sched: Allow hotplug notifiers to be setup early

Prevent the SMP scheduler related notifiers to be executed before the smp
scheduler is initialized and install them early.

This is a preparatory change for further consolidation of the hotplug notifier
maze.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: rt@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 36 insertions, 23 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 4df9aaae27a2..328502c9af00 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5195,6 +5195,8 @@ out:
 
 #ifdef CONFIG_SMP
 
+static bool sched_smp_initialized __read_mostly;
+
 #ifdef CONFIG_NUMA_BALANCING
 /* Migrate current task p to target_cpu */
 int migrate_task_to(struct task_struct *p, int target_cpu)
@@ -5513,25 +5515,6 @@ int sched_cpu_starting(unsigned int cpu)
         return 0;
 }
 
-static int __init migration_init(void)
-{
-        void *cpu = (void *)(long)smp_processor_id();
-        int err;
-
-        /* Initialize migration for the boot CPU */
-        err = migration_call(&migration_notifier, CPU_UP_PREPARE, cpu);
-        BUG_ON(err == NOTIFY_BAD);
-        migration_call(&migration_notifier, CPU_ONLINE, cpu);
-        register_cpu_notifier(&migration_notifier);
-
-        /* Register cpu active notifiers */
-        cpu_notifier(sched_cpu_active, CPU_PRI_SCHED_ACTIVE);
-        cpu_notifier(sched_cpu_inactive, CPU_PRI_SCHED_INACTIVE);
-
-        return 0;
-}
-early_initcall(migration_init);
-
 static cpumask_var_t sched_domains_tmpmask; /* sched_domains_mutex */
 
 #ifdef CONFIG_SCHED_DEBUG
@@ -6711,6 +6694,9 @@ static int sched_domains_numa_masks_update(struct notifier_block *nfb,
 {
         int cpu = (long)hcpu;
 
+        if (!sched_smp_initialized)
+                return NOTIFY_DONE;
+
         switch (action & ~CPU_TASKS_FROZEN) {
         case CPU_ONLINE:
                 sched_domains_numa_masks_set(cpu);
@@ -7129,6 +7115,9 @@ static int num_cpus_frozen;	/* used to mark begin/end of suspend/resume */
 static int cpuset_cpu_active(struct notifier_block *nfb, unsigned long action,
                              void *hcpu)
 {
+        if (!sched_smp_initialized)
+                return NOTIFY_DONE;
+
         switch (action) {
         case CPU_ONLINE_FROZEN:
         case CPU_DOWN_FAILED_FROZEN:
@@ -7169,6 +7158,9 @@ static int cpuset_cpu_inactive(struct notifier_block *nfb, unsigned long action,
         bool overflow;
         int cpus;
 
+        if (!sched_smp_initialized)
+                return NOTIFY_DONE;
+
         switch (action) {
         case CPU_DOWN_PREPARE:
                 rcu_read_lock_sched();
@@ -7216,10 +7208,6 @@ void __init sched_init_smp(void)
                 cpumask_set_cpu(smp_processor_id(), non_isolated_cpus);
         mutex_unlock(&sched_domains_mutex);
 
-        hotcpu_notifier(sched_domains_numa_masks_update, CPU_PRI_SCHED_ACTIVE);
-        hotcpu_notifier(cpuset_cpu_active, CPU_PRI_CPUSET_ACTIVE);
-        hotcpu_notifier(cpuset_cpu_inactive, CPU_PRI_CPUSET_INACTIVE);
-
         init_hrtick();
 
         /* Move init over to a non-isolated CPU */
@@ -7230,7 +7218,32 @@ void __init sched_init_smp(void)
 
         init_sched_rt_class();
         init_sched_dl_class();
+        sched_smp_initialized = true;
 }
+
+static int __init migration_init(void)
+{
+        void *cpu = (void *)(long)smp_processor_id();
+        int err;
+
+        /* Initialize migration for the boot CPU */
+        err = migration_call(&migration_notifier, CPU_UP_PREPARE, cpu);
+        BUG_ON(err == NOTIFY_BAD);
+        migration_call(&migration_notifier, CPU_ONLINE, cpu);
+        register_cpu_notifier(&migration_notifier);
+
+        /* Register cpu active notifiers */
+        cpu_notifier(sched_cpu_active, CPU_PRI_SCHED_ACTIVE);
+        cpu_notifier(sched_cpu_inactive, CPU_PRI_SCHED_INACTIVE);
+
+        hotcpu_notifier(sched_domains_numa_masks_update, CPU_PRI_SCHED_ACTIVE);
+        hotcpu_notifier(cpuset_cpu_active, CPU_PRI_CPUSET_ACTIVE);
+        hotcpu_notifier(cpuset_cpu_inactive, CPU_PRI_CPUSET_INACTIVE);
+
+        return 0;
+}
+early_initcall(migration_init);
+
 #else
 void __init sched_init_smp(void)
 {