rcu: Replace the rcu_barrier enum with pointer to call_rcu*() function

The rcu_barrier enum causes several problems:

  (1) you have to define the enum somewhere, and there is no
      convenient place,

  (2) the difference between TREE_RCU and TREE_PREEMPT_RCU causes
      problems when you need to map from rcu_barrier enum to struct
      rcu_state,

  (3) the switch statement are large, and

  (4) TINY_RCU really needs a different rcu_barrier() than do the
      treercu implementations.

So replace it with a functionally equivalent but cleaner function
pointer abstraction.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: akpm@linux-foundation.org
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <12541998232366-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/rcupdate.c

@@ -53,12 +53,6 @@ struct lockdep_map rcu_lock_map =
 EXPORT_SYMBOL_GPL(rcu_lock_map);
 #endif
 
-enum rcu_barrier {
-	RCU_BARRIER_STD,
-	RCU_BARRIER_BH,
-	RCU_BARRIER_SCHED,
-};
-
 static DEFINE_PER_CPU(struct rcu_head, rcu_barrier_head) = {NULL};
 static atomic_t rcu_barrier_cpu_count;
 static DEFINE_MUTEX(rcu_barrier_mutex);
@@ -184,19 +178,12 @@ static void rcu_barrier_func(void *type)
 {
 	int cpu = smp_processor_id();
 	struct rcu_head *head = &per_cpu(rcu_barrier_head, cpu);
+	void (*call_rcu_func)(struct rcu_head *head,
+			      void (*func)(struct rcu_head *head));
 
 	atomic_inc(&rcu_barrier_cpu_count);
-	switch ((enum rcu_barrier)type) {
-	case RCU_BARRIER_STD:
-		call_rcu(head, rcu_barrier_callback);
-		break;
-	case RCU_BARRIER_BH:
-		call_rcu_bh(head, rcu_barrier_callback);
-		break;
-	case RCU_BARRIER_SCHED:
-		call_rcu_sched(head, rcu_barrier_callback);
-		break;
-	}
+	call_rcu_func = type;
+	call_rcu_func(head, rcu_barrier_callback);
 }
 
 static inline void wait_migrated_callbacks(void)
@@ -209,7 +196,8 @@ static inline void wait_migrated_callbacks(void)
  * Orchestrate the specified type of RCU barrier, waiting for all
  * RCU callbacks of the specified type to complete.
  */
-static void _rcu_barrier(enum rcu_barrier type)
+static void _rcu_barrier(void (*call_rcu_func)(struct rcu_head *head,
+					       void (*func)(struct rcu_head *head)))
 {
 	BUG_ON(in_interrupt());
 	/* Take cpucontrol mutex to protect against CPU hotplug */
@@ -225,7 +213,7 @@ static void _rcu_barrier(enum rcu_barrier type)
 	 * early.
 	 */
 	atomic_set(&rcu_barrier_cpu_count, 1);
-	on_each_cpu(rcu_barrier_func, (void *)type, 1);
+	on_each_cpu(rcu_barrier_func, (void *)call_rcu_func, 1);
 	if (atomic_dec_and_test(&rcu_barrier_cpu_count))
 		complete(&rcu_barrier_completion);
 	wait_for_completion(&rcu_barrier_completion);
@@ -238,7 +226,7 @@ static void _rcu_barrier(enum rcu_barrier type)
  */
 void rcu_barrier(void)
 {
-	_rcu_barrier(RCU_BARRIER_STD);
+	_rcu_barrier(call_rcu);
 }
 EXPORT_SYMBOL_GPL(rcu_barrier);
 
@@ -247,7 +235,7 @@ EXPORT_SYMBOL_GPL(rcu_barrier);
  */
 void rcu_barrier_bh(void)
 {
-	_rcu_barrier(RCU_BARRIER_BH);
+	_rcu_barrier(call_rcu_bh);
 }
 EXPORT_SYMBOL_GPL(rcu_barrier_bh);
 
@@ -256,7 +244,7 @@ EXPORT_SYMBOL_GPL(rcu_barrier_bh);
  */
 void rcu_barrier_sched(void)
 {
-	_rcu_barrier(RCU_BARRIER_SCHED);
+	_rcu_barrier(call_rcu_sched);
 }
 EXPORT_SYMBOL_GPL(rcu_barrier_sched);