[patch 32/40] rcu: Convert rcutree to hotplug state machine

[Thomas Gleixner]

Do we really need so many states here ?

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
 include/linux/cpuhotplug.h |   18 ++++++++
 kernel/cpu.c               |   12 +++++
 kernel/rcutree.c           |   95 ++++++++++++++++++++-------------------------
 3 files changed, 73 insertions(+), 52 deletions(-)

Index: linux-2.6/include/linux/cpuhotplug.h
===================================================================
--- linux-2.6.orig/include/linux/cpuhotplug.h
+++ linux-2.6/include/linux/cpuhotplug.h
@@ -12,6 +12,7 @@ enum cpuhp_states {
 	CPUHP_PERF_PREPARE,
 	CPUHP_SCHED_MIGRATE_PREP,
 	CPUHP_WORKQUEUE_PREP,
+	CPUHP_RCUTREE_PREPARE,
 	CPUHP_NOTIFY_PREPARE,
 	CPUHP_NOTIFY_DEAD,
 	CPUHP_CPUFREQ_DEAD,
@@ -27,6 +28,7 @@ enum cpuhp_states {
 	CPUHP_AP_ARM64_TIMER_STARTING,
 	CPUHP_AP_KVM_STARTING,
 	CPUHP_AP_NOTIFY_DYING,
+	CPUHP_AP_RCUTREE_DYING,
 	CPUHP_AP_X86_TBOOT_DYING,
 	CPUHP_AP_S390_VTIME_DYING,
 	CPUHP_AP_SCHED_NOHZ_DYING,
@@ -39,6 +41,7 @@ enum cpuhp_states {
 	CPUHP_SCHED_MIGRATE_ONLINE,
 	CPUHP_WORKQUEUE_ONLINE,
 	CPUHP_CPUFREQ_ONLINE,
+	CPUHP_RCUTREE_ONLINE,
 	CPUHP_NOTIFY_ONLINE,
 	CPUHP_NOTIFY_DOWN_PREPARE,
 	CPUHP_PERF_X86_UNCORE_ONLINE,
@@ -147,4 +150,19 @@ int workqueue_prepare_cpu(unsigned int c
 int workqueue_online_cpu(unsigned int cpu);
 int workqueue_offline_cpu(unsigned int cpu);
 
+/* RCUtree hotplug events */
+#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
+int rcutree_prepare_cpu(unsigned int cpu);
+int rcutree_online_cpu(unsigned int cpu);
+int rcutree_offline_cpu(unsigned int cpu);
+int rcutree_dead_cpu(unsigned int cpu);
+int rcutree_dying_cpu(unsigned int cpu);
+#else
+#define rcutree_prepare_cpu	NULL
+#define rcutree_online_cpu	NULL
+#define rcutree_offline_cpu	NULL
+#define rcutree_dead_cpu	NULL
+#define rcutree_dying_cpu	NULL
+#endif
+
 #endif
Index: linux-2.6/kernel/cpu.c
===================================================================
--- linux-2.6.orig/kernel/cpu.c
+++ linux-2.6/kernel/cpu.c
@@ -755,6 +755,10 @@ static struct cpuhp_step cpuhp_bp_states
 		.startup = workqueue_prepare_cpu,
 		.teardown = NULL,
 	},
+	[CPUHP_RCUTREE_PREPARE] = {
+		.startup = rcutree_prepare_cpu,
+		.teardown = rcutree_dead_cpu,
+	},
 	[CPUHP_NOTIFY_PREPARE] = {
 		.startup = notify_prepare,
 		.teardown = NULL,
@@ -787,6 +791,10 @@ static struct cpuhp_step cpuhp_bp_states
 		.startup = workqueue_online_cpu,
 		.teardown = workqueue_offline_cpu,
 	},
+	[CPUHP_RCUTREE_ONLINE] = {
+		.startup = rcutree_online_cpu,
+		.teardown = rcutree_offline_cpu,
+	},
 	[CPUHP_NOTIFY_ONLINE] = {
 		.startup = notify_online,
 		.teardown = NULL,
@@ -813,6 +821,10 @@ static struct cpuhp_step cpuhp_ap_states
 		.startup = NULL,
 		.teardown = notify_dying,
 	},
+	[CPUHP_AP_RCUTREE_DYING] = {
+		.startup = NULL,
+		.teardown = rcutree_dying_cpu,
+	},
 	[CPUHP_AP_SCHED_NOHZ_DYING] = {
 		.startup = NULL,
 		.teardown = nohz_balance_exit_idle,
Index: linux-2.6/kernel/rcutree.c
===================================================================
--- linux-2.6.orig/kernel/rcutree.c
+++ linux-2.6/kernel/rcutree.c
@@ -2787,67 +2787,59 @@ rcu_init_percpu_data(int cpu, struct rcu
 	mutex_unlock(&rsp->onoff_mutex);
 }
 
-static void __cpuinit rcu_prepare_cpu(int cpu)
+int __cpuinit rcutree_prepare_cpu(unsigned int cpu)
 {
 	struct rcu_state *rsp;
 
 	for_each_rcu_flavor(rsp)
 		rcu_init_percpu_data(cpu, rsp,
 				     strcmp(rsp->name, "rcu_preempt") == 0);
+	rcu_prepare_kthreads(cpu);
+	return 0;
 }
 
-/*
- * Handle CPU online/offline notification events.
- */
-static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
-				    unsigned long action, void *hcpu)
+int __cpuinit rcutree_dead_cpu(unsigned int cpu)
 {
-	long cpu = (long)hcpu;
-	struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
-	struct rcu_node *rnp = rdp->mynode;
 	struct rcu_state *rsp;
-	int ret = NOTIFY_OK;
 
-	trace_rcu_utilization("Start CPU hotplug");
-	switch (action) {
-	case CPU_UP_PREPARE:
-	case CPU_UP_PREPARE_FROZEN:
-		rcu_prepare_cpu(cpu);
-		rcu_prepare_kthreads(cpu);
-		break;
-	case CPU_ONLINE:
-	case CPU_DOWN_FAILED:
-		rcu_boost_kthread_setaffinity(rnp, -1);
-		break;
-	case CPU_DOWN_PREPARE:
-		if (nocb_cpu_expendable(cpu))
-			rcu_boost_kthread_setaffinity(rnp, cpu);
-		else
-			ret = NOTIFY_BAD;
-		break;
-	case CPU_DYING:
-	case CPU_DYING_FROZEN:
-		/*
-		 * The whole machine is "stopped" except this CPU, so we can
-		 * touch any data without introducing corruption. We send the
-		 * dying CPU's callbacks to an arbitrarily chosen online CPU.
-		 */
-		for_each_rcu_flavor(rsp)
-			rcu_cleanup_dying_cpu(rsp);
-		rcu_cleanup_after_idle(cpu);
-		break;
-	case CPU_DEAD:
-	case CPU_DEAD_FROZEN:
-	case CPU_UP_CANCELED:
-	case CPU_UP_CANCELED_FROZEN:
-		for_each_rcu_flavor(rsp)
-			rcu_cleanup_dead_cpu(cpu, rsp);
-		break;
-	default:
-		break;
-	}
-	trace_rcu_utilization("End CPU hotplug");
-	return ret;
+	for_each_rcu_flavor(rsp)
+		rcu_cleanup_dead_cpu(cpu, rsp);
+	return 0;
+}
+
+static void __cpuinit rcutree_affinity_setting(unsigned int cpu, int outgoing)
+{
+	struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
+
+	rcu_boost_kthread_setaffinity(rdp->mynode, outgoing);
+}
+
+int __cpuinit rcutree_online_cpu(unsigned int cpu)
+{
+	rcutree_affinity_setting(cpu, -1);
+	return 0;
+}
+
+int __cpuinit rcutree_offline_cpu(unsigned int cpu)
+{
+	if (!nocb_cpu_expendable(cpu))
+		return -EINVAL;
+	rcutree_affinity_setting(cpu, cpu);
+	return 0;
+}
+
+int __cpuinit rcutree_dying_cpu(unsigned int cpu)
+{
+	struct rcu_state *rsp;
+	/*
+	 * The whole machine is "stopped" except this CPU, so we can
+	 * touch any data without introducing corruption. We send the
+	 * dying CPU's callbacks to an arbitrarily chosen online CPU.
+	 */
+	for_each_rcu_flavor(rsp)
+		rcu_cleanup_dying_cpu(rsp);
+	rcu_cleanup_after_idle(cpu);
+	return 0;
 }
 
 /*
@@ -3071,9 +3063,8 @@ void __init rcu_init(void)
 	 * this is called early in boot, before either interrupts
 	 * or the scheduler are operational.
 	 */
-	cpu_notifier(rcu_cpu_notify, 0);
 	for_each_online_cpu(cpu)
-		rcu_cpu_notify(NULL, CPU_UP_PREPARE, (void *)(long)cpu);
+		rcutree_prepare_cpu(cpu);
 	check_cpu_stall_init();
 }
 


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