1 files changed, 91 insertions, 60 deletions

diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c
index 196ec02f8be0..7bbac7d0f5ab 100644
--- a/kernel/rcutiny.c
+++ b/kernel/rcutiny.c
@@ -35,29 +35,23 @@
 #include <linux/init.h>
 #include <linux/time.h>
 #include <linux/cpu.h>
+#include <linux/prefetch.h>
+
+/* Controls for rcu_kthread() kthread, replacing RCU_SOFTIRQ used previously. */
+static struct task_struct *rcu_kthread_task;
+static DECLARE_WAIT_QUEUE_HEAD(rcu_kthread_wq);
+static unsigned long have_rcu_kthread_work;
+
+/* Forward declarations for rcutiny_plugin.h. */
+struct rcu_ctrlblk;
+static void invoke_rcu_kthread(void);
+static void rcu_process_callbacks(struct rcu_ctrlblk *rcp);
+static int rcu_kthread(void *arg);
+static void __call_rcu(struct rcu_head *head,
+                       void (*func)(struct rcu_head *rcu),
+                       struct rcu_ctrlblk *rcp);
 
-/* Global control variables for rcupdate callback mechanism. */
-struct rcu_ctrlblk {
-        struct rcu_head *rcucblist;     /* List of pending callbacks (CBs). */
-        struct rcu_head **donetail;     /* ->next pointer of last "done" CB. */
-        struct rcu_head **curtail;      /* ->next pointer of last CB. */
-};
-
-/* Definition for rcupdate control block. */
-static struct rcu_ctrlblk rcu_sched_ctrlblk = {
-        .donetail       = &rcu_sched_ctrlblk.rcucblist,
-        .curtail        = &rcu_sched_ctrlblk.rcucblist,
-};
-
-static struct rcu_ctrlblk rcu_bh_ctrlblk = {
-        .donetail       = &rcu_bh_ctrlblk.rcucblist,
-        .curtail        = &rcu_bh_ctrlblk.rcucblist,
-};
-
-#ifdef CONFIG_DEBUG_LOCK_ALLOC
-int rcu_scheduler_active __read_mostly;
-EXPORT_SYMBOL_GPL(rcu_scheduler_active);
-#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+#include "rcutiny_plugin.h"
 
 #ifdef CONFIG_NO_HZ
 
@@ -86,36 +80,45 @@ void rcu_exit_nohz(void)
 #endif /* #ifdef CONFIG_NO_HZ */
 
 /*
- * Helper function for rcu_qsctr_inc() and rcu_bh_qsctr_inc().
- * Also disable irqs to avoid confusion due to interrupt handlers
+ * Helper function for rcu_sched_qs() and rcu_bh_qs().
+ * Also irqs are disabled to avoid confusion due to interrupt handlers
  * invoking call_rcu().
  */
 static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
 {
-        unsigned long flags;
-
-        local_irq_save(flags);
         if (rcp->rcucblist != NULL &&
             rcp->donetail != rcp->curtail) {
                 rcp->donetail = rcp->curtail;
-                local_irq_restore(flags);
                 return 1;
         }
-        local_irq_restore(flags);
 
         return 0;
 }
 
 /*
+ * Wake up rcu_kthread() to process callbacks now eligible for invocation
+ * or to boost readers.
+ */
+static void invoke_rcu_kthread(void)
+{
+        have_rcu_kthread_work = 1;
+        wake_up(&rcu_kthread_wq);
+}
+
+/*
  * Record an rcu quiescent state.  And an rcu_bh quiescent state while we
  * are at it, given that any rcu quiescent state is also an rcu_bh
  * quiescent state.  Use "+" instead of "||" to defeat short circuiting.
  */
 void rcu_sched_qs(int cpu)
 {
+        unsigned long flags;
+
+        local_irq_save(flags);
         if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
             rcu_qsctr_help(&rcu_bh_ctrlblk))
-                raise_softirq(RCU_SOFTIRQ);
+                invoke_rcu_kthread();
+        local_irq_restore(flags);
 }
 
 /*
@@ -123,8 +126,12 @@ void rcu_sched_qs(int cpu)
  */
 void rcu_bh_qs(int cpu)
 {
+        unsigned long flags;
+
+        local_irq_save(flags);
         if (rcu_qsctr_help(&rcu_bh_ctrlblk))
-                raise_softirq(RCU_SOFTIRQ);
+                invoke_rcu_kthread();
+        local_irq_restore(flags);
 }
 
 /*
@@ -140,16 +147,18 @@ void rcu_check_callbacks(int cpu, int user)
                 rcu_sched_qs(cpu);
         else if (!in_softirq())
                 rcu_bh_qs(cpu);
+        rcu_preempt_check_callbacks();
 }
 
 /*
- * 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;
+        RCU_TRACE(int cb_count = 0);
 
         /* If no RCU callbacks ready to invoke, just return. */
         if (&rcp->rcucblist == rcp->donetail)
@@ -162,6 +171,7 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
         *rcp->donetail = NULL;
         if (rcp->curtail == rcp->donetail)
                 rcp->curtail = &rcp->rcucblist;
+        rcu_preempt_remove_callbacks(rcp);
         rcp->donetail = &rcp->rcucblist;
         local_irq_restore(flags);
 
@@ -170,18 +180,45 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
                 next = list->next;
                 prefetch(next);
                 debug_rcu_head_unqueue(list);
-                list->func(list);
+                local_bh_disable();
+                __rcu_reclaim(list);
+                local_bh_enable();
                 list = next;
+                RCU_TRACE(cb_count++);
         }
+        RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));
 }
 
 /*
- * 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 void rcu_process_callbacks(struct softirq_action *unused)
+static int rcu_kthread(void *arg)
 {
-        __rcu_process_callbacks(&rcu_sched_ctrlblk);
-        __rcu_process_callbacks(&rcu_bh_ctrlblk);
+        unsigned long work;
+        unsigned long morework;
+        unsigned long flags;
+
+        for (;;) {
+                wait_event_interruptible(rcu_kthread_wq,
+                                         have_rcu_kthread_work != 0);
+                morework = rcu_boost();
+                local_irq_save(flags);
+                work = have_rcu_kthread_work;
+                have_rcu_kthread_work = morework;
+                local_irq_restore(flags);
+                if (work) {
+                        rcu_process_callbacks(&rcu_sched_ctrlblk);
+                        rcu_process_callbacks(&rcu_bh_ctrlblk);
+                        rcu_preempt_process_callbacks();
+                }
+                schedule_timeout_interruptible(1); /* Leave CPU for others. */
+        }
+
+        return 0;  /* Not reached, but needed to shut gcc up. */
 }
 
 /*
@@ -219,19 +256,20 @@ static void __call_rcu(struct rcu_head *head,
         local_irq_save(flags);
         *rcp->curtail = head;
         rcp->curtail = &head->next;
+        RCU_TRACE(rcp->qlen++);
         local_irq_restore(flags);
 }
 
 /*
- * Post an RCU callback to be invoked after the end of an RCU grace
+ * Post an RCU callback to be invoked after the end of an RCU-sched grace
  * period.  But since we have but one CPU, that would be after any
  * quiescent state.
  */
-void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
+void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
 {
         __call_rcu(head, func, &rcu_sched_ctrlblk);
 }
-EXPORT_SYMBOL_GPL(call_rcu);
+EXPORT_SYMBOL_GPL(call_rcu_sched);
 
 /*
  * Post an RCU bottom-half callback to be invoked after any subsequent
@@ -243,20 +281,6 @@ void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
 }
 EXPORT_SYMBOL_GPL(call_rcu_bh);
 
-void rcu_barrier(void)
-{
-        struct rcu_synchronize rcu;
-
-        init_rcu_head_on_stack(&rcu.head);
-        init_completion(&rcu.completion);
-        /* Will wake me after RCU finished. */
-        call_rcu(&rcu.head, wakeme_after_rcu);
-        /* Wait for it. */
-        wait_for_completion(&rcu.completion);
-        destroy_rcu_head_on_stack(&rcu.head);
-}
-EXPORT_SYMBOL_GPL(rcu_barrier);
-
 void rcu_barrier_bh(void)
 {
         struct rcu_synchronize rcu;
@@ -285,9 +309,16 @@ 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);
-}
+        struct sched_param sp;
 
-#include "rcutiny_plugin.h"
+        rcu_kthread_task = kthread_run(rcu_kthread, NULL, "rcu_kthread");
+        sp.sched_priority = RCU_BOOST_PRIO;
+        sched_setscheduler_nocheck(rcu_kthread_task, SCHED_FIFO, &sp);
+        return 0;
+}
+early_initcall(rcu_spawn_kthreads);