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>

1 files changed, 5 insertions, 12 deletions

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);