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SubjectRe: [powerpc][5.13.0-rc7] Kernel warning (kernel/sched/fair.c:401) while running LTP tests
Hi,

Did some more research, and it looks like this is what happens:

$ tree /sys/fs/cgroup/ltp/ -d --charset=ascii
/sys/fs/cgroup/ltp/
|-- drain
`-- test-6851
`-- level2
|-- level3a
| |-- worker1
| `-- worker2
`-- level3b
`-- worker3

Timeline (ish):
- worker3 gets throttled
- level3b is decayed, since it has no more load
- level2 get throttled
- worker3 get unthrottled
- level2 get unthrottled
- worker3 is added to list
- level3b is not added to list, since nr_running==0 and is decayed


The attached diff (based on
https://lore.kernel.org/lkml/20210518125202.78658-3-odin@uged.al/)
fixes the issue for me. Not the most elegant solution, but the
simplest one as of now, and to show what is wrong.

Any thoughts Vincent?

Thanks
Odin


diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index bfaa6e1f6067..aa32e9c29efd 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -376,7 +376,8 @@ static inline bool list_add_leaf_cfs_rq(struct
cfs_rq *cfs_rq)
return false;
}

-static inline void list_del_leaf_cfs_rq(struct cfs_rq *cfs_rq)
+/* Returns 1 if cfs_rq was present in the list and removed */
+static inline bool list_del_leaf_cfs_rq(struct cfs_rq *cfs_rq)
{
if (cfs_rq->on_list) {
struct rq *rq = rq_of(cfs_rq);
@@ -393,7 +394,9 @@ static inline void list_del_leaf_cfs_rq(struct
cfs_rq *cfs_rq)

list_del_rcu(&cfs_rq->leaf_cfs_rq_list);
cfs_rq->on_list = 0;
+ return 1;
}
+ return 0;
}

static inline void assert_list_leaf_cfs_rq(struct rq *rq)
@@ -3298,24 +3301,6 @@ static inline void cfs_rq_util_change(struct
cfs_rq *cfs_rq, int flags)

#ifdef CONFIG_SMP
#ifdef CONFIG_FAIR_GROUP_SCHED
-
-static inline bool cfs_rq_is_decayed(struct cfs_rq *cfs_rq)
-{
- if (cfs_rq->load.weight)
- return false;
-
- if (cfs_rq->avg.load_sum)
- return false;
-
- if (cfs_rq->avg.util_sum)
- return false;
-
- if (cfs_rq->avg.runnable_sum)
- return false;
-
- return true;
-}
-
/**
* update_tg_load_avg - update the tg's load avg
* @cfs_rq: the cfs_rq whose avg changed
@@ -4109,11 +4094,6 @@ static inline void update_misfit_status(struct
task_struct *p, struct rq *rq)

#else /* CONFIG_SMP */

-static inline bool cfs_rq_is_decayed(struct cfs_rq *cfs_rq)
-{
- return true;
-}
-
#define UPDATE_TG 0x0
#define SKIP_AGE_LOAD 0x0
#define DO_ATTACH 0x0
@@ -4771,10 +4751,11 @@ static int tg_unthrottle_up(struct task_group
*tg, void *data)
if (!cfs_rq->throttle_count) {
cfs_rq->throttled_clock_task_time += rq_clock_task(rq) -
cfs_rq->throttled_clock_task;
-
- /* Add cfs_rq with load or one or more already running
entities to the list */
- if (!cfs_rq_is_decayed(cfs_rq) || cfs_rq->nr_running)
+ if (cfs_rq->insert_on_unthrottle) {
list_add_leaf_cfs_rq(cfs_rq);
+ if (tg->parent)
+
tg->parent->cfs_rq[cpu_of(rq)]->insert_on_unthrottle = true;
+ }
}

return 0;
@@ -4788,7 +4769,7 @@ static int tg_throttle_down(struct task_group
*tg, void *data)
/* group is entering throttled state, stop time */
if (!cfs_rq->throttle_count) {
cfs_rq->throttled_clock_task = rq_clock_task(rq);
- list_del_leaf_cfs_rq(cfs_rq);
+ cfs_rq->insert_on_unthrottle = list_del_leaf_cfs_rq(cfs_rq);
}
cfs_rq->throttle_count++;

@@ -8019,6 +8000,23 @@ static bool __update_blocked_others(struct rq
*rq, bool *done)

#ifdef CONFIG_FAIR_GROUP_SCHED

+static inline bool cfs_rq_is_decayed(struct cfs_rq *cfs_rq)
+{
+ if (cfs_rq->load.weight)
+ return false;
+
+ if (cfs_rq->avg.load_sum)
+ return false;
+
+ if (cfs_rq->avg.util_sum)
+ return false;
+
+ if (cfs_rq->avg.runnable_sum)
+ return false;
+
+ return true;
+}
+
static bool __update_blocked_fair(struct rq *rq, bool *done)
{
struct cfs_rq *cfs_rq, *pos;
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index a189bec13729..12a707d99ee6 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -602,6 +602,7 @@ struct cfs_rq {
u64 throttled_clock_task_time;
int throttled;
int throttle_count;
+ int insert_on_unthrottle;
struct list_head throttled_list;
#endif /* CONFIG_CFS_BANDWIDTH */
#endif /* CONFIG_FAIR_GROUP_SCHED */
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