linux-kernel - [tip: sched/core] sched/cpuacct: Remove redundant RCU read lock

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Date:   Tue, 01 Mar 2022 15:24:41 -0000
From:   "tip-bot2 for Chengming Zhou" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Tejun Heo <tj@...nel.org>,
        Chengming Zhou <zhouchengming@...edance.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: sched/core] sched/cpuacct: Remove redundant RCU read lock

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     3eba0505d03a9c1eb30d40c2330c0880b22d1b3a
Gitweb:        https://git.kernel.org/tip/3eba0505d03a9c1eb30d40c2330c0880b22d1b3a
Author:        Chengming Zhou <zhouchengming@...edance.com>
AuthorDate:    Sun, 20 Feb 2022 13:14:26 +08:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Tue, 01 Mar 2022 16:18:38 +01:00

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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lore.kernel.org/r/20220220051426.5274-3-zhouchengming@bytedance.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 9a109c6..1e356c2 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 f79f884..d269ede 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 = {