[PATCH -tip 2/2] Add CPU-offline processing for single-node configurations

[Paul E. McKenney]

From: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>

Add preemptable-RCU plugin to handle the CPU-offline processing.
An additional plugin is forthcoming to handle multinode RCU trees, but
this current plugin works for configurations up to 32 CPUs (64 CPUs for
64-bit kernels).

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
 kernel/rcutree.c        |    2 ++
 kernel/rcutree_plugin.h |   24 ++++++++++++++++++++++++
 2 files changed, 26 insertions(+), 0 deletions(-)

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index cc02557..000b076 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -84,6 +84,7 @@ extern long rcu_batches_completed_sched(void);
 static void cpu_quiet_msk(unsigned long mask, struct rcu_state *rsp,
 			  struct rcu_node *rnp, unsigned long flags);
 static void cpu_quiet_msk_finish(struct rcu_state *rsp, unsigned long flags);
+static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp);
 static void __rcu_process_callbacks(struct rcu_state *rsp,
 				    struct rcu_data *rdp);
 static void __call_rcu(struct rcu_head *head,
@@ -920,6 +921,7 @@ static void rcu_offline_cpu(int cpu)
 {
 	__rcu_offline_cpu(cpu, &rcu_sched_state);
 	__rcu_offline_cpu(cpu, &rcu_bh_state);
+	rcu_preempt_offline_cpu(cpu);
 }
 
 #else /* #ifdef CONFIG_HOTPLUG_CPU */
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index cd2ab67..201334c 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -259,6 +259,18 @@ static int rcu_preempted_readers(struct rcu_node *rnp)
 	return !list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1]);
 }
 
+#ifdef CONFIG_HOTPLUG_CPU
+
+/*
+ * Do CPU-offline processing for preemptable RCU.
+ */
+static void rcu_preempt_offline_cpu(int cpu)
+{
+	__rcu_offline_cpu(cpu, &rcu_preempt_state);
+}
+
+#endif /* #ifdef CONFIG_HOTPLUG_CPU */
+
 /*
  * Check for a quiescent state from the current CPU.  When a task blocks,
  * the task is recorded in the corresponding CPU's rcu_node structure,
@@ -395,6 +407,18 @@ static int rcu_preempted_readers(struct rcu_node *rnp)
 	return 0;
 }
 
+#ifdef CONFIG_HOTPLUG_CPU
+
+/*
+ * Because preemptable RCU does not exist, it never needs CPU-offline
+ * processing.
+ */
+static void rcu_preempt_offline_cpu(int cpu)
+{
+}
+
+#endif /* #ifdef CONFIG_HOTPLUG_CPU */
+
 /*
  * Because preemptable RCU does not exist, it never has any callbacks
  * to check.
-- 
1.5.2.5

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