linux-kernel - [PATCH] cpu: Remove obsolete comment from takedown

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Message-ID: <20250729191232.664931-1-longman@redhat.com>
Date: Tue, 29 Jul 2025 15:12:32 -0400
From: Waiman Long <longman@...hat.com>
To: Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>
Cc: linux-kernel@...r.kernel.org,
	Waiman Long <longman@...hat.com>
Subject: [PATCH] cpu: Remove obsolete comment from takedown_cpu()

takedown_cpu() has a comment about "all preempt/rcu users must observe
!cpu_active()" which is kind of meaningless in this function. This
comment was originally introduced by commit 6acce3ef8452 ("sched: Remove
get_online_cpus() usage") when _cpu_down() was setting cpu_active_mask
and synchronize_rcu()/synchronize_sched() were added after that.

Later commit 40190a78f85f ("sched/hotplug: Convert cpu_[in]active
notifiers to state machine") added a new CPUHP_AP_ACTIVE hotplug
state to set/clear cpu_active_mask. The following commit b2454caa8977
("sched/hotplug: Move sync_rcu to be with set_cpu_active(false)")
move the synchronize_*() calls to sched_cpu_deactivate() associated
with the new hotplug state, but left the comment behind.

Remove this comment as it is no longer relevant in takedown_cpu().

Signed-off-by: Waiman Long <longman@...hat.com>
---
 kernel/cpu.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index a59e009e0be4..2addcba38c1a 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1308,9 +1308,6 @@ static int takedown_cpu(unsigned int cpu)
 	 */
 	irq_lock_sparse();

-	/*
-	 * So now all preempt/rcu users must observe !cpu_active().
-	 */
 	err = stop_machine_cpuslocked(take_cpu_down, NULL, cpumask_of(cpu));
 	if (err) {
 		/* CPU refused to die */
-- 
2.50.0