linux-kernel - [PATCH 2/7] rcu: Remove swake_up_one

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Message-ID: <20250418161542.2429420-3-joelagnelf@nvidia.com>
Date: Fri, 18 Apr 2025 12:15:35 -0400
From: Joel Fernandes <joelagnelf@...dia.com>
To: linux-kernel@...r.kernel.org,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Frederic Weisbecker <frederic@...nel.org>,
	Neeraj Upadhyay <neeraj.upadhyay@...nel.org>,
	Joel Fernandes <joelagnelf@...dia.com>,
	Josh Triplett <josh@...htriplett.org>,
	Boqun Feng <boqun.feng@...il.com>,
	Uladzislau Rezki <urezki@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Zqiang <qiang.zhang1211@...il.com>
Cc: rcu@...r.kernel.org,
	Usama Arif <usamaarif642@...il.com>
Subject: [PATCH 2/7] rcu: Remove swake_up_one_online() bandaid

From: Frederic Weisbecker <frederic@...nel.org>

It's now ok to perform a wake-up from an offline CPU because the
resulting armed scheduler bandwidth hrtimers are now correctly targeted
by hrtimer infrastructure.

Remove the obsolete hackerry.

Link: https://lore.kernel.org/all/20241231170712.149394-3-frederic@kernel.org/
Reviewed-by: Usama Arif <usamaarif642@...il.com>
Reviewed-by: Joel Fernandes <joelagnelf@...dia.com>
Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
Signed-off-by: Joel Fernandes <joelagnelf@...dia.com>
---
 kernel/rcu/tree.c      | 34 +---------------------------------
 kernel/rcu/tree_exp.h  |  2 +-
 kernel/rcu/tree_nocb.h |  2 +-
 3 files changed, 3 insertions(+), 35 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 659f83e71048..1b8eee06183c 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1060,38 +1060,6 @@ static bool rcu_future_gp_cleanup(struct rcu_node *rnp)
 	return needmore;
 }
 
-static void swake_up_one_online_ipi(void *arg)
-{
-	struct swait_queue_head *wqh = arg;
-
-	swake_up_one(wqh);
-}
-
-static void swake_up_one_online(struct swait_queue_head *wqh)
-{
-	int cpu = get_cpu();
-
-	/*
-	 * If called from rcutree_report_cpu_starting(), wake up
-	 * is dangerous that late in the CPU-down hotplug process. The
-	 * scheduler might queue an ignored hrtimer. Defer the wake up
-	 * to an online CPU instead.
-	 */
-	if (unlikely(cpu_is_offline(cpu))) {
-		int target;
-
-		target = cpumask_any_and(housekeeping_cpumask(HK_TYPE_RCU),
-					 cpu_online_mask);
-
-		smp_call_function_single(target, swake_up_one_online_ipi,
-					 wqh, 0);
-		put_cpu();
-	} else {
-		put_cpu();
-		swake_up_one(wqh);
-	}
-}
-
 /*
  * Awaken the grace-period kthread.  Don't do a self-awaken (unless in an
  * interrupt or softirq handler, in which case we just might immediately
@@ -1116,7 +1084,7 @@ static void rcu_gp_kthread_wake(void)
 		return;
 	WRITE_ONCE(rcu_state.gp_wake_time, jiffies);
 	WRITE_ONCE(rcu_state.gp_wake_seq, READ_ONCE(rcu_state.gp_seq));
-	swake_up_one_online(&rcu_state.gp_wq);
+	swake_up_one(&rcu_state.gp_wq);
 }
 
 /*
diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 8d4895c854c5..c36c7d5575ca 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -200,7 +200,7 @@ static void __rcu_report_exp_rnp(struct rcu_node *rnp,
 		if (rnp->parent == NULL) {
 			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 			if (wake)
-				swake_up_one_online(&rcu_state.expedited_wq);
+				swake_up_one(&rcu_state.expedited_wq);
 
 			break;
 		}
diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
index fa269d34167a..109bc2df1d9a 100644
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -216,7 +216,7 @@ static bool __wake_nocb_gp(struct rcu_data *rdp_gp,
 	raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);
 	if (needwake) {
 		trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("DoWake"));
-		swake_up_one_online(&rdp_gp->nocb_gp_wq);
+		swake_up_one(&rdp_gp->nocb_gp_wq);
 	}
 
 	return needwake;
-- 
2.43.0