rcu: Shrink TINY_RCU by moving exit_rcu()

Now that TINY_PREEMPT_RCU is no more, exit_rcu() is always an empty
function.  But if TINY_RCU is going to have an empty function, it should
be in include/linux/rcutiny.h, where it does not bloat the kernel.
This commit therefore moves exit_rcu() out of kernel/rcupdate.c to
kernel/rcutree_plugin.h, and places a static inline empty function in
include/linux/rcutiny.h in order to shrink TINY_RCU a bit.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

5 files changed, 33 insertions, 27 deletions

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 257b50f9d2dc..4b14bdc911d7 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -240,8 +240,6 @@ static inline void rcu_user_hooks_switch(struct task_struct *prev,
                                          struct task_struct *next) { }
 #endif /* CONFIG_RCU_USER_QS */
 
-extern void exit_rcu(void);
-
 /**
  * RCU_NONIDLE - Indicate idle-loop code that needs RCU readers
  * @a: Code that RCU needs to pay attention to.
diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 51230b63be93..e31005ee339e 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -119,6 +119,10 @@ static inline void rcu_cpu_stall_reset(void)
 {
 }
 
+static inline void exit_rcu(void)
+{
+}
+
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 extern int rcu_scheduler_active __read_mostly;
 extern void rcu_scheduler_starting(void);
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 3f1aa8f98666..226169d1bd2b 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -85,6 +85,8 @@ extern void rcu_force_quiescent_state(void);
 extern void rcu_bh_force_quiescent_state(void);
 extern void rcu_sched_force_quiescent_state(void);
 
+extern void exit_rcu(void);
+
 extern void rcu_scheduler_starting(void);
 extern int rcu_scheduler_active __read_mostly;
 
diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index 48ab70384a4c..0be1fa2ea521 100644
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -104,31 +104,7 @@ void __rcu_read_unlock(void)
 }
 EXPORT_SYMBOL_GPL(__rcu_read_unlock);
 
-/*
- * Check for a task exiting while in a preemptible-RCU read-side
- * critical section, clean up if so.  No need to issue warnings,
- * as debug_check_no_locks_held() already does this if lockdep
- * is enabled.
- */
-void exit_rcu(void)
-{
-        struct task_struct *t = current;
-
-        if (likely(list_empty(&current->rcu_node_entry)))
-                return;
-        t->rcu_read_lock_nesting = 1;
-        barrier();
-        t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED;
-        __rcu_read_unlock();
-}
-
-#else /* #ifdef CONFIG_PREEMPT_RCU */
-
-void exit_rcu(void)
-{
-}
-
-#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
+#endif /* #ifdef CONFIG_PREEMPT_RCU */
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 static struct lock_class_key rcu_lock_key;
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 207844ea0226..de701bbdb624 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -932,6 +932,24 @@ static void __init __rcu_init_preempt(void)
         rcu_init_one(&rcu_preempt_state, &rcu_preempt_data);
 }
 
+/*
+ * Check for a task exiting while in a preemptible-RCU read-side
+ * critical section, clean up if so.  No need to issue warnings,
+ * as debug_check_no_locks_held() already does this if lockdep
+ * is enabled.
+ */
+void exit_rcu(void)
+{
+        struct task_struct *t = current;
+
+        if (likely(list_empty(&current->rcu_node_entry)))
+                return;
+        t->rcu_read_lock_nesting = 1;
+        barrier();
+        t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED;
+        __rcu_read_unlock();
+}
+
 #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
 
 static struct rcu_state *rcu_state = &rcu_sched_state;
@@ -1100,6 +1118,14 @@ static void __init __rcu_init_preempt(void)
 {
 }
 
+/*
+ * Because preemptible RCU does not exist, tasks cannot possibly exit
+ * while in preemptible RCU read-side critical sections.
+ */
+void exit_rcu(void)
+{
+}
+
 #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
 
 #ifdef CONFIG_RCU_BOOST