hung_task: fix false positive during vfork
[linux-2.6.git] / kernel / rcutree.c
index 2c07adb..ba06207 100644 (file)
@@ -36,7 +36,7 @@
 #include <linux/interrupt.h>
 #include <linux/sched.h>
 #include <linux/nmi.h>
-#include <asm/atomic.h>
+#include <linux/atomic.h>
 #include <linux/bitops.h>
 #include <linux/module.h>
 #include <linux/completion.h>
@@ -49,6 +49,7 @@
 #include <linux/kernel_stat.h>
 #include <linux/wait.h>
 #include <linux/kthread.h>
+#include <linux/prefetch.h>
 
 #include "rcutree.h"
 
@@ -83,10 +84,35 @@ DEFINE_PER_CPU(struct rcu_data, rcu_bh_data);
 
 static struct rcu_state *rcu_state;
 
+/*
+ * The rcu_scheduler_active variable transitions from zero to one just
+ * before the first task is spawned.  So when this variable is zero, RCU
+ * can assume that there is but one task, allowing RCU to (for example)
+ * optimized synchronize_sched() to a simple barrier().  When this variable
+ * is one, RCU must actually do all the hard work required to detect real
+ * grace periods.  This variable is also used to suppress boot-time false
+ * positives from lockdep-RCU error checking.
+ */
 int rcu_scheduler_active __read_mostly;
 EXPORT_SYMBOL_GPL(rcu_scheduler_active);
 
 /*
+ * The rcu_scheduler_fully_active variable transitions from zero to one
+ * during the early_initcall() processing, which is after the scheduler
+ * is capable of creating new tasks.  So RCU processing (for example,
+ * creating tasks for RCU priority boosting) must be delayed until after
+ * rcu_scheduler_fully_active transitions from zero to one.  We also
+ * currently delay invocation of any RCU callbacks until after this point.
+ *
+ * It might later prove better for people registering RCU callbacks during
+ * early boot to take responsibility for these callbacks, but one step at
+ * a time.
+ */
+static int rcu_scheduler_fully_active __read_mostly;
+
+#ifdef CONFIG_RCU_BOOST
+
+/*
  * Control variables for per-CPU and per-rcu_node kthreads.  These
  * handle all flavors of RCU.
  */
@@ -94,12 +120,13 @@ static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task);
 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
 DEFINE_PER_CPU(int, rcu_cpu_kthread_cpu);
 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
-static DEFINE_PER_CPU(wait_queue_head_t, rcu_cpu_wq);
 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. */
 
@@ -157,6 +184,7 @@ void rcu_note_context_switch(int cpu)
        rcu_sched_qs(cpu);
        rcu_preempt_note_context_switch(cpu);
 }
+EXPORT_SYMBOL_GPL(rcu_note_context_switch);
 
 #ifdef CONFIG_NO_HZ
 DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
@@ -581,21 +609,24 @@ static void print_cpu_stall(struct rcu_state *rsp)
 
 static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
 {
-       long delta;
+       unsigned long j;
+       unsigned long js;
        struct rcu_node *rnp;
 
        if (rcu_cpu_stall_suppress)
                return;
-       delta = jiffies - ACCESS_ONCE(rsp->jiffies_stall);
+       j = ACCESS_ONCE(jiffies);
+       js = ACCESS_ONCE(rsp->jiffies_stall);
        rnp = rdp->mynode;
-       if ((ACCESS_ONCE(rnp->qsmask) & rdp->grpmask) && delta >= 0) {
+       if ((ACCESS_ONCE(rnp->qsmask) & rdp->grpmask) && ULONG_CMP_GE(j, js)) {
 
                /* We haven't checked in, so go dump stack. */
                print_cpu_stall(rsp);
 
-       } else if (rcu_gp_in_progress(rsp) && delta >= RCU_STALL_RAT_DELAY) {
+       } else if (rcu_gp_in_progress(rsp) &&
+                  ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY)) {
 
-               /* They had two time units to dump stack, so complain. */
+               /* They had a few time units to dump stack, so complain. */
                print_other_cpu_stall(rsp);
        }
 }
@@ -1084,14 +1115,8 @@ 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);
@@ -1129,22 +1154,7 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
                raw_spin_unlock_irqrestore(&rnp->lock, flags);
        if (need_report & RCU_OFL_TASKS_EXP_GP)
                rcu_report_exp_rnp(rsp, rnp);
-
-       /*
-        * If there are no more online CPUs for this rcu_node structure,
-        * kill the rcu_node structure's kthread.  Otherwise, adjust its
-        * affinity.
-        */
-       t = rnp->node_kthread_task;
-       if (t != NULL &&
-           rnp->qsmaskinit == 0) {
-               raw_spin_lock_irqsave(&rnp->lock, flags);
-               rnp->node_kthread_task = NULL;
-               raw_spin_unlock_irqrestore(&rnp->lock, flags);
-               kthread_stop(t);
-               rcu_stop_boost_kthread(rnp);
-       } else
-               rcu_node_kthread_setaffinity(rnp, -1);
+       rcu_node_kthread_setaffinity(rnp, -1);
 }
 
 /*
@@ -1242,7 +1252,7 @@ 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();
 }
 
 /*
@@ -1288,7 +1298,7 @@ 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
@@ -1316,8 +1326,7 @@ static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *))
                        return;
                }
                if (rnp->qsmask == 0) {
-                       rcu_initiate_boost(rnp);
-                       raw_spin_unlock_irqrestore(&rnp->lock, flags);
+                       rcu_initiate_boost(rnp, flags); /* releases rnp->lock */
                        continue;
                }
                cpu = rnp->grplo;
@@ -1336,10 +1345,10 @@ static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *))
                raw_spin_unlock_irqrestore(&rnp->lock, flags);
        }
        rnp = rcu_get_root(rsp);
-       raw_spin_lock_irqsave(&rnp->lock, flags);
-       if (rnp->qsmask == 0)
-               rcu_initiate_boost(rnp);
-       raw_spin_unlock_irqrestore(&rnp->lock, flags);
+       if (rnp->qsmask == 0) {
+               raw_spin_lock_irqsave(&rnp->lock, flags);
+               rcu_initiate_boost(rnp, flags); /* releases rnp->lock. */
+       }
 }
 
 /*
@@ -1454,13 +1463,14 @@ __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));
@@ -1477,342 +1487,22 @@ 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)
+static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
 {
-       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);
+       if (unlikely(!ACCESS_ONCE(rcu_scheduler_fully_active)))
                return;
-       }
-       wake_up(&__get_cpu_var(rcu_cpu_wq));
-       local_irq_restore(flags);
-}
-
-/*
- * Wake up the specified per-rcu_node-structure kthread.
- * The caller must hold ->lock.
- */
-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)
+       if (likely(!rsp->boost)) {
+               rcu_do_batch(rsp, rdp);
                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)
-{
-       unsigned long flags;
-       struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, arg);
-       struct rcu_node *rnp = rdp->mynode;
-
-       raw_spin_lock_irqsave(&rnp->lock, flags);
-       rnp->wakemask |= rdp->grpmask;
-       invoke_rcu_node_kthread(rnp);
-       raw_spin_unlock_irqrestore(&rnp->lock, flags);
+       invoke_rcu_callbacks_kthread();
 }
 
-/*
- * 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)
+static void invoke_rcu_core(void)
 {
-       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);
-       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;
+       raise_softirq(RCU_SOFTIRQ);
 }
 
-/*
- * 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);
-       wait_queue_head_t *wqp = &per_cpu(rcu_cpu_wq, cpu);
-       char work;
-       char *workp = &per_cpu(rcu_cpu_has_work, cpu);
-
-       for (;;) {
-               *statusp = RCU_KTHREAD_WAITING;
-               wait_event_interruptible(*wqp,
-                                        *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)
-{
-       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;
-       wake_up_process(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;
-               wait_event_interruptible(rnp->node_wq, rnp->wakemask != 0 ||
-                                                      kthread_should_stop());
-               if (kthread_should_stop())
-                       break;
-               rnp->node_kthread_status = RCU_KTHREAD_RUNNING;
-               raw_spin_lock_irqsave(&rnp->lock, flags);
-               mask = rnp->wakemask;
-               rnp->wakemask = 0;
-               rcu_initiate_boost(rnp);
-               raw_spin_unlock_irqrestore(&rnp->lock, flags);
-               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();
-               }
-       }
-       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 || mask == 0)
-               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);
-               wake_up_process(t);
-               sp.sched_priority = 99;
-               sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
-       }
-       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) {
-               init_waitqueue_head(&per_cpu(rcu_cpu_wq, 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);
-       init_waitqueue_head(&rnp->node_wq);
-       rcu_init_boost_waitqueue(rnp);
-       (void)rcu_spawn_one_node_kthread(rcu_state, rnp);
-       if (NUM_RCU_NODES > 1)
-               rcu_for_each_leaf_node(rcu_state, rnp) {
-                       init_waitqueue_head(&rnp->node_wq);
-                       rcu_init_boost_waitqueue(rnp);
-                       (void)rcu_spawn_one_node_kthread(rcu_state, 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)
@@ -1838,6 +1528,13 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
        /* Add the callback to our list. */
        *rdp->nxttail[RCU_NEXT_TAIL] = head;
        rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
+       rdp->qlen++;
+
+       /* If interrupts were disabled, don't dive into RCU core. */
+       if (irqs_disabled_flags(flags)) {
+               local_irq_restore(flags);
+               return;
+       }
 
        /*
         * Force the grace period if too many callbacks or too long waiting.
@@ -1846,7 +1543,7 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
         * invoking force_quiescent_state() if the newly enqueued callback
         * is the only one waiting for a grace period to complete.
         */
-       if (unlikely(++rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) {
+       if (unlikely(rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) {
 
                /* Are we ignoring a completed grace period? */
                rcu_process_gp_end(rsp, rdp);
@@ -2205,26 +1902,13 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptible)
        raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
 }
 
-static void __cpuinit rcu_online_cpu(int cpu)
+static void __cpuinit rcu_prepare_cpu(int cpu)
 {
        rcu_init_percpu_data(cpu, &rcu_sched_state, 0);
        rcu_init_percpu_data(cpu, &rcu_bh_state, 0);
        rcu_preempt_init_percpu_data(cpu);
 }
 
-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;
-
-       /* 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);
-       }
-}
-
 /*
  * Handle CPU online/offline notification events.
  */
@@ -2238,8 +1922,8 @@ static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
        switch (action) {
        case CPU_UP_PREPARE:
        case CPU_UP_PREPARE_FROZEN:
-               rcu_online_cpu(cpu);
-               rcu_online_kthreads(cpu);
+               rcu_prepare_cpu(cpu);
+               rcu_prepare_kthreads(cpu);
                break;
        case CPU_ONLINE:
        case CPU_DOWN_FAILED:
@@ -2389,6 +2073,7 @@ 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