Merge branch 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

* 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  rcu: Move RCU_BOOST #ifdefs to header file
  rcu: use softirq instead of kthreads except when RCU_BOOST=y
  rcu: Use softirq to address performance regression
  rcu: Simplify curing of load woes

5 files changed, 461 insertions, 402 deletions

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 89419ff92e99..7e59ffb3d0ba 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -87,6 +87,8 @@ static struct rcu_state *rcu_state;
 int rcu_scheduler_active __read_mostly;
 EXPORT_SYMBOL_GPL(rcu_scheduler_active);
 
+#ifdef CONFIG_RCU_BOOST
+
 /*
  * Control variables for per-CPU and per-rcu_node kthreads.  These
  * handle all flavors of RCU.
@@ -98,8 +100,11 @@ DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
 DEFINE_PER_CPU(char, rcu_cpu_has_work);
 static char rcu_kthreads_spawnable;
 
+#endif /* #ifdef CONFIG_RCU_BOOST */
+
 static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu);
-static void invoke_rcu_cpu_kthread(void);
+static void invoke_rcu_core(void);
+static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp);
 
 #define RCU_KTHREAD_PRIO 1      /* RT priority for per-CPU kthreads. */
 
@@ -1088,14 +1093,8 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
         int need_report = 0;
         struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
         struct rcu_node *rnp;
-        struct task_struct *t;
 
-        /* Stop the CPU's kthread. */
-        t = per_cpu(rcu_cpu_kthread_task, cpu);
-        if (t != NULL) {
-                per_cpu(rcu_cpu_kthread_task, cpu) = NULL;
-                kthread_stop(t);
-        }
+        rcu_stop_cpu_kthread(cpu);
 
         /* Exclude any attempts to start a new grace period. */
         raw_spin_lock_irqsave(&rsp->onofflock, flags);
@@ -1231,7 +1230,7 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
 
         /* Re-raise the RCU softirq if there are callbacks remaining. */
         if (cpu_has_callbacks_ready_to_invoke(rdp))
-                invoke_rcu_cpu_kthread();
+                invoke_rcu_core();
 }
 
 /*
@@ -1277,7 +1276,7 @@ void rcu_check_callbacks(int cpu, int user)
         }
         rcu_preempt_check_callbacks(cpu);
         if (rcu_pending(cpu))
-                invoke_rcu_cpu_kthread();
+                invoke_rcu_core();
 }
 
 #ifdef CONFIG_SMP
@@ -1442,13 +1441,14 @@ __rcu_process_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
         }
 
         /* If there are callbacks ready, invoke them. */
-        rcu_do_batch(rsp, rdp);
+        if (cpu_has_callbacks_ready_to_invoke(rdp))
+                invoke_rcu_callbacks(rsp, rdp);
 }
 
 /*
  * Do softirq processing for the current CPU.
  */
-static void rcu_process_callbacks(void)
+static void rcu_process_callbacks(struct softirq_action *unused)
 {
         __rcu_process_callbacks(&rcu_sched_state,
                                 &__get_cpu_var(rcu_sched_data));
@@ -1465,342 +1465,20 @@ static void rcu_process_callbacks(void)
  * the current CPU with interrupts disabled, the rcu_cpu_kthread_task
  * cannot disappear out from under us.
  */
-static void invoke_rcu_cpu_kthread(void)
-{
-        unsigned long flags;
-
-        local_irq_save(flags);
-        __this_cpu_write(rcu_cpu_has_work, 1);
-        if (__this_cpu_read(rcu_cpu_kthread_task) == NULL) {
-                local_irq_restore(flags);
-                return;
-        }
-        wake_up_process(__this_cpu_read(rcu_cpu_kthread_task));
-        local_irq_restore(flags);
-}
-
-/*
- * Wake up the specified per-rcu_node-structure kthread.
- * Because the per-rcu_node kthreads are immortal, we don't need
- * to do anything to keep them alive.
- */
-static void invoke_rcu_node_kthread(struct rcu_node *rnp)
-{
-        struct task_struct *t;
-
-        t = rnp->node_kthread_task;
-        if (t != NULL)
-                wake_up_process(t);
-}
-
-/*
- * Set the specified CPU's kthread to run RT or not, as specified by
- * the to_rt argument.  The CPU-hotplug locks are held, so the task
- * is not going away.
- */
-static void rcu_cpu_kthread_setrt(int cpu, int to_rt)
-{
-        int policy;
-        struct sched_param sp;
-        struct task_struct *t;
-
-        t = per_cpu(rcu_cpu_kthread_task, cpu);
-        if (t == NULL)
-                return;
-        if (to_rt) {
-                policy = SCHED_FIFO;
-                sp.sched_priority = RCU_KTHREAD_PRIO;
-        } else {
-                policy = SCHED_NORMAL;
-                sp.sched_priority = 0;
-        }
-        sched_setscheduler_nocheck(t, policy, &sp);
-}
-
-/*
- * Timer handler to initiate the waking up of per-CPU kthreads that
- * have yielded the CPU due to excess numbers of RCU callbacks.
- * We wake up the per-rcu_node kthread, which in turn will wake up
- * the booster kthread.
- */
-static void rcu_cpu_kthread_timer(unsigned long arg)
-{
-        struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, arg);
-        struct rcu_node *rnp = rdp->mynode;
-
-        atomic_or(rdp->grpmask, &rnp->wakemask);
-        invoke_rcu_node_kthread(rnp);
-}
-
-/*
- * Drop to non-real-time priority and yield, but only after posting a
- * timer that will cause us to regain our real-time priority if we
- * remain preempted.  Either way, we restore our real-time priority
- * before returning.
- */
-static void rcu_yield(void (*f)(unsigned long), unsigned long arg)
-{
-        struct sched_param sp;
-        struct timer_list yield_timer;
-
-        setup_timer_on_stack(&yield_timer, f, arg);
-        mod_timer(&yield_timer, jiffies + 2);
-        sp.sched_priority = 0;
-        sched_setscheduler_nocheck(current, SCHED_NORMAL, &sp);
-        set_user_nice(current, 19);
-        schedule();
-        sp.sched_priority = RCU_KTHREAD_PRIO;
-        sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
-        del_timer(&yield_timer);
-}
-
-/*
- * Handle cases where the rcu_cpu_kthread() ends up on the wrong CPU.
- * This can happen while the corresponding CPU is either coming online
- * or going offline.  We cannot wait until the CPU is fully online
- * before starting the kthread, because the various notifier functions
- * can wait for RCU grace periods.  So we park rcu_cpu_kthread() until
- * the corresponding CPU is online.
- *
- * Return 1 if the kthread needs to stop, 0 otherwise.
- *
- * Caller must disable bh.  This function can momentarily enable it.
- */
-static int rcu_cpu_kthread_should_stop(int cpu)
-{
-        while (cpu_is_offline(cpu) ||
-               !cpumask_equal(&current->cpus_allowed, cpumask_of(cpu)) ||
-               smp_processor_id() != cpu) {
-                if (kthread_should_stop())
-                        return 1;
-                per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
-                per_cpu(rcu_cpu_kthread_cpu, cpu) = raw_smp_processor_id();
-                local_bh_enable();
-                schedule_timeout_uninterruptible(1);
-                if (!cpumask_equal(&current->cpus_allowed, cpumask_of(cpu)))
-                        set_cpus_allowed_ptr(current, cpumask_of(cpu));
-                local_bh_disable();
-        }
-        per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu;
-        return 0;
-}
-
-/*
- * Per-CPU kernel thread that invokes RCU callbacks.  This replaces the
- * earlier RCU softirq.
- */
-static int rcu_cpu_kthread(void *arg)
-{
-        int cpu = (int)(long)arg;
-        unsigned long flags;
-        int spincnt = 0;
-        unsigned int *statusp = &per_cpu(rcu_cpu_kthread_status, cpu);
-        char work;
-        char *workp = &per_cpu(rcu_cpu_has_work, cpu);
-
-        for (;;) {
-                *statusp = RCU_KTHREAD_WAITING;
-                rcu_wait(*workp != 0 || kthread_should_stop());
-                local_bh_disable();
-                if (rcu_cpu_kthread_should_stop(cpu)) {
-                        local_bh_enable();
-                        break;
-                }
-                *statusp = RCU_KTHREAD_RUNNING;
-                per_cpu(rcu_cpu_kthread_loops, cpu)++;
-                local_irq_save(flags);
-                work = *workp;
-                *workp = 0;
-                local_irq_restore(flags);
-                if (work)
-                        rcu_process_callbacks();
-                local_bh_enable();
-                if (*workp != 0)
-                        spincnt++;
-                else
-                        spincnt = 0;
-                if (spincnt > 10) {
-                        *statusp = RCU_KTHREAD_YIELDING;
-                        rcu_yield(rcu_cpu_kthread_timer, (unsigned long)cpu);
-                        spincnt = 0;
-                }
-        }
-        *statusp = RCU_KTHREAD_STOPPED;
-        return 0;
-}
-
-/*
- * Spawn a per-CPU kthread, setting up affinity and priority.
- * Because the CPU hotplug lock is held, no other CPU will be attempting
- * to manipulate rcu_cpu_kthread_task.  There might be another CPU
- * attempting to access it during boot, but the locking in kthread_bind()
- * will enforce sufficient ordering.
- */
-static int __cpuinit rcu_spawn_one_cpu_kthread(int cpu)
+static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
 {
-        struct sched_param sp;
-        struct task_struct *t;
-
-        if (!rcu_kthreads_spawnable ||
-            per_cpu(rcu_cpu_kthread_task, cpu) != NULL)
-                return 0;
-        t = kthread_create(rcu_cpu_kthread, (void *)(long)cpu, "rcuc%d", cpu);
-        if (IS_ERR(t))
-                return PTR_ERR(t);
-        kthread_bind(t, cpu);
-        per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu;
-        WARN_ON_ONCE(per_cpu(rcu_cpu_kthread_task, cpu) != NULL);
-        per_cpu(rcu_cpu_kthread_task, cpu) = t;
-        sp.sched_priority = RCU_KTHREAD_PRIO;
-        sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
-        return 0;
-}
-
-/*
- * Per-rcu_node kthread, which is in charge of waking up the per-CPU
- * kthreads when needed.  We ignore requests to wake up kthreads
- * for offline CPUs, which is OK because force_quiescent_state()
- * takes care of this case.
- */
-static int rcu_node_kthread(void *arg)
-{
-        int cpu;
-        unsigned long flags;
-        unsigned long mask;
-        struct rcu_node *rnp = (struct rcu_node *)arg;
-        struct sched_param sp;
-        struct task_struct *t;
-
-        for (;;) {
-                rnp->node_kthread_status = RCU_KTHREAD_WAITING;
-                rcu_wait(atomic_read(&rnp->wakemask) != 0);
-                rnp->node_kthread_status = RCU_KTHREAD_RUNNING;
-                raw_spin_lock_irqsave(&rnp->lock, flags);
-                mask = atomic_xchg(&rnp->wakemask, 0);
-                rcu_initiate_boost(rnp, flags); /* releases rnp->lock. */
-                for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1) {
-                        if ((mask & 0x1) == 0)
-                                continue;
-                        preempt_disable();
-                        t = per_cpu(rcu_cpu_kthread_task, cpu);
-                        if (!cpu_online(cpu) || t == NULL) {
-                                preempt_enable();
-                                continue;
-                        }
-                        per_cpu(rcu_cpu_has_work, cpu) = 1;
-                        sp.sched_priority = RCU_KTHREAD_PRIO;
-                        sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
-                        preempt_enable();
-                }
-        }
-        /* NOTREACHED */
-        rnp->node_kthread_status = RCU_KTHREAD_STOPPED;
-        return 0;
-}
-
-/*
- * Set the per-rcu_node kthread's affinity to cover all CPUs that are
- * served by the rcu_node in question.  The CPU hotplug lock is still
- * held, so the value of rnp->qsmaskinit will be stable.
- *
- * We don't include outgoingcpu in the affinity set, use -1 if there is
- * no outgoing CPU.  If there are no CPUs left in the affinity set,
- * this function allows the kthread to execute on any CPU.
- */
-static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
-{
-        cpumask_var_t cm;
-        int cpu;
-        unsigned long mask = rnp->qsmaskinit;
-
-        if (rnp->node_kthread_task == NULL)
-                return;
-        if (!alloc_cpumask_var(&cm, GFP_KERNEL))
+        if (likely(!rsp->boost)) {
+                rcu_do_batch(rsp, rdp);
                 return;
-        cpumask_clear(cm);
-        for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1)
-                if ((mask & 0x1) && cpu != outgoingcpu)
-                        cpumask_set_cpu(cpu, cm);
-        if (cpumask_weight(cm) == 0) {
-                cpumask_setall(cm);
-                for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++)
-                        cpumask_clear_cpu(cpu, cm);
-                WARN_ON_ONCE(cpumask_weight(cm) == 0);
         }
-        set_cpus_allowed_ptr(rnp->node_kthread_task, cm);
-        rcu_boost_kthread_setaffinity(rnp, cm);
-        free_cpumask_var(cm);
+        invoke_rcu_callbacks_kthread();
 }
 
-/*
- * Spawn a per-rcu_node kthread, setting priority and affinity.
- * Called during boot before online/offline can happen, or, if
- * during runtime, with the main CPU-hotplug locks held.  So only
- * one of these can be executing at a time.
- */
-static int __cpuinit rcu_spawn_one_node_kthread(struct rcu_state *rsp,
-                                                struct rcu_node *rnp)
+static void invoke_rcu_core(void)
 {
-        unsigned long flags;
-        int rnp_index = rnp - &rsp->node[0];
-        struct sched_param sp;
-        struct task_struct *t;
-
-        if (!rcu_kthreads_spawnable ||
-            rnp->qsmaskinit == 0)
-                return 0;
-        if (rnp->node_kthread_task == NULL) {
-                t = kthread_create(rcu_node_kthread, (void *)rnp,
-                                   "rcun%d", rnp_index);
-                if (IS_ERR(t))
-                        return PTR_ERR(t);
-                raw_spin_lock_irqsave(&rnp->lock, flags);
-                rnp->node_kthread_task = t;
-                raw_spin_unlock_irqrestore(&rnp->lock, flags);
-                sp.sched_priority = 99;
-                sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
-        }
-        return rcu_spawn_one_boost_kthread(rsp, rnp, rnp_index);
+        raise_softirq(RCU_SOFTIRQ);
 }
 
-static void rcu_wake_one_boost_kthread(struct rcu_node *rnp);
-
-/*
- * Spawn all kthreads -- called as soon as the scheduler is running.
- */
-static int __init rcu_spawn_kthreads(void)
-{
-        int cpu;
-        struct rcu_node *rnp;
-        struct task_struct *t;
-
-        rcu_kthreads_spawnable = 1;
-        for_each_possible_cpu(cpu) {
-                per_cpu(rcu_cpu_has_work, cpu) = 0;
-                if (cpu_online(cpu)) {
-                        (void)rcu_spawn_one_cpu_kthread(cpu);
-                        t = per_cpu(rcu_cpu_kthread_task, cpu);
-                        if (t)
-                                wake_up_process(t);
-                }
-        }
-        rnp = rcu_get_root(rcu_state);
-        (void)rcu_spawn_one_node_kthread(rcu_state, rnp);
-        if (rnp->node_kthread_task)
-                wake_up_process(rnp->node_kthread_task);
-        if (NUM_RCU_NODES > 1) {
-                rcu_for_each_leaf_node(rcu_state, rnp) {
-                        (void)rcu_spawn_one_node_kthread(rcu_state, rnp);
-                        t = rnp->node_kthread_task;
-                        if (t)
-                                wake_up_process(t);
-                        rcu_wake_one_boost_kthread(rnp);
-                }
-        }
-        return 0;
-}
-early_initcall(rcu_spawn_kthreads);
-
 static void
 __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
            struct rcu_state *rsp)
@@ -2207,44 +1885,6 @@ static void __cpuinit rcu_prepare_cpu(int cpu)
         rcu_preempt_init_percpu_data(cpu);
 }
 
-static void __cpuinit rcu_prepare_kthreads(int cpu)
-{
-        struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
-        struct rcu_node *rnp = rdp->mynode;
-
-        /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
-        if (rcu_kthreads_spawnable) {
-                (void)rcu_spawn_one_cpu_kthread(cpu);
-                if (rnp->node_kthread_task == NULL)
-                        (void)rcu_spawn_one_node_kthread(rcu_state, rnp);
-        }
-}
-
-/*
- * kthread_create() creates threads in TASK_UNINTERRUPTIBLE state,
- * but the RCU threads are woken on demand, and if demand is low this
- * could be a while triggering the hung task watchdog.
- *
- * In order to avoid this, poke all tasks once the CPU is fully
- * up and running.
- */
-static void __cpuinit rcu_online_kthreads(int cpu)
-{
-        struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
-        struct rcu_node *rnp = rdp->mynode;
-        struct task_struct *t;
-
-        t = per_cpu(rcu_cpu_kthread_task, cpu);
-        if (t)
-                wake_up_process(t);
-
-        t = rnp->node_kthread_task;
-        if (t)
-                wake_up_process(t);
-
-        rcu_wake_one_boost_kthread(rnp);
-}
-
 /*
  * Handle CPU online/offline notification events.
  */
@@ -2262,7 +1902,6 @@ static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
                 rcu_prepare_kthreads(cpu);
                 break;
         case CPU_ONLINE:
-                rcu_online_kthreads(cpu);
         case CPU_DOWN_FAILED:
                 rcu_node_kthread_setaffinity(rnp, -1);
                 rcu_cpu_kthread_setrt(cpu, 1);
@@ -2410,6 +2049,7 @@ void __init rcu_init(void)
         rcu_init_one(&rcu_sched_state, &rcu_sched_data);
         rcu_init_one(&rcu_bh_state, &rcu_bh_data);
         __rcu_init_preempt();
+         open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
 
         /*
          * We don't need protection against CPU-hotplug here because
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index 7b9a08b4aaea..01b2ccda26fb 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -369,6 +369,7 @@ struct rcu_state {
                                                 /*  period because */
                                                 /*  force_quiescent_state() */
                                                 /*  was running. */
+        u8      boost;                          /* Subject to priority boost. */
         unsigned long gpnum;                    /* Current gp number. */
         unsigned long completed;                /* # of last completed gp. */
 
@@ -426,6 +427,7 @@ static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp);
 #ifdef CONFIG_HOTPLUG_CPU
 static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp,
                                       unsigned long flags);
+static void rcu_stop_cpu_kthread(int cpu);
 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
 static void rcu_print_detail_task_stall(struct rcu_state *rsp);
 static void rcu_print_task_stall(struct rcu_node *rnp);
@@ -450,11 +452,19 @@ static void rcu_preempt_send_cbs_to_online(void);
 static void __init __rcu_init_preempt(void);
 static void rcu_needs_cpu_flush(void);
 static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags);
+static void rcu_preempt_boost_start_gp(struct rcu_node *rnp);
+static void invoke_rcu_callbacks_kthread(void);
+#ifdef CONFIG_RCU_BOOST
+static void rcu_preempt_do_callbacks(void);
 static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp,
                                           cpumask_var_t cm);
-static void rcu_preempt_boost_start_gp(struct rcu_node *rnp);
 static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
                                                  struct rcu_node *rnp,
                                                  int rnp_index);
+static void invoke_rcu_node_kthread(struct rcu_node *rnp);
+static void rcu_yield(void (*f)(unsigned long), unsigned long arg);
+#endif /* #ifdef CONFIG_RCU_BOOST */
+static void rcu_cpu_kthread_setrt(int cpu, int to_rt);
+static void __cpuinit rcu_prepare_kthreads(int cpu);
 
 #endif /* #ifndef RCU_TREE_NONCORE */
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index c8bff3099a89..14dc7dd00902 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -602,6 +602,15 @@ static void rcu_preempt_process_callbacks(void)
                                 &__get_cpu_var(rcu_preempt_data));
 }
 
+#ifdef CONFIG_RCU_BOOST
+
+static void rcu_preempt_do_callbacks(void)
+{
+        rcu_do_batch(&rcu_preempt_state, &__get_cpu_var(rcu_preempt_data));
+}
+
+#endif /* #ifdef CONFIG_RCU_BOOST */
+
 /*
  * Queue a preemptible-RCU callback for invocation after a grace period.
  */
@@ -1249,6 +1258,23 @@ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
 }
 
 /*
+ * Wake up the per-CPU kthread to invoke RCU callbacks.
+ */
+static void invoke_rcu_callbacks_kthread(void)
+{
+        unsigned long flags;
+
+        local_irq_save(flags);
+        __this_cpu_write(rcu_cpu_has_work, 1);
+        if (__this_cpu_read(rcu_cpu_kthread_task) == NULL) {
+                local_irq_restore(flags);
+                return;
+        }
+        wake_up_process(__this_cpu_read(rcu_cpu_kthread_task));
+        local_irq_restore(flags);
+}
+
+/*
  * Set the affinity of the boost kthread.  The CPU-hotplug locks are
  * held, so no one should be messing with the existence of the boost
  * kthread.
@@ -1288,6 +1314,7 @@ static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
 
         if (&rcu_preempt_state != rsp)
                 return 0;
+        rsp->boost = 1;
         if (rnp->boost_kthread_task != NULL)
                 return 0;
         t = kthread_create(rcu_boost_kthread, (void *)rnp,
@@ -1299,13 +1326,372 @@ static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
         raw_spin_unlock_irqrestore(&rnp->lock, flags);
         sp.sched_priority = RCU_KTHREAD_PRIO;
         sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
+        wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
         return 0;
 }
 
-static void __cpuinit rcu_wake_one_boost_kthread(struct rcu_node *rnp)
+#ifdef CONFIG_HOTPLUG_CPU
+
+/*
+ * Stop the RCU's per-CPU kthread when its CPU goes offline,.
+ */
+static void rcu_stop_cpu_kthread(int cpu)
 {
-        if (rnp->boost_kthread_task)
-                wake_up_process(rnp->boost_kthread_task);
+        struct task_struct *t;
+
+        /* Stop the CPU's kthread. */
+        t = per_cpu(rcu_cpu_kthread_task, cpu);
+        if (t != NULL) {
+                per_cpu(rcu_cpu_kthread_task, cpu) = NULL;
+                kthread_stop(t);
+        }
+}
+
+#endif /* #ifdef CONFIG_HOTPLUG_CPU */
+
+static void rcu_kthread_do_work(void)
+{
+        rcu_do_batch(&rcu_sched_state, &__get_cpu_var(rcu_sched_data));
+        rcu_do_batch(&rcu_bh_state, &__get_cpu_var(rcu_bh_data));
+        rcu_preempt_do_callbacks();
+}
+
+/*
+ * Wake up the specified per-rcu_node-structure kthread.
+ * Because the per-rcu_node kthreads are immortal, we don't need
+ * to do anything to keep them alive.
+ */
+static void invoke_rcu_node_kthread(struct rcu_node *rnp)
+{
+        struct task_struct *t;
+
+        t = rnp->node_kthread_task;
+        if (t != NULL)
+                wake_up_process(t);
+}
+
+/*
+ * Set the specified CPU's kthread to run RT or not, as specified by
+ * the to_rt argument.  The CPU-hotplug locks are held, so the task
+ * is not going away.
+ */
+static void rcu_cpu_kthread_setrt(int cpu, int to_rt)
+{
+        int policy;
+        struct sched_param sp;
+        struct task_struct *t;
+
+        t = per_cpu(rcu_cpu_kthread_task, cpu);
+        if (t == NULL)
+                return;
+        if (to_rt) {
+                policy = SCHED_FIFO;
+                sp.sched_priority = RCU_KTHREAD_PRIO;
+        } else {
+                policy = SCHED_NORMAL;
+                sp.sched_priority = 0;
+        }
+        sched_setscheduler_nocheck(t, policy, &sp);
+}
+
+/*
+ * Timer handler to initiate the waking up of per-CPU kthreads that
+ * have yielded the CPU due to excess numbers of RCU callbacks.
+ * We wake up the per-rcu_node kthread, which in turn will wake up
+ * the booster kthread.
+ */
+static void rcu_cpu_kthread_timer(unsigned long arg)
+{
+        struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, arg);
+        struct rcu_node *rnp = rdp->mynode;
+
+        atomic_or(rdp->grpmask, &rnp->wakemask);
+        invoke_rcu_node_kthread(rnp);
+}
+
+/*
+ * Drop to non-real-time priority and yield, but only after posting a
+ * timer that will cause us to regain our real-time priority if we
+ * remain preempted.  Either way, we restore our real-time priority
+ * before returning.
+ */
+static void rcu_yield(void (*f)(unsigned long), unsigned long arg)
+{
+        struct sched_param sp;
+        struct timer_list yield_timer;
+
+        setup_timer_on_stack(&yield_timer, f, arg);
+        mod_timer(&yield_timer, jiffies + 2);
+        sp.sched_priority = 0;
+        sched_setscheduler_nocheck(current, SCHED_NORMAL, &sp);
+        set_user_nice(current, 19);
+        schedule();
+        sp.sched_priority = RCU_KTHREAD_PRIO;
+        sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
+        del_timer(&yield_timer);
+}
+
+/*
+ * Handle cases where the rcu_cpu_kthread() ends up on the wrong CPU.
+ * This can happen while the corresponding CPU is either coming online
+ * or going offline.  We cannot wait until the CPU is fully online
+ * before starting the kthread, because the various notifier functions
+ * can wait for RCU grace periods.  So we park rcu_cpu_kthread() until
+ * the corresponding CPU is online.
+ *
+ * Return 1 if the kthread needs to stop, 0 otherwise.
+ *
+ * Caller must disable bh.  This function can momentarily enable it.
+ */
+static int rcu_cpu_kthread_should_stop(int cpu)
+{
+        while (cpu_is_offline(cpu) ||
+               !cpumask_equal(&current->cpus_allowed, cpumask_of(cpu)) ||
+               smp_processor_id() != cpu) {
+                if (kthread_should_stop())
+                        return 1;
+                per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
+                per_cpu(rcu_cpu_kthread_cpu, cpu) = raw_smp_processor_id();
+                local_bh_enable();
+                schedule_timeout_uninterruptible(1);
+                if (!cpumask_equal(&current->cpus_allowed, cpumask_of(cpu)))
+                        set_cpus_allowed_ptr(current, cpumask_of(cpu));
+                local_bh_disable();
+        }
+        per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu;
+        return 0;
+}
+
+/*
+ * Per-CPU kernel thread that invokes RCU callbacks.  This replaces the
+ * earlier RCU softirq.
+ */
+static int rcu_cpu_kthread(void *arg)
+{
+        int cpu = (int)(long)arg;
+        unsigned long flags;
+        int spincnt = 0;
+        unsigned int *statusp = &per_cpu(rcu_cpu_kthread_status, cpu);
+        char work;
+        char *workp = &per_cpu(rcu_cpu_has_work, cpu);
+
+        for (;;) {
+                *statusp = RCU_KTHREAD_WAITING;
+                rcu_wait(*workp != 0 || kthread_should_stop());
+                local_bh_disable();
+                if (rcu_cpu_kthread_should_stop(cpu)) {
+                        local_bh_enable();
+                        break;
+                }
+                *statusp = RCU_KTHREAD_RUNNING;
+                per_cpu(rcu_cpu_kthread_loops, cpu)++;
+                local_irq_save(flags);
+                work = *workp;
+                *workp = 0;
+                local_irq_restore(flags);
+                if (work)
+                        rcu_kthread_do_work();
+                local_bh_enable();
+                if (*workp != 0)
+                        spincnt++;
+                else
+                        spincnt = 0;
+                if (spincnt > 10) {
+                        *statusp = RCU_KTHREAD_YIELDING;
+                        rcu_yield(rcu_cpu_kthread_timer, (unsigned long)cpu);
+                        spincnt = 0;
+                }
+        }
+        *statusp = RCU_KTHREAD_STOPPED;
+        return 0;
+}
+
+/*
+ * Spawn a per-CPU kthread, setting up affinity and priority.
+ * Because the CPU hotplug lock is held, no other CPU will be attempting
+ * to manipulate rcu_cpu_kthread_task.  There might be another CPU
+ * attempting to access it during boot, but the locking in kthread_bind()
+ * will enforce sufficient ordering.
+ *
+ * Please note that we cannot simply refuse to wake up the per-CPU
+ * kthread because kthreads are created in TASK_UNINTERRUPTIBLE state,
+ * which can result in softlockup complaints if the task ends up being
+ * idle for more than a couple of minutes.
+ *
+ * However, please note also that we cannot bind the per-CPU kthread to its
+ * CPU until that CPU is fully online.  We also cannot wait until the
+ * CPU is fully online before we create its per-CPU kthread, as this would
+ * deadlock the system when CPU notifiers tried waiting for grace
+ * periods.  So we bind the per-CPU kthread to its CPU only if the CPU
+ * is online.  If its CPU is not yet fully online, then the code in
+ * rcu_cpu_kthread() will wait until it is fully online, and then do
+ * the binding.
+ */
+static int __cpuinit rcu_spawn_one_cpu_kthread(int cpu)
+{
+        struct sched_param sp;
+        struct task_struct *t;
+
+        if (!rcu_kthreads_spawnable ||
+            per_cpu(rcu_cpu_kthread_task, cpu) != NULL)
+                return 0;
+        t = kthread_create(rcu_cpu_kthread, (void *)(long)cpu, "rcuc%d", cpu);
+        if (IS_ERR(t))
+                return PTR_ERR(t);
+        if (cpu_online(cpu))
+                kthread_bind(t, cpu);
+        per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu;
+        WARN_ON_ONCE(per_cpu(rcu_cpu_kthread_task, cpu) != NULL);
+        sp.sched_priority = RCU_KTHREAD_PRIO;
+        sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
+        per_cpu(rcu_cpu_kthread_task, cpu) = t;
+        wake_up_process(t); /* Get to TASK_INTERRUPTIBLE quickly. */
+        return 0;
+}
+
+/*
+ * Per-rcu_node kthread, which is in charge of waking up the per-CPU
+ * kthreads when needed.  We ignore requests to wake up kthreads
+ * for offline CPUs, which is OK because force_quiescent_state()
+ * takes care of this case.
+ */
+static int rcu_node_kthread(void *arg)
+{
+        int cpu;
+        unsigned long flags;
+        unsigned long mask;
+        struct rcu_node *rnp = (struct rcu_node *)arg;
+        struct sched_param sp;
+        struct task_struct *t;
+
+        for (;;) {
+                rnp->node_kthread_status = RCU_KTHREAD_WAITING;
+                rcu_wait(atomic_read(&rnp->wakemask) != 0);
+                rnp->node_kthread_status = RCU_KTHREAD_RUNNING;
+                raw_spin_lock_irqsave(&rnp->lock, flags);
+                mask = atomic_xchg(&rnp->wakemask, 0);
+                rcu_initiate_boost(rnp, flags); /* releases rnp->lock. */
+                for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1) {
+                        if ((mask & 0x1) == 0)
+                                continue;
+                        preempt_disable();
+                        t = per_cpu(rcu_cpu_kthread_task, cpu);
+                        if (!cpu_online(cpu) || t == NULL) {
+                                preempt_enable();
+                                continue;
+                        }
+                        per_cpu(rcu_cpu_has_work, cpu) = 1;
+                        sp.sched_priority = RCU_KTHREAD_PRIO;
+                        sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
+                        preempt_enable();
+                }
+        }
+        /* NOTREACHED */
+        rnp->node_kthread_status = RCU_KTHREAD_STOPPED;
+        return 0;
+}
+
+/*
+ * Set the per-rcu_node kthread's affinity to cover all CPUs that are
+ * served by the rcu_node in question.  The CPU hotplug lock is still
+ * held, so the value of rnp->qsmaskinit will be stable.
+ *
+ * We don't include outgoingcpu in the affinity set, use -1 if there is
+ * no outgoing CPU.  If there are no CPUs left in the affinity set,
+ * this function allows the kthread to execute on any CPU.
+ */
+static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
+{
+        cpumask_var_t cm;
+        int cpu;
+        unsigned long mask = rnp->qsmaskinit;
+
+        if (rnp->node_kthread_task == NULL)
+                return;
+        if (!alloc_cpumask_var(&cm, GFP_KERNEL))
+                return;
+        cpumask_clear(cm);
+        for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1)
+                if ((mask & 0x1) && cpu != outgoingcpu)
+                        cpumask_set_cpu(cpu, cm);
+        if (cpumask_weight(cm) == 0) {
+                cpumask_setall(cm);
+                for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++)
+                        cpumask_clear_cpu(cpu, cm);
+                WARN_ON_ONCE(cpumask_weight(cm) == 0);
+        }
+        set_cpus_allowed_ptr(rnp->node_kthread_task, cm);
+        rcu_boost_kthread_setaffinity(rnp, cm);
+        free_cpumask_var(cm);
+}
+
+/*
+ * Spawn a per-rcu_node kthread, setting priority and affinity.
+ * Called during boot before online/offline can happen, or, if
+ * during runtime, with the main CPU-hotplug locks held.  So only
+ * one of these can be executing at a time.
+ */
+static int __cpuinit rcu_spawn_one_node_kthread(struct rcu_state *rsp,
+                                                struct rcu_node *rnp)
+{
+        unsigned long flags;
+        int rnp_index = rnp - &rsp->node[0];
+        struct sched_param sp;
+        struct task_struct *t;
+
+        if (!rcu_kthreads_spawnable ||
+            rnp->qsmaskinit == 0)
+                return 0;
+        if (rnp->node_kthread_task == NULL) {
+                t = kthread_create(rcu_node_kthread, (void *)rnp,
+                                   "rcun%d", rnp_index);
+                if (IS_ERR(t))
+                        return PTR_ERR(t);
+                raw_spin_lock_irqsave(&rnp->lock, flags);
+                rnp->node_kthread_task = t;
+                raw_spin_unlock_irqrestore(&rnp->lock, flags);
+                sp.sched_priority = 99;
+                sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
+                wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
+        }
+        return rcu_spawn_one_boost_kthread(rsp, rnp, rnp_index);
+}
+
+/*
+ * Spawn all kthreads -- called as soon as the scheduler is running.
+ */
+static int __init rcu_spawn_kthreads(void)
+{
+        int cpu;
+        struct rcu_node *rnp;
+
+        rcu_kthreads_spawnable = 1;
+        for_each_possible_cpu(cpu) {
+                per_cpu(rcu_cpu_has_work, cpu) = 0;
+                if (cpu_online(cpu))
+                        (void)rcu_spawn_one_cpu_kthread(cpu);
+        }
+        rnp = rcu_get_root(rcu_state);
+        (void)rcu_spawn_one_node_kthread(rcu_state, rnp);
+        if (NUM_RCU_NODES > 1) {
+                rcu_for_each_leaf_node(rcu_state, rnp)
+                        (void)rcu_spawn_one_node_kthread(rcu_state, rnp);
+        }
+        return 0;
+}
+early_initcall(rcu_spawn_kthreads);
+
+static void __cpuinit rcu_prepare_kthreads(int cpu)
+{
+        struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
+        struct rcu_node *rnp = rdp->mynode;
+
+        /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
+        if (rcu_kthreads_spawnable) {
+                (void)rcu_spawn_one_cpu_kthread(cpu);
+                if (rnp->node_kthread_task == NULL)
+                        (void)rcu_spawn_one_node_kthread(rcu_state, rnp);
+        }
 }
 
 #else /* #ifdef CONFIG_RCU_BOOST */
@@ -1315,23 +1701,32 @@ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
         raw_spin_unlock_irqrestore(&rnp->lock, flags);
 }
 
-static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp,
-                                          cpumask_var_t cm)
+static void invoke_rcu_callbacks_kthread(void)
 {
+        WARN_ON_ONCE(1);
 }
 
 static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
 {
 }
 
-static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
-                                                 struct rcu_node *rnp,
-                                                 int rnp_index)
+#ifdef CONFIG_HOTPLUG_CPU
+
+static void rcu_stop_cpu_kthread(int cpu)
+{
+}
+
+#endif /* #ifdef CONFIG_HOTPLUG_CPU */
+
+static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
+{
+}
+
+static void rcu_cpu_kthread_setrt(int cpu, int to_rt)
 {
-        return 0;
 }
 
-static void __cpuinit rcu_wake_one_boost_kthread(struct rcu_node *rnp)
+static void __cpuinit rcu_prepare_kthreads(int cpu)
 {
 }
 
@@ -1509,7 +1904,7 @@ static DEFINE_PER_CPU(unsigned long, rcu_dyntick_holdoff);
  *
  * Because it is not legal to invoke rcu_process_callbacks() with irqs
  * disabled, we do one pass of force_quiescent_state(), then do a
- * invoke_rcu_cpu_kthread() to cause rcu_process_callbacks() to be invoked
+ * invoke_rcu_core() to cause rcu_process_callbacks() to be invoked
  * later.  The per-cpu rcu_dyntick_drain variable controls the sequencing.
  */
 int rcu_needs_cpu(int cpu)
@@ -1560,7 +1955,7 @@ int rcu_needs_cpu(int cpu)
 
         /* If RCU callbacks are still pending, RCU still needs this CPU. */
         if (c)
-                invoke_rcu_cpu_kthread();
+                invoke_rcu_core();
         return c;
 }
 
diff --git a/kernel/rcutree_trace.c b/kernel/rcutree_trace.c
index 9678cc3650f5..4e144876dc68 100644
--- a/kernel/rcutree_trace.c
+++ b/kernel/rcutree_trace.c
@@ -46,6 +46,8 @@
 #define RCU_TREE_NONCORE
 #include "rcutree.h"
 
+#ifdef CONFIG_RCU_BOOST
+
 DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
 DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_cpu);
 DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
@@ -58,6 +60,8 @@ static char convert_kthread_status(unsigned int kthread_status)
         return "SRWOY"[kthread_status];
 }
 
+#endif /* #ifdef CONFIG_RCU_BOOST */
+
 static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp)
 {
         if (!rdp->beenonline)
@@ -76,7 +80,7 @@ static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp)
                    rdp->dynticks_fqs);
 #endif /* #ifdef CONFIG_NO_HZ */
         seq_printf(m, " of=%lu ri=%lu", rdp->offline_fqs, rdp->resched_ipi);
-        seq_printf(m, " ql=%ld qs=%c%c%c%c kt=%d/%c/%d ktl=%x b=%ld",
+        seq_printf(m, " ql=%ld qs=%c%c%c%c",
                    rdp->qlen,
                    ".N"[rdp->nxttail[RCU_NEXT_READY_TAIL] !=
                         rdp->nxttail[RCU_NEXT_TAIL]],
@@ -84,13 +88,16 @@ static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp)
                         rdp->nxttail[RCU_NEXT_READY_TAIL]],
                    ".W"[rdp->nxttail[RCU_DONE_TAIL] !=
                         rdp->nxttail[RCU_WAIT_TAIL]],
-                   ".D"[&rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL]],
+                   ".D"[&rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL]]);
+#ifdef CONFIG_RCU_BOOST
+        seq_printf(m, " kt=%d/%c/%d ktl=%x",
                    per_cpu(rcu_cpu_has_work, rdp->cpu),
                    convert_kthread_status(per_cpu(rcu_cpu_kthread_status,
                                           rdp->cpu)),
                    per_cpu(rcu_cpu_kthread_cpu, rdp->cpu),
-                   per_cpu(rcu_cpu_kthread_loops, rdp->cpu) & 0xffff,
-                   rdp->blimit);
+                   per_cpu(rcu_cpu_kthread_loops, rdp->cpu) & 0xffff);
+#endif /* #ifdef CONFIG_RCU_BOOST */
+        seq_printf(m, " b=%ld", rdp->blimit);
         seq_printf(m, " ci=%lu co=%lu ca=%lu\n",
                    rdp->n_cbs_invoked, rdp->n_cbs_orphaned, rdp->n_cbs_adopted);
 }
@@ -147,18 +154,21 @@ static void print_one_rcu_data_csv(struct seq_file *m, struct rcu_data *rdp)
                    rdp->dynticks_fqs);
 #endif /* #ifdef CONFIG_NO_HZ */
         seq_printf(m, ",%lu,%lu", rdp->offline_fqs, rdp->resched_ipi);
-        seq_printf(m, ",%ld,\"%c%c%c%c\",%d,\"%c\",%ld", rdp->qlen,
+        seq_printf(m, ",%ld,\"%c%c%c%c\"", rdp->qlen,
                    ".N"[rdp->nxttail[RCU_NEXT_READY_TAIL] !=
                         rdp->nxttail[RCU_NEXT_TAIL]],
                    ".R"[rdp->nxttail[RCU_WAIT_TAIL] !=
                         rdp->nxttail[RCU_NEXT_READY_TAIL]],
                    ".W"[rdp->nxttail[RCU_DONE_TAIL] !=
                         rdp->nxttail[RCU_WAIT_TAIL]],
-                   ".D"[&rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL]],
+                   ".D"[&rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL]]);
+#ifdef CONFIG_RCU_BOOST
+        seq_printf(m, ",%d,\"%c\"",
                    per_cpu(rcu_cpu_has_work, rdp->cpu),
                    convert_kthread_status(per_cpu(rcu_cpu_kthread_status,
-                                          rdp->cpu)),
-                   rdp->blimit);
+                                          rdp->cpu)));
+#endif /* #ifdef CONFIG_RCU_BOOST */
+        seq_printf(m, ",%ld", rdp->blimit);
         seq_printf(m, ",%lu,%lu,%lu\n",
                    rdp->n_cbs_invoked, rdp->n_cbs_orphaned, rdp->n_cbs_adopted);
 }
@@ -169,7 +179,11 @@ static int show_rcudata_csv(struct seq_file *m, void *unused)
 #ifdef CONFIG_NO_HZ
         seq_puts(m, "\"dt\",\"dt nesting\",\"dt NMI nesting\",\"df\",");
 #endif /* #ifdef CONFIG_NO_HZ */
-        seq_puts(m, "\"of\",\"ri\",\"ql\",\"b\",\"ci\",\"co\",\"ca\"\n");
+        seq_puts(m, "\"of\",\"ri\",\"ql\",\"qs\"");
+#ifdef CONFIG_RCU_BOOST
+        seq_puts(m, "\"kt\",\"ktl\"");
+#endif /* #ifdef CONFIG_RCU_BOOST */
+        seq_puts(m, ",\"b\",\"ci\",\"co\",\"ca\"\n");
 #ifdef CONFIG_TREE_PREEMPT_RCU
         seq_puts(m, "\"rcu_preempt:\"\n");
         PRINT_RCU_DATA(rcu_preempt_data, print_one_rcu_data_csv, m);
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 13960170cad4..40cf63ddd4b3 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -58,7 +58,7 @@ DEFINE_PER_CPU(struct task_struct *, ksoftirqd);
 
 char *softirq_to_name[NR_SOFTIRQS] = {
         "HI", "TIMER", "NET_TX", "NET_RX", "BLOCK", "BLOCK_IOPOLL",
-        "TASKLET", "SCHED", "HRTIMER"
+        "TASKLET", "SCHED", "HRTIMER", "RCU"
 };
 
 /*