linux-kernel - [PATCH v3 09/14] cgroup/cpuset: Remove redundant rcu_read_lock/unlock() in spin

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Message-Id: <20250916044735.2316171-10-dolinux.peng@gmail.com>
Date: Tue, 16 Sep 2025 12:47:30 +0800
From: pengdonglin <dolinux.peng@...il.com>
To: tj@...nel.org,
	tony.luck@...el.com,
	jani.nikula@...ux.intel.com,
	ap420073@...il.com,
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Cc: bigeasy@...utronix.de,
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	paulmck@...nel.org,
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	pengdonglin <dolinux.peng@...il.com>,
	Johannes Weiner <hannes@...xchg.org>,
	pengdonglin <pengdonglin@...omi.com>
Subject: [PATCH v3 09/14] cgroup/cpuset: Remove redundant rcu_read_lock/unlock() in spin_lock

From: pengdonglin <pengdonglin@...omi.com>

Since commit a8bb74acd8efe ("rcu: Consolidate RCU-sched update-side function definitions")
there is no difference between rcu_read_lock(), rcu_read_lock_bh() and
rcu_read_lock_sched() in terms of RCU read section and the relevant grace
period. That means that spin_lock(), which implies rcu_read_lock_sched(),
also implies rcu_read_lock().

There is no need no explicitly start a RCU read section if one has already
been started implicitly by spin_lock().

Simplify the code and remove the inner rcu_read_lock() invocation.

Cc: Waiman Long <longman@...hat.com>
Cc: Johannes Weiner <hannes@...xchg.org>
Acked-by: Waiman Long <longman@...hat.com>
Signed-off-by: pengdonglin <pengdonglin@...omi.com>
Signed-off-by: pengdonglin <dolinux.peng@...il.com>
---
 kernel/cgroup/cpuset.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 27adb04df675..9b7e8e8e9411 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -4073,7 +4073,6 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask)
 	struct cpuset *cs;
 
 	spin_lock_irqsave(&callback_lock, flags);
-	rcu_read_lock();
 
 	cs = task_cs(tsk);
 	if (cs != &top_cpuset)
@@ -4095,7 +4094,6 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask)
 			cpumask_copy(pmask, possible_mask);
 	}
 
-	rcu_read_unlock();
 	spin_unlock_irqrestore(&callback_lock, flags);
 }
 
@@ -4168,9 +4166,7 @@ nodemask_t cpuset_mems_allowed(struct task_struct *tsk)
 	unsigned long flags;
 
 	spin_lock_irqsave(&callback_lock, flags);
-	rcu_read_lock();
 	guarantee_online_mems(task_cs(tsk), &mask);
-	rcu_read_unlock();
 	spin_unlock_irqrestore(&callback_lock, flags);
 
 	return mask;
@@ -4265,10 +4261,8 @@ bool cpuset_current_node_allowed(int node, gfp_t gfp_mask)
 	/* Not hardwall and node outside mems_allowed: scan up cpusets */
 	spin_lock_irqsave(&callback_lock, flags);
 
-	rcu_read_lock();
 	cs = nearest_hardwall_ancestor(task_cs(current));
 	allowed = node_isset(node, cs->mems_allowed);
-	rcu_read_unlock();
 
 	spin_unlock_irqrestore(&callback_lock, flags);
 	return allowed;
-- 
2.34.1