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Subject[patch] sched: add locking when update the task_group's cfs_rq[] array.
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add locking when update the task_group's cfs_rq[] array.  tg_shares_up()
can be potentially executed concurrently on multiple CPUs with overlaping
cpu mask depending on where task_cpu() was when a task got woken up. Lack
of any locking while redistribute tg->shares over cfs_rq[] array opens up
a large window for conflict updates and utimately cause corruptions to the
integrity of per cpu cfs_rq shares. Add a tg_lock to protect the operations.


Signed-off-by: Ken Chen <kenchen@google.com>

diff --git a/kernel/sched.c b/kernel/sched.c
index 1ff78b6..907a44e 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -267,6 +267,8 @@ struct task_group {
/* runqueue "owned" by this group on each cpu */
struct cfs_rq **cfs_rq;
unsigned long shares;
+ /* protect integrity of per-cpu cfs_rq[i]->shares */
+ spinlock_t tg_lock;
#endif

#ifdef CONFIG_RT_GROUP_SCHED
@@ -1493,13 +1495,11 @@ update_group_shares_cpu
if (abs(shares - tg->se[cpu]->load.weight) >
sysctl_sched_shares_thresh) {
struct rq *rq = cpu_rq(cpu);
- unsigned long flags;

- spin_lock_irqsave(&rq->lock, flags);
+ spin_lock(&rq->lock);
tg->cfs_rq[cpu]->shares = shares;
-
__set_se_shares(tg->se[cpu], shares);
- spin_unlock_irqrestore(&rq->lock, flags);
+ spin_unlock(&rq->lock);
}
}

@@ -1513,8 +1513,12 @@ static int tg_shares_up
unsigned long weight, rq_weight = 0;
unsigned long shares = 0;
struct sched_domain *sd = data;
+ unsigned long flags;
int i;

+ if (!spin_trylock_irqsave(&tg->tg_lock, flags))
+ return 0;
+
for_each_cpu_mask(i, sd->span) {
/*
* If there are currently no tasks on the cpu pretend there
@@ -1539,6 +1543,7 @@ static int tg_shares_up
for_each_cpu_mask(i, sd->span)
update_group_shares_cpu(tg, i, shares, rq_weight);

+ spin_unlock_irqrestore(&tg->tg_lock, flags);
return 0;
}

@@ -8195,6 +8200,10 @@ void __init sched_init(void)
list_add(&init_task_group.list, &task_groups);
INIT_LIST_HEAD(&init_task_group.children);

+#ifdef CONFIG_FAIR_GROUP_SCHED
+ spin_lock_init(&init_task_group.tg_lock);
+#endif /* CONFIG_FAIR_GROUP_SCHED */
+
#ifdef CONFIG_USER_SCHED
INIT_LIST_HEAD(&root_task_group.children);
init_task_group.parent = &root_task_group;
@@ -8491,6 +8500,10 @@ int alloc_fair_sched_group

tg->shares = NICE_0_LOAD;

+#ifdef CONFIG_FAIR_GROUP_SCHED
+ spin_lock_init(&tg->tg_lock);
+#endif /* CONFIG_FAIR_GROUP_SCHED */
+
for_each_possible_cpu(i) {
rq = cpu_rq(i);

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