linux-kernel - [PATCH rcu 3/5] rcu: Assume rcu

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Date:   Mon, 18 Apr 2022 15:56:40 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com,
        rostedt@...dmis.org, Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Uladzislau Rezki <uladzislau.rezki@...y.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Boqun Feng <boqun.feng@...il.com>,
        "Paul E . McKenney" <paulmck@...nel.org>
Subject: [PATCH rcu 3/5] rcu: Assume rcu_init() is called before smp

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

The rcu_init() function is called way before SMP is initialized and
therefore only the boot CPU should be online at this stage.

Simplify the boot per-cpu initialization accordingly.

Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
Cc: Neeraj Upadhyay <quic_neeraju@...cinc.com>
Cc: Uladzislau Rezki <uladzislau.rezki@...y.com>
Cc: Joel Fernandes <joel@...lfernandes.org>
Cc: Boqun Feng <boqun.feng@...il.com>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 kernel/rcu/tree.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index a4b8189455d5..e6a9e5744e45 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -4782,7 +4782,7 @@ static void __init kfree_rcu_batch_init(void)
 
 void __init rcu_init(void)
 {
-	int cpu;
+	int cpu = smp_processor_id();
 
 	rcu_early_boot_tests();
 
@@ -4802,11 +4802,10 @@ void __init rcu_init(void)
 	 * or the scheduler are operational.
 	 */
 	pm_notifier(rcu_pm_notify, 0);
-	for_each_online_cpu(cpu) {
-		rcutree_prepare_cpu(cpu);
-		rcu_cpu_starting(cpu);
-		rcutree_online_cpu(cpu);
-	}
+	WARN_ON(num_online_cpus() > 1); // Only one CPU this early in boot.
+	rcutree_prepare_cpu(cpu);
+	rcu_cpu_starting(cpu);
+	rcutree_online_cpu(cpu);
 
 	/* Create workqueue for Tree SRCU and for expedited GPs. */
 	rcu_gp_wq = alloc_workqueue("rcu_gp", WQ_MEM_RECLAIM, 0);
-- 
2.31.1.189.g2e36527f23