linux-kernel - [PATCH] sched/fair: Fix call walk_tg_tree_from() without hold rcu

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Date:   Mon,  6 Apr 2020 20:10:08 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     mingo@...nel.org, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org
Cc:     linux-kernel@...r.kernel.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        Muchun Song <songmuchun@...edance.com>
Subject: [PATCH] sched/fair: Fix call walk_tg_tree_from() without hold rcu_lock

The walk_tg_tree_from() caller must hold rcu_lock, but the caller
do not call rcu_read_lock() in the unthrottle_cfs_rq(). The
unthrottle_cfs_rq() is used in 3 places. There are
distribute_cfs_runtime(), unthrottle_offline_cfs_rqs() and
tg_set_cfs_bandwidth(). The former 2 already hold the rcu lock,
but the last one does not. So fix it with calling rcu_read_lock()
in the unthrottle_cfs_rq().

Signed-off-by: Muchun Song <songmuchun@...edance.com>
---
 kernel/sched/fair.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6f05843c76d7d..870853c47b63c 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4782,7 +4782,9 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
 	raw_spin_unlock(&cfs_b->lock);
 
 	/* update hierarchical throttle state */
+	rcu_read_lock();
 	walk_tg_tree_from(cfs_rq->tg, tg_nop, tg_unthrottle_up, (void *)rq);
+	rcu_read_unlock();
 
 	if (!cfs_rq->load.weight)
 		return;
-- 
2.11.0