rcu: Simplify RCU CPU-hotplug notification

Use the new cpu_notifier() API to simplify RCU's CPU-hotplug
notifiers, collapsing down to a single such notifier.

This makes it trivial to provide the notifier-ordering
guarantee that rcu_barrier() depends on.

Also remove redundant open_softirq() calls from Hierarchical
RCU notifier.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: josht@linux.vnet.ibm.com
Cc: akpm@linux-foundation.org
Cc: mathieu.desnoyers@polymtl.ca
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: hugh.dickins@tiscali.co.uk
Cc: benh@kernel.crashing.org
LKML-Reference: <12503552312510-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>

3 files changed, 22 insertions, 36 deletions

diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index eae29c25fb14..8df115600c2d 100644
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -217,9 +217,13 @@ static void rcu_migrate_callback(struct rcu_head *notused)
                 wake_up(&rcu_migrate_wq);
 }
 
+extern int rcu_cpu_notify(struct notifier_block *self,
+                          unsigned long action, void *hcpu);
+
 static int __cpuinit rcu_barrier_cpu_hotplug(struct notifier_block *self,
                 unsigned long action, void *hcpu)
 {
+        rcu_cpu_notify(self, action, hcpu);
         if (action == CPU_DYING) {
                 /*
                  * preempt_disable() in on_each_cpu() prevents stop_machine(),
@@ -244,8 +248,18 @@ static int __cpuinit rcu_barrier_cpu_hotplug(struct notifier_block *self,
 
 void __init rcu_init(void)
 {
+        int i;
+
         __rcu_init();
-        hotcpu_notifier(rcu_barrier_cpu_hotplug, 0);
+        cpu_notifier(rcu_barrier_cpu_hotplug, 0);
+
+        /*
+         * We don't need protection against CPU-hotplug here because
+         * this is called early in boot, before either interrupts
+         * or the scheduler are operational.
+         */
+        for_each_online_cpu(i)
+                rcu_barrier_cpu_hotplug(NULL, CPU_UP_PREPARE, (void *)(long)i);
 }
 
 void rcu_scheduler_starting(void)
diff --git a/kernel/rcupreempt.c b/kernel/rcupreempt.c
index beb0e659adcc..9b87f5134ed7 100644
--- a/kernel/rcupreempt.c
+++ b/kernel/rcupreempt.c
@@ -1417,8 +1417,8 @@ int rcu_pending(int cpu)
         return 0;
 }
 
-static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
-                                unsigned long action, void *hcpu)
+int __cpuinit rcu_cpu_notify(struct notifier_block *self,
+                             unsigned long action, void *hcpu)
 {
         long cpu = (long)hcpu;
 
@@ -1439,10 +1439,6 @@ static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
         return NOTIFY_OK;
 }
 
-static struct notifier_block __cpuinitdata rcu_nb = {
-        .notifier_call = rcu_cpu_notify,
-};
-
 void __init __rcu_init(void)
 {
         int cpu;
@@ -1471,23 +1467,6 @@ void __init __rcu_init(void)
                 rdp->waitschedtail = &rdp->waitschedlist;
                 rdp->rcu_sched_sleeping = 0;
         }
-        register_cpu_notifier(&rcu_nb);
-
-        /*
-         * We don't need protection against CPU-Hotplug here
-         * since
-         * a) If a CPU comes online while we are iterating over the
-         *    cpu_online_mask below, we would only end up making a
-         *    duplicate call to rcu_online_cpu() which sets the corresponding
-         *    CPU's mask in the rcu_cpu_online_map.
-         *
-         * b) A CPU cannot go offline at this point in time since the user
-         *    does not have access to the sysfs interface, nor do we
-         *    suspend the system.
-         */
-        for_each_online_cpu(cpu)
-                rcu_cpu_notify(&rcu_nb, CPU_UP_PREPARE, (void *)(long) cpu);
-
         open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
 }
 
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index f3e43274ed53..75762cddbe03 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1132,6 +1132,8 @@ __rcu_process_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
 {
         unsigned long flags;
 
+        WARN_ON_ONCE(rdp->beenonline == 0);
+
         /*
          * If an RCU GP has gone long enough, go check for dyntick
          * idle CPUs and, if needed, send resched IPIs.
@@ -1416,14 +1418,13 @@ static void __cpuinit rcu_online_cpu(int cpu)
 {
         rcu_init_percpu_data(cpu, &rcu_state);
         rcu_init_percpu_data(cpu, &rcu_bh_state);
-        open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
 }
 
 /*
  * Handle CPU online/offline notifcation events.
  */
-static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
-                                unsigned long action, void *hcpu)
+int __cpuinit rcu_cpu_notify(struct notifier_block *self,
+                             unsigned long action, void *hcpu)
 {
         long cpu = (long)hcpu;
 
@@ -1532,10 +1533,6 @@ do { \
         } \
 } while (0)
 
-static struct notifier_block __cpuinitdata rcu_nb = {
-        .notifier_call  = rcu_cpu_notify,
-};
-
 void __init __rcu_init(void)
 {
         int i;                  /* All used by RCU_DATA_PTR_INIT(). */
@@ -1554,11 +1551,7 @@ void __init __rcu_init(void)
         RCU_DATA_PTR_INIT(&rcu_bh_state, rcu_bh_data);
         for_each_possible_cpu(i)
                 rcu_boot_init_percpu_data(i, &rcu_bh_state);
-
-        for_each_online_cpu(i)
-                rcu_cpu_notify(&rcu_nb, CPU_UP_PREPARE, (void *)(long)i);
-        /* Register notifier for non-boot CPUs */
-        register_cpu_notifier(&rcu_nb);
+        open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
 }
 
 module_param(blimit, int, 0);