linux-kernel - [PATCH v3 3/3] sched/cpuacct: remove redundant RCU read lock

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Date:   Sun, 20 Feb 2022 13:14:26 +0800
From:   Chengming Zhou <zhouchengming@...edance.com>
To:     mingo@...hat.com, peterz@...radead.org, vincent.guittot@...aro.org,
        bristot@...hat.com, zhaolei@...fujitsu.com, tj@...nel.org,
        lizefan.x@...edance.com, hannes@...xchg.org
Cc:     linux-kernel@...r.kernel.org,
        Chengming Zhou <zhouchengming@...edance.com>
Subject: [PATCH v3 3/3] sched/cpuacct: remove redundant RCU read lock

The cpuacct_account_field() and it's cgroup v2 wrapper
cgroup_account_cputime_field() is only called from cputime
in task_group_account_field(), which is already in RCU read-side
critical section. So remove these redundant RCU read lock.

Suggested-by: Tejun Heo <tj@...nel.org>
Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
---
 include/linux/cgroup.h | 2 --
 kernel/sched/cpuacct.c | 2 --
 2 files changed, 4 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 9a109c6ac0e0..1e356c222756 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -804,11 +804,9 @@ static inline void cgroup_account_cputime_field(struct task_struct *task,
 
 	cpuacct_account_field(task, index, delta_exec);
 
-	rcu_read_lock();
 	cgrp = task_dfl_cgroup(task);
 	if (cgroup_parent(cgrp))
 		__cgroup_account_cputime_field(cgrp, index, delta_exec);
-	rcu_read_unlock();
 }
 
 #else	/* CONFIG_CGROUPS */
diff --git a/kernel/sched/cpuacct.c b/kernel/sched/cpuacct.c
index f79f88456d72..d269ede84e85 100644
--- a/kernel/sched/cpuacct.c
+++ b/kernel/sched/cpuacct.c
@@ -352,10 +352,8 @@ void cpuacct_account_field(struct task_struct *tsk, int index, u64 val)
 {
 	struct cpuacct *ca;
 
-	rcu_read_lock();
 	for (ca = task_ca(tsk); ca != &root_cpuacct; ca = parent_ca(ca))
 		__this_cpu_add(ca->cpustat->cpustat[index], val);
-	rcu_read_unlock();
 }
 
 struct cgroup_subsys cpuacct_cgrp_subsys = {
-- 
2.20.1