1 files changed, 43 insertions, 379 deletions

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 89419ff92e99..ba06207b1dd3 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -84,10 +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.
  */
@@ -96,10 +121,12 @@ 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);
 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 +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);
@@ -1231,7 +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();
 }
 
 /*
@@ -1277,7 +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
@@ -1442,13 +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));
@@ -1465,342 +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)
-{
-        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)
-{
-        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)
+static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
 {
-        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)
+        if (unlikely(!ACCESS_ONCE(rcu_scheduler_fully_active)))
                 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 +1909,6 @@ 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 +1926,6 @@ 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 +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