rcu: Simplify RCU_TINY RCU callback invocation

TINY_PREEMPT_RCU could use a kthread to handle RCU callback invocation,
which required an API to abstract kthread vs. softirq invocation.
Now that TINY_PREEMPT_RCU is no longer with us, this commit retires
this API in favor of direct use of the relevant softirq primitives.

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

2 files changed, 9 insertions, 38 deletions

diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c
index 7fc2339b0859..4adc9e26da34 100644
--- a/kernel/rcutiny.c
+++ b/kernel/rcutiny.c
@@ -44,7 +44,6 @@
 
 /* Forward declarations for rcutiny_plugin.h. */
 struct rcu_ctrlblk;
-static void invoke_rcu_callbacks(void);
 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp);
 static void rcu_process_callbacks(struct softirq_action *unused);
 static void __call_rcu(struct rcu_head *head,
@@ -227,7 +226,7 @@ void rcu_sched_qs(int cpu)
         local_irq_save(flags);
         if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
             rcu_qsctr_help(&rcu_bh_ctrlblk))
-                invoke_rcu_callbacks();
+                raise_softirq(RCU_SOFTIRQ);
         local_irq_restore(flags);
 }
 
@@ -240,7 +239,7 @@ void rcu_bh_qs(int cpu)
 
         local_irq_save(flags);
         if (rcu_qsctr_help(&rcu_bh_ctrlblk))
-                invoke_rcu_callbacks();
+                raise_softirq(RCU_SOFTIRQ);
         local_irq_restore(flags);
 }
 
@@ -277,7 +276,7 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
                                               ACCESS_ONCE(rcp->rcucblist),
                                               need_resched(),
                                               is_idle_task(current),
-                                              rcu_is_callbacks_kthread()));
+                                              false));
                 return;
         }
 
@@ -307,7 +306,7 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
         RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));
         RCU_TRACE(trace_rcu_batch_end(rcp->name, cb_count, 0, need_resched(),
                                       is_idle_task(current),
-                                      rcu_is_callbacks_kthread()));
+                                      false));
 }
 
 static void rcu_process_callbacks(struct softirq_action *unused)
@@ -379,3 +378,8 @@ void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
         __call_rcu(head, func, &rcu_bh_ctrlblk);
 }
 EXPORT_SYMBOL_GPL(call_rcu_bh);
+
+void rcu_init(void)
+{
+        open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
+}
diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h
index bfe992407803..36fd83c544c8 100644
--- a/kernel/rcutiny_plugin.h
+++ b/kernel/rcutiny_plugin.h
@@ -102,39 +102,6 @@ static void check_cpu_stalls(void)
         RCU_TRACE(check_cpu_stall_preempt());
 }
 
-/* Hold off callback invocation until early_initcall() time. */
-static int rcu_scheduler_fully_active __read_mostly;
-
-/*
- * Start up softirq processing of callbacks.
- */
-void invoke_rcu_callbacks(void)
-{
-        if (rcu_scheduler_fully_active)
-                raise_softirq(RCU_SOFTIRQ);
-}
-
-#ifdef CONFIG_RCU_TRACE
-
-/*
- * There is no callback kthread, so this thread is never it.
- */
-static bool rcu_is_callbacks_kthread(void)
-{
-        return false;
-}
-
-#endif /* #ifdef CONFIG_RCU_TRACE */
-
-static int __init rcu_scheduler_really_started(void)
-{
-        rcu_scheduler_fully_active = 1;
-        open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
-        raise_softirq(RCU_SOFTIRQ);  /* Invoke any callbacks from early boot. */
-        return 0;
-}
-early_initcall(rcu_scheduler_really_started);
-
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 #include <linux/kernel_stat.h>