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

Pull RCU changes from Ingo Molnar:

 0. 'idle RCU':

     Adds RCU APIs that allow non-idle tasks to enter RCU idle mode and
     provides x86 code to make use of them, allowing RCU to treat
     user-mode execution as an extended quiescent state when the new
     RCU_USER_QS kernel configuration parameter is specified.  (Work is
     in progress to port this to a few other architectures, but is not
     part of this series.)

 1.  A fix for a latent bug that has been in RCU ever since the addition
     of CPU stall warnings.  This bug results in false-positive stall
     warnings, but thus far only on embedded systems with severely
     cut-down userspace configurations.

 2.  Further reductions in latency spikes for huge systems, along with
     additional boot-time adaptation to the actual hardware.

     This is a large change, as it moves RCU grace-period initialization
     and cleanup, along with quiescent-state forcing, from softirq to a
     kthread.  However, it appears to be in quite good shape (famous
     last words).

 3.  Updates to documentation and rcutorture, the latter category
     including keeping statistics on CPU-hotplug latencies and fixing
     some initialization-time races.

 4.  CPU-hotplug fixes and improvements.

 5.  Idle-loop fixes that were omitted on an earlier submission.

 6.  Miscellaneous fixes and improvements

In certain RCU configurations new kernel threads will show up (rcu_bh,
rcu_sched), showing RCU processing overhead.

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (90 commits)
  rcu: Apply micro-optimization and int/bool fixes to RCU's idle handling
  rcu: Userspace RCU extended QS selftest
  x86: Exit RCU extended QS on notify resume
  x86: Use the new schedule_user API on userspace preemption
  rcu: Exit RCU extended QS on user preemption
  rcu: Exit RCU extended QS on kernel preemption after irq/exception
  x86: Exception hooks for userspace RCU extended QS
  x86: Unspaghettize do_general_protection()
  x86: Syscall hooks for userspace RCU extended QS
  rcu: Switch task's syscall hooks on context switch
  rcu: Ignore userspace extended quiescent state by default
  rcu: Allow rcu_user_enter()/exit() to nest
  rcu: Settle config for userspace extended quiescent state
  rcu: Make RCU_FAST_NO_HZ handle adaptive ticks
  rcu: New rcu_user_enter_after_irq() and rcu_user_exit_after_irq() APIs
  rcu: New rcu_user_enter() and rcu_user_exit() APIs
  ia64: Add missing RCU idle APIs on idle loop
  xtensa: Add missing RCU idle APIs on idle loop
  score: Add missing RCU idle APIs on idle loop
  parisc: Add missing RCU idle APIs on idle loop
  ...

1 files changed, 27 insertions, 84 deletions

diff --git a/kernel/softirq.c b/kernel/softirq.c
index b73e681df09e..5c6a5bd8462f 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -23,6 +23,7 @@
 #include <linux/rcupdate.h>
 #include <linux/ftrace.h>
 #include <linux/smp.h>
+#include <linux/smpboot.h>
 #include <linux/tick.h>
 
 #define CREATE_TRACE_POINTS
@@ -742,49 +743,22 @@ void __init softirq_init(void)
 	open_softirq(HI_SOFTIRQ, tasklet_hi_action);
 }
 
-static int run_ksoftirqd(void * __bind_cpu)
+static int ksoftirqd_should_run(unsigned int cpu)
 {
-	set_current_state(TASK_INTERRUPTIBLE);
-
-	while (!kthread_should_stop()) {
-		preempt_disable();
-		if (!local_softirq_pending()) {
-			schedule_preempt_disabled();
-		}
-
-		__set_current_state(TASK_RUNNING);
-
-		while (local_softirq_pending()) {
-			/* Preempt disable stops cpu going offline.
-			   If already offline, we'll be on wrong CPU:
-			   don't process */
-			if (cpu_is_offline((long)__bind_cpu))
-				goto wait_to_die;
-			local_irq_disable();
-			if (local_softirq_pending())
-				__do_softirq();
-			local_irq_enable();
-			sched_preempt_enable_no_resched();
-			cond_resched();
-			preempt_disable();
-			rcu_note_context_switch((long)__bind_cpu);
-		}
-		preempt_enable();
-		set_current_state(TASK_INTERRUPTIBLE);
-	}
-	__set_current_state(TASK_RUNNING);
-	return 0;
+	return local_softirq_pending();
+}
 
-wait_to_die:
-	preempt_enable();
-	/* Wait for kthread_stop */
-	set_current_state(TASK_INTERRUPTIBLE);
-	while (!kthread_should_stop()) {
-		schedule();
-		set_current_state(TASK_INTERRUPTIBLE);
+static void run_ksoftirqd(unsigned int cpu)
+{
+	local_irq_disable();
+	if (local_softirq_pending()) {
+		__do_softirq();
+		rcu_note_context_switch(cpu);
+		local_irq_enable();
+		cond_resched();
+		return;
 	}
-	__set_current_state(TASK_RUNNING);
-	return 0;
+	local_irq_enable();
 }
 
 #ifdef CONFIG_HOTPLUG_CPU
@@ -850,50 +824,14 @@ static int __cpuinit cpu_callback(struct notifier_block *nfb,
 				  unsigned long action,
 				  void *hcpu)
 {
-	int hotcpu = (unsigned long)hcpu;
-	struct task_struct *p;
-
 	switch (action) {
-	case CPU_UP_PREPARE:
-	case CPU_UP_PREPARE_FROZEN:
-		p = kthread_create_on_node(run_ksoftirqd,
-					   hcpu,
-					   cpu_to_node(hotcpu),
-					   "ksoftirqd/%d", hotcpu);
-		if (IS_ERR(p)) {
-			printk("ksoftirqd for %i failed\n", hotcpu);
-			return notifier_from_errno(PTR_ERR(p));
-		}
-		kthread_bind(p, hotcpu);
-  		per_cpu(ksoftirqd, hotcpu) = p;
- 		break;
-	case CPU_ONLINE:
-	case CPU_ONLINE_FROZEN:
-		wake_up_process(per_cpu(ksoftirqd, hotcpu));
-		break;
 #ifdef CONFIG_HOTPLUG_CPU
-	case CPU_UP_CANCELED:
-	case CPU_UP_CANCELED_FROZEN:
-		if (!per_cpu(ksoftirqd, hotcpu))
-			break;
-		/* Unbind so it can run.  Fall thru. */
-		kthread_bind(per_cpu(ksoftirqd, hotcpu),
-			     cpumask_any(cpu_online_mask));
 	case CPU_DEAD:
-	case CPU_DEAD_FROZEN: {
-		static const struct sched_param param = {
-			.sched_priority = MAX_RT_PRIO-1
-		};
-
-		p = per_cpu(ksoftirqd, hotcpu);
-		per_cpu(ksoftirqd, hotcpu) = NULL;
-		sched_setscheduler_nocheck(p, SCHED_FIFO, &param);
-		kthread_stop(p);
-		takeover_tasklets(hotcpu);
+	case CPU_DEAD_FROZEN:
+		takeover_tasklets((unsigned long)hcpu);
 		break;
-	}
 #endif /* CONFIG_HOTPLUG_CPU */
- 	}
+	}
 	return NOTIFY_OK;
 }
 
@@ -901,14 +839,19 @@ static struct notifier_block __cpuinitdata cpu_nfb = {
 	.notifier_call = cpu_callback
 };
 
+static struct smp_hotplug_thread softirq_threads = {
+	.store			= &ksoftirqd,
+	.thread_should_run	= ksoftirqd_should_run,
+	.thread_fn		= run_ksoftirqd,
+	.thread_comm		= "ksoftirqd/%u",
+};
+
 static __init int spawn_ksoftirqd(void)
 {
-	void *cpu = (void *)(long)smp_processor_id();
-	int err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
-
-	BUG_ON(err != NOTIFY_OK);
-	cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
 	register_cpu_notifier(&cpu_nfb);
+
+	BUG_ON(smpboot_register_percpu_thread(&softirq_threads));
+
 	return 0;
 }
 early_initcall(spawn_ksoftirqd);