rcu: Initialize boost kthread only for boot node prior SMP initializa…

…tion The rcu_spawn_gp_kthread() function is called as an early initcall, which means that SMP initialization hasn't happened yet and only the boot CPU is online. Therefore, create only the boost kthread for the leaf node of the boot CPU. Signed-off-by: Frederic Weisbecker <[email protected]> Cc: Neeraj Upadhyay <[email protected]> Cc: Uladzislau Rezki <[email protected]> Cc: Joel Fernandes <[email protected]> Cc: Boqun Feng <[email protected]> Signed-off-by: Paul E. McKenney <[email protected]>
ambv · Apr 12, 2022 · 3352911 · 3352911
1 parent 2eed973
commit 3352911
Show file tree

Hide file tree

Showing 3 changed files with 4 additions and 18 deletions.
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
@@ -4480,6 +4480,7 @@ static int __init rcu_spawn_gp_kthread(void)
 	struct rcu_node *rnp;
 	struct sched_param sp;
 	struct task_struct *t;
+	struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
 
 	rcu_scheduler_fully_active = 1;
 	t = kthread_create(rcu_gp_kthread, NULL, "%s", rcu_state.name);
@@ -4498,7 +4499,9 @@ static int __init rcu_spawn_gp_kthread(void)
 	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 	wake_up_process(t);
 	rcu_spawn_nocb_kthreads();
-	rcu_spawn_boost_kthreads();
+	/* This is a pre-SMP initcall, we expect a single CPU */
+	WARN_ON(num_online_cpus() > 1);
+	rcu_spawn_one_boost_kthread(rdp->mynode);
 	rcu_spawn_core_kthreads();
 	return 0;
 }

diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
@@ -422,7 +422,6 @@ static void rcu_preempt_boost_start_gp(struct rcu_node *rnp);
 static bool rcu_is_callbacks_kthread(void);
 static void rcu_cpu_kthread_setup(unsigned int cpu);
 static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp);
-static void __init rcu_spawn_boost_kthreads(void);
 static bool rcu_preempt_has_tasks(struct rcu_node *rnp);
 static bool rcu_preempt_need_deferred_qs(struct task_struct *t);
 static void rcu_preempt_deferred_qs(struct task_struct *t);

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
@@ -1226,18 +1226,6 @@ static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
 	free_cpumask_var(cm);
 }
 
-/*
- * Spawn boost kthreads -- called as soon as the scheduler is running.
- */
-static void __init rcu_spawn_boost_kthreads(void)
-{
-	struct rcu_node *rnp;
-
-	rcu_for_each_leaf_node(rnp)
-		if (rcu_rnp_online_cpus(rnp))
-			rcu_spawn_one_boost_kthread(rnp);
-}
-
 #else /* #ifdef CONFIG_RCU_BOOST */
 
 static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
@@ -1263,10 +1251,6 @@ static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
 {
 }
 
-static void __init rcu_spawn_boost_kthreads(void)
-{
-}
-
 #endif /* #else #ifdef CONFIG_RCU_BOOST */
 
 /*