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Message-ID: <20090710004828.GA19385@linux.vnet.ibm.com>
Date: Thu, 9 Jul 2009 17:48:28 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: linux-kernel@...r.kernel.org
Cc: mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com
Subject: [PATCH -tip] Simplify RCU CPU-hotplug notification
Simplify RCU's CPU-hotplug notifiers so that there is only one notifier.
This makes it trivial to provide the ordering guarantee that rcu_barrier()
depends on. This change also allows rcu_barrier() to rely on locking
wholly contained in _cpu_down(), rather than that of its callers, making
the locking more straightforward.
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
rcupdate.c | 8 ++++++--
rcupreempt.c | 22 +++++-----------------
rcutree.c | 18 +++++++++---------
3 files changed, 20 insertions(+), 28 deletions(-)
diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index eae29c2..3fea910 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(),
@@ -234,7 +238,7 @@ static int __cpuinit rcu_barrier_cpu_hotplug(struct notifier_block *self,
call_rcu_bh(rcu_migrate_head, rcu_migrate_callback);
call_rcu_sched(rcu_migrate_head + 1, rcu_migrate_callback);
call_rcu(rcu_migrate_head + 2, rcu_migrate_callback);
- } else if (action == CPU_POST_DEAD) {
+ } else if (action == CPU_DEAD) {
/* rcu_migrate_head is protected by cpu_add_remove_lock */
wait_migrated_callbacks();
}
@@ -244,8 +248,8 @@ static int __cpuinit rcu_barrier_cpu_hotplug(struct notifier_block *self,
void __init rcu_init(void)
{
- __rcu_init();
hotcpu_notifier(rcu_barrier_cpu_hotplug, 0);
+ __rcu_init();
}
void rcu_scheduler_starting(void)
diff --git a/kernel/rcupreempt.c b/kernel/rcupreempt.c
index beb0e65..4300212 100644
--- a/kernel/rcupreempt.c
+++ b/kernel/rcupreempt.c
@@ -1417,7 +1417,7 @@ int rcu_pending(int cpu)
return 0;
}
-static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
+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;
@@ -1471,22 +1467,14 @@ 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.
+ * 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(cpu)
- rcu_cpu_notify(&rcu_nb, CPU_UP_PREPARE, (void *)(long) cpu);
+ rcu_cpu_notify(NULL, CPU_UP_PREPARE, (void *)(long) cpu);
open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
}
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 7717b95..e8e9e93 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1407,13 +1407,12 @@ 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,
+int __cpuinit rcu_cpu_notify(struct notifier_block *self,
unsigned long action, void *hcpu)
{
long cpu = (long)hcpu;
@@ -1523,10 +1522,6 @@ 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(). */
@@ -1542,10 +1537,15 @@ void __init __rcu_init(void)
rcu_init_one(&rcu_bh_state);
RCU_DATA_PTR_INIT(&rcu_bh_state, rcu_bh_data);
+ /*
+ * 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_cpu_notify(&rcu_nb, CPU_UP_PREPARE, (void *)(long)i);
- /* Register notifier for non-boot CPUs */
- register_cpu_notifier(&rcu_nb);
+ rcu_cpu_notify(NULL, CPU_UP_PREPARE, (void *)(long)i);
+
+ open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
}
module_param(blimit, int, 0);
--
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