sched_rt: Fix overload bug on rt group scheduling

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)

Tested-by: Thomas Gleixner <tglx@linutronix.de>
CC: stable@kernel.org
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Gregory Haskins <ghaskins@novell.com>
LKML-Reference: <1247067476.9777.57.camel@twins>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 18 insertions, 1 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 7c9098d186e6..a17f3d9a8bfa 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
diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index 9bf0d2a73045..3918e01994e0 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -10,6 +10,8 @@ static inline struct task_struct *rt_task_of(struct sched_rt_entity *rt_se)
 
 #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(struct sched_rt_entity *rt_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(struct rq *rq)
 
 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 rt_rq *rt_rq)
 
 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 sched_rt_entity *rt_se, struct rt_rq *rt_rq)
 
 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--;