_nr_running > 1)) {
+ if (rt_rq->rt_nr_migratory && rt_rq->rt_nr_total > 1) {
if (!rt_rq->overloaded) {
rt_set_overload(rq_of_rt_rq(rt_rq));
rt_rq->overloaded = 1;
@@ -86,6 +90,12 @@ static void update_rt_migration(struct r

static void inc_rt_migration(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
{
+ if (!rt_entity_is_task(rt_se))
+ return;
+
+ rt_rq = &rq_of_rt_rq(rt_rq)->rt;
+
+ rt_rq->rt_nr_total++;
if (rt_se->nr_cpus_allowed > 1)
rt_rq->rt_nr_migratory++;

@@ -94,6 +104,12 @@ static void inc_rt_migration(struct sche

static void dec_rt_migration(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
{
+ if (!rt_entity_is_task(rt_se))
+ return;
+
+ rt_rq = &rq_of_rt_rq(rt_rq)->rt;
+
+ rt_rq->rt_nr_total--;
if (rt_se->nr_cpus_allowed > 1)
rt_rq->rt_nr_migratory--;

diff --git a/kernel/sched.c b/kernel/sched.c
index fd3ac58..a07d520 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -493,6 +493,7 @@ struct rt_rq {
#endif
#ifdef CONFIG_SMP
unsigned long rt_nr_migratory;
+ unsigned long rt_nr_total;
int overloaded;
struct plist_head pushable_tasks;
#endif

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