rcu: Rationalize kthread spawning

Currently, RCU spawns kthreads from several different early_initcall()
functions.  Although this has served RCU well for quite some time,
as more kthreads are added a more deterministic approach is required.
This commit therefore causes all of RCU's early-boot kthreads to be
spawned from a single early_initcall() function.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Tested-by: Paul Gortmaker <paul.gortmaker@windriver.com>

3 files changed, 7 insertions, 10 deletions

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 1b70cb6fbe3c..9be47f43903b 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3489,7 +3489,7 @@ static int rcu_pm_notify(struct notifier_block *self,
 }
 
 /*
- * Spawn the kthread that handles this RCU flavor's grace periods.
+ * Spawn the kthreads that handle each RCU flavor's grace periods.
  */
 static int __init rcu_spawn_gp_kthread(void)
 {
@@ -3498,6 +3498,7 @@ static int __init rcu_spawn_gp_kthread(void)
         struct rcu_state *rsp;
         struct task_struct *t;
 
+        rcu_scheduler_fully_active = 1;
         for_each_rcu_flavor(rsp) {
                 t = kthread_run(rcu_gp_kthread, rsp, "%s", rsp->name);
                 BUG_ON(IS_ERR(t));
@@ -3507,6 +3508,7 @@ static int __init rcu_spawn_gp_kthread(void)
                 raw_spin_unlock_irqrestore(&rnp->lock, flags);
                 rcu_spawn_nocb_kthreads(rsp);
         }
+        rcu_spawn_boost_kthreads();
         return 0;
 }
 early_initcall(rcu_spawn_gp_kthread);
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 6a86eb7bac45..a966092fdfd7 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -572,6 +572,7 @@ static void rcu_preempt_do_callbacks(void);
 static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
                                                  struct rcu_node *rnp);
 #endif /* #ifdef CONFIG_RCU_BOOST */
+static void __init rcu_spawn_boost_kthreads(void);
 static void rcu_prepare_kthreads(int cpu);
 static void rcu_cleanup_after_idle(int cpu);
 static void rcu_prepare_for_idle(int cpu);
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 4c1af96836f6..410c74424d96 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1435,14 +1435,13 @@ static struct smp_hotplug_thread rcu_cpu_thread_spec = {
 };
 
 /*
- * Spawn all kthreads -- called as soon as the scheduler is running.
+ * Spawn boost kthreads -- called as soon as the scheduler is running.
  */
-static int __init rcu_spawn_kthreads(void)
+static void __init rcu_spawn_boost_kthreads(void)
 {
         struct rcu_node *rnp;
         int cpu;
 
-        rcu_scheduler_fully_active = 1;
         for_each_possible_cpu(cpu)
                 per_cpu(rcu_cpu_has_work, cpu) = 0;
         BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec));
@@ -1452,9 +1451,7 @@ static int __init rcu_spawn_kthreads(void)
                 rcu_for_each_leaf_node(rcu_state_p, rnp)
                         (void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
         }
-        return 0;
 }
-early_initcall(rcu_spawn_kthreads);
 
 static void rcu_prepare_kthreads(int cpu)
 {
@@ -1492,12 +1489,9 @@ static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
 {
 }
 
-static int __init rcu_scheduler_really_started(void)
+static void __init rcu_spawn_boost_kthreads(void)
 {
-        rcu_scheduler_fully_active = 1;
-        return 0;
 }
-early_initcall(rcu_scheduler_really_started);
 
 static void rcu_prepare_kthreads(int cpu)
 {