5 files changed, 70 insertions, 26 deletions

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 03cda7bed985..7142ee3304ab 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -118,7 +118,6 @@ static inline int rcu_preempt_depth(void)
 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
 
 /* Internal to kernel */
-extern void rcu_init(void);
 extern void rcu_sched_qs(int cpu);
 extern void rcu_bh_qs(int cpu);
 extern void rcu_check_callbacks(int cpu, int user);
diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 13877cb93a60..ea025a611fcc 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -27,7 +27,9 @@
 
 #include <linux/cache.h>
 
-#define rcu_init_sched()        do { } while (0)
+static inline void rcu_init(void)
+{
+}
 
 #ifdef CONFIG_TINY_RCU
 
@@ -125,16 +127,12 @@ static inline void rcu_cpu_stall_reset(void)
 }
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
-
 extern int rcu_scheduler_active __read_mostly;
 extern void rcu_scheduler_starting(void);
-
 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
-
 static inline void rcu_scheduler_starting(void)
 {
 }
-
 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 
 #endif /* __LINUX_RCUTINY_H */
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 95518e628794..c0e96833aa73 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -30,6 +30,7 @@
 #ifndef __LINUX_RCUTREE_H
 #define __LINUX_RCUTREE_H
 
+extern void rcu_init(void);
 extern void rcu_note_context_switch(int cpu);
 extern int rcu_needs_cpu(int cpu);
 extern void rcu_cpu_stall_reset(void);
diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c
index d806735342ac..86eef29cdfb2 100644
--- a/kernel/rcutiny.c
+++ b/kernel/rcutiny.c
@@ -59,8 +59,15 @@ int rcu_scheduler_active __read_mostly;
 EXPORT_SYMBOL_GPL(rcu_scheduler_active);
 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 
+/* Controls for rcu_cbs() kthread, replacing RCU_SOFTIRQ used previously. */
+static struct task_struct *rcu_cbs_task;
+static DECLARE_WAIT_QUEUE_HEAD(rcu_cbs_wq);
+static unsigned long have_rcu_cbs;
+static void invoke_rcu_cbs(void);
+
 /* Forward declarations for rcutiny_plugin.h. */
-static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp);
+static void rcu_process_callbacks(struct rcu_ctrlblk *rcp);
+static int rcu_cbs(void *arg);
 static void __call_rcu(struct rcu_head *head,
                        void (*func)(struct rcu_head *rcu),
                        struct rcu_ctrlblk *rcp);
@@ -123,7 +130,7 @@ void rcu_sched_qs(int cpu)
 {
         if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
             rcu_qsctr_help(&rcu_bh_ctrlblk))
-                raise_softirq(RCU_SOFTIRQ);
+                invoke_rcu_cbs();
 }
 
 /*
@@ -132,7 +139,7 @@ void rcu_sched_qs(int cpu)
 void rcu_bh_qs(int cpu)
 {
         if (rcu_qsctr_help(&rcu_bh_ctrlblk))
-                raise_softirq(RCU_SOFTIRQ);
+                invoke_rcu_cbs();
 }
 
 /*
@@ -152,10 +159,10 @@ void rcu_check_callbacks(int cpu, int user)
 }
 
 /*
- * Helper function for rcu_process_callbacks() that operates on the
- * specified rcu_ctrlkblk structure.
+ * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure
+ * whose grace period has elapsed.
  */
-static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
+static void rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 {
         struct rcu_head *next, *list;
         unsigned long flags;
@@ -180,19 +187,52 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
                 next = list->next;
                 prefetch(next);
                 debug_rcu_head_unqueue(list);
+                local_bh_disable();
                 list->func(list);
+                local_bh_enable();
                 list = next;
         }
 }
 
 /*
- * Invoke any callbacks whose grace period has completed.
+ * This kthread invokes RCU callbacks whose grace periods have
+ * elapsed.  It is awakened as needed, and takes the place of the
+ * RCU_SOFTIRQ that was used previously for this purpose.
+ * This is a kthread, but it is never stopped, at least not until
+ * the system goes down.
+ */
+static int rcu_cbs(void *arg)
+{
+        unsigned long work;
+        unsigned long flags;
+
+        for (;;) {
+                wait_event(rcu_cbs_wq, have_rcu_cbs != 0);
+                local_irq_save(flags);
+                work = have_rcu_cbs;
+                have_rcu_cbs = 0;
+                local_irq_restore(flags);
+                if (work) {
+                        rcu_process_callbacks(&rcu_sched_ctrlblk);
+                        rcu_process_callbacks(&rcu_bh_ctrlblk);
+                        rcu_preempt_process_callbacks();
+                }
+        }
+
+        return 0;  /* Not reached, but needed to shut gcc up. */
+}
+
+/*
+ * Wake up rcu_cbs() to process callbacks now eligible for invocation.
  */
-static void rcu_process_callbacks(struct softirq_action *unused)
+static void invoke_rcu_cbs(void)
 {
-        __rcu_process_callbacks(&rcu_sched_ctrlblk);
-        __rcu_process_callbacks(&rcu_bh_ctrlblk);
-        rcu_preempt_process_callbacks();
+        unsigned long flags;
+
+        local_irq_save(flags);
+        have_rcu_cbs = 1;
+        wake_up(&rcu_cbs_wq);
+        local_irq_restore(flags);
 }
 
 /*
@@ -282,7 +322,12 @@ void rcu_barrier_sched(void)
 }
 EXPORT_SYMBOL_GPL(rcu_barrier_sched);
 
-void __init rcu_init(void)
+/*
+ * Spawn the kthread that invokes RCU callbacks.
+ */
+static int __init rcu_spawn_kthreads(void)
 {
-        open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
+        rcu_cbs_task = kthread_run(rcu_cbs, NULL, "rcu_cbs");
+        return 0;
 }
+early_initcall(rcu_spawn_kthreads);
diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h
index 6ceca4f745ff..95f9239df512 100644
--- a/kernel/rcutiny_plugin.h
+++ b/kernel/rcutiny_plugin.h
@@ -22,6 +22,8 @@
  * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
  */
 
+#include <linux/kthread.h>
+
 #ifdef CONFIG_TINY_PREEMPT_RCU
 
 #include <linux/delay.h>
@@ -164,9 +166,9 @@ static void rcu_preempt_cpu_qs(void)
         if (!rcu_preempt_blocked_readers_any())
                 rcu_preempt_ctrlblk.rcb.donetail = rcu_preempt_ctrlblk.nexttail;
 
-        /* If there are done callbacks, make RCU_SOFTIRQ process them. */
+        /* If there are done callbacks, cause them to be invoked. */
         if (*rcu_preempt_ctrlblk.rcb.donetail != NULL)
-                raise_softirq(RCU_SOFTIRQ);
+                invoke_rcu_cbs();
 }
 
 /*
@@ -374,7 +376,7 @@ static void rcu_preempt_check_callbacks(void)
                 rcu_preempt_cpu_qs();
         if (&rcu_preempt_ctrlblk.rcb.rcucblist !=
             rcu_preempt_ctrlblk.rcb.donetail)
-                raise_softirq(RCU_SOFTIRQ);
+                invoke_rcu_cbs();
         if (rcu_preempt_gp_in_progress() &&
             rcu_cpu_blocking_cur_gp() &&
             rcu_preempt_running_reader())
@@ -383,7 +385,7 @@ static void rcu_preempt_check_callbacks(void)
 
 /*
  * TINY_PREEMPT_RCU has an extra callback-list tail pointer to
- * update, so this is invoked from __rcu_process_callbacks() to
+ * update, so this is invoked from rcu_process_callbacks() to
  * handle that case.  Of course, it is invoked for all flavors of
  * RCU, but RCU callbacks can appear only on one of the lists, and
  * neither ->nexttail nor ->donetail can possibly be NULL, so there
@@ -400,7 +402,7 @@ static void rcu_preempt_remove_callbacks(struct rcu_ctrlblk *rcp)
  */
 static void rcu_preempt_process_callbacks(void)
 {
-        __rcu_process_callbacks(&rcu_preempt_ctrlblk.rcb);
+        rcu_process_callbacks(&rcu_preempt_ctrlblk.rcb);
 }
 
 /*
@@ -599,14 +601,13 @@ static void rcu_preempt_process_callbacks(void)
 #endif /* #else #ifdef CONFIG_TINY_PREEMPT_RCU */
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
-
 #include <linux/kernel_stat.h>
 
 /*
  * During boot, we forgive RCU lockdep issues.  After this function is
  * invoked, we start taking RCU lockdep issues seriously.
  */
-void rcu_scheduler_starting(void)
+void __init rcu_scheduler_starting(void)
 {
         WARN_ON(nr_context_switches() > 0);
         rcu_scheduler_active = 1;