[PATCH -tip/core/rcu 3/6] Simplify RCU CPU-hotplug notification

Paul E. McKenney
2009-08-15T16:54:18Z

From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

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>
---
kernel/rcupdate.c | 16 +++++++++++++++-
kernel/rcupreempt.c | 25 ++-----------------------
kernel/rcutree.c | 17 +++++------------
3 files changed, 22 insertions(+), 36 deletions(-)

diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index eae29c2..8df1156 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 beb0e65..9b87f51 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 f3e4327..75762cd 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);
--
1.5.2.5