X-Git-Url: http://ftp.safe.ca/?a=blobdiff_plain;f=kernel%2Fstop_machine.c;h=b4e7431e7c78996607ef0495d7cb50bc34621d2c;hb=b8ae30ee26d379db436b0b8c8c3ff1b52f69e5d1;hp=b7350bbfb076293dd6d13d7ba060b3aba1f673a9;hpb=3401a61e16a5b852d4e353c8850c857105a67a9c;p=safe%2Fjmp%2Flinux-2.6

diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index b7350bb..b4e7431 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -1,215 +1,486 @@
-/* Copyright 2005 Rusty Russell rusty@rustcorp.com.au IBM Corporation.
- * GPL v2 and any later version.
+/*
+ * kernel/stop_machine.c
+ *
+ * Copyright (C) 2008, 2005	IBM Corporation.
+ * Copyright (C) 2008, 2005	Rusty Russell rusty@rustcorp.com.au
+ * Copyright (C) 2010		SUSE Linux Products GmbH
+ * Copyright (C) 2010		Tejun Heo <tj@kernel.org>
+ *
+ * This file is released under the GPLv2 and any later version.
  */
+#include <linux/completion.h>
 #include <linux/cpu.h>
-#include <linux/err.h>
+#include <linux/init.h>
 #include <linux/kthread.h>
 #include <linux/module.h>
+#include <linux/percpu.h>
 #include <linux/sched.h>
 #include <linux/stop_machine.h>
-#include <linux/syscalls.h>
 #include <linux/interrupt.h>
+#include <linux/kallsyms.h>
 
 #include <asm/atomic.h>
-#include <asm/uaccess.h>
 
-/* Since we effect priority and affinity (both of which are visible
- * to, and settable by outside processes) we do indirection via a
- * kthread. */
+/*
+ * Structure to determine completion condition and record errors.  May
+ * be shared by works on different cpus.
+ */
+struct cpu_stop_done {
+	atomic_t		nr_todo;	/* nr left to execute */
+	bool			executed;	/* actually executed? */
+	int			ret;		/* collected return value */
+	struct completion	completion;	/* fired if nr_todo reaches 0 */
+};
 
-/* Thread to stop each CPU in user context. */
-enum stopmachine_state {
-	STOPMACHINE_WAIT,
-	STOPMACHINE_PREPARE,
-	STOPMACHINE_DISABLE_IRQ,
-	STOPMACHINE_EXIT,
+/* the actual stopper, one per every possible cpu, enabled on online cpus */
+struct cpu_stopper {
+	spinlock_t		lock;
+	struct list_head	works;		/* list of pending works */
+	struct task_struct	*thread;	/* stopper thread */
+	bool			enabled;	/* is this stopper enabled? */
 };
 
-static enum stopmachine_state stopmachine_state;
-static unsigned int stopmachine_num_threads;
-static atomic_t stopmachine_thread_ack;
+static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper);
 
-static int stopmachine(void *cpu)
+static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo)
 {
-	int irqs_disabled = 0;
-	int prepared = 0;
+	memset(done, 0, sizeof(*done));
+	atomic_set(&done->nr_todo, nr_todo);
+	init_completion(&done->completion);
+}
 
-	set_cpus_allowed_ptr(current, &cpumask_of_cpu((int)(long)cpu));
+/* signal completion unless @done is NULL */
+static void cpu_stop_signal_done(struct cpu_stop_done *done, bool executed)
+{
+	if (done) {
+		if (executed)
+			done->executed = true;
+		if (atomic_dec_and_test(&done->nr_todo))
+			complete(&done->completion);
+	}
+}
 
-	/* Ack: we are alive */
-	smp_mb(); /* Theoretically the ack = 0 might not be on this CPU yet. */
-	atomic_inc(&stopmachine_thread_ack);
+/* queue @work to @stopper.  if offline, @work is completed immediately */
+static void cpu_stop_queue_work(struct cpu_stopper *stopper,
+				struct cpu_stop_work *work)
+{
+	unsigned long flags;
 
-	/* Simple state machine */
-	while (stopmachine_state != STOPMACHINE_EXIT) {
-		if (stopmachine_state == STOPMACHINE_DISABLE_IRQ 
-		    && !irqs_disabled) {
-			local_irq_disable();
-			hard_irq_disable();
-			irqs_disabled = 1;
-			/* Ack: irqs disabled. */
-			smp_mb(); /* Must read state first. */
-			atomic_inc(&stopmachine_thread_ack);
-		} else if (stopmachine_state == STOPMACHINE_PREPARE
-			   && !prepared) {
-			/* Everyone is in place, hold CPU. */
-			preempt_disable();
-			prepared = 1;
-			smp_mb(); /* Must read state first. */
-			atomic_inc(&stopmachine_thread_ack);
-		}
-		/* Yield in first stage: migration threads need to
-		 * help our sisters onto their CPUs. */
-		if (!prepared && !irqs_disabled)
-			yield();
-		cpu_relax();
+	spin_lock_irqsave(&stopper->lock, flags);
+
+	if (stopper->enabled) {
+		list_add_tail(&work->list, &stopper->works);
+		wake_up_process(stopper->thread);
+	} else
+		cpu_stop_signal_done(work->done, false);
+
+	spin_unlock_irqrestore(&stopper->lock, flags);
+}
+
+/**
+ * stop_one_cpu - stop a cpu
+ * @cpu: cpu to stop
+ * @fn: function to execute
+ * @arg: argument to @fn
+ *
+ * Execute @fn(@arg) on @cpu.  @fn is run in a process context with
+ * the highest priority preempting any task on the cpu and
+ * monopolizing it.  This function returns after the execution is
+ * complete.
+ *
+ * This function doesn't guarantee @cpu stays online till @fn
+ * completes.  If @cpu goes down in the middle, execution may happen
+ * partially or fully on different cpus.  @fn should either be ready
+ * for that or the caller should ensure that @cpu stays online until
+ * this function completes.
+ *
+ * CONTEXT:
+ * Might sleep.
+ *
+ * RETURNS:
+ * -ENOENT if @fn(@arg) was not executed because @cpu was offline;
+ * otherwise, the return value of @fn.
+ */
+int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg)
+{
+	struct cpu_stop_done done;
+	struct cpu_stop_work work = { .fn = fn, .arg = arg, .done = &done };
+
+	cpu_stop_init_done(&done, 1);
+	cpu_stop_queue_work(&per_cpu(cpu_stopper, cpu), &work);
+	wait_for_completion(&done.completion);
+	return done.executed ? done.ret : -ENOENT;
+}
+
+/**
+ * stop_one_cpu_nowait - stop a cpu but don't wait for completion
+ * @cpu: cpu to stop
+ * @fn: function to execute
+ * @arg: argument to @fn
+ *
+ * Similar to stop_one_cpu() but doesn't wait for completion.  The
+ * caller is responsible for ensuring @work_buf is currently unused
+ * and will remain untouched until stopper starts executing @fn.
+ *
+ * CONTEXT:
+ * Don't care.
+ */
+void stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
+			struct cpu_stop_work *work_buf)
+{
+	*work_buf = (struct cpu_stop_work){ .fn = fn, .arg = arg, };
+	cpu_stop_queue_work(&per_cpu(cpu_stopper, cpu), work_buf);
+}
+
+/* static data for stop_cpus */
+static DEFINE_MUTEX(stop_cpus_mutex);
+static DEFINE_PER_CPU(struct cpu_stop_work, stop_cpus_work);
+
+int __stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
+{
+	struct cpu_stop_work *work;
+	struct cpu_stop_done done;
+	unsigned int cpu;
+
+	/* initialize works and done */
+	for_each_cpu(cpu, cpumask) {
+		work = &per_cpu(stop_cpus_work, cpu);
+		work->fn = fn;
+		work->arg = arg;
+		work->done = &done;
 	}
+	cpu_stop_init_done(&done, cpumask_weight(cpumask));
 
-	/* Ack: we are exiting. */
-	smp_mb(); /* Must read state first. */
-	atomic_inc(&stopmachine_thread_ack);
+	/*
+	 * Disable preemption while queueing to avoid getting
+	 * preempted by a stopper which might wait for other stoppers
+	 * to enter @fn which can lead to deadlock.
+	 */
+	preempt_disable();
+	for_each_cpu(cpu, cpumask)
+		cpu_stop_queue_work(&per_cpu(cpu_stopper, cpu),
+				    &per_cpu(stop_cpus_work, cpu));
+	preempt_enable();
 
-	if (irqs_disabled)
-		local_irq_enable();
-	if (prepared)
-		preempt_enable();
+	wait_for_completion(&done.completion);
+	return done.executed ? done.ret : -ENOENT;
+}
 
-	return 0;
+/**
+ * stop_cpus - stop multiple cpus
+ * @cpumask: cpus to stop
+ * @fn: function to execute
+ * @arg: argument to @fn
+ *
+ * Execute @fn(@arg) on online cpus in @cpumask.  On each target cpu,
+ * @fn is run in a process context with the highest priority
+ * preempting any task on the cpu and monopolizing it.  This function
+ * returns after all executions are complete.
+ *
+ * This function doesn't guarantee the cpus in @cpumask stay online
+ * till @fn completes.  If some cpus go down in the middle, execution
+ * on the cpu may happen partially or fully on different cpus.  @fn
+ * should either be ready for that or the caller should ensure that
+ * the cpus stay online until this function completes.
+ *
+ * All stop_cpus() calls are serialized making it safe for @fn to wait
+ * for all cpus to start executing it.
+ *
+ * CONTEXT:
+ * Might sleep.
+ *
+ * RETURNS:
+ * -ENOENT if @fn(@arg) was not executed at all because all cpus in
+ * @cpumask were offline; otherwise, 0 if all executions of @fn
+ * returned 0, any non zero return value if any returned non zero.
+ */
+int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
+{
+	int ret;
+
+	/* static works are used, process one request at a time */
+	mutex_lock(&stop_cpus_mutex);
+	ret = __stop_cpus(cpumask, fn, arg);
+	mutex_unlock(&stop_cpus_mutex);
+	return ret;
 }
 
-/* Change the thread state */
-static void stopmachine_set_state(enum stopmachine_state state)
+/**
+ * try_stop_cpus - try to stop multiple cpus
+ * @cpumask: cpus to stop
+ * @fn: function to execute
+ * @arg: argument to @fn
+ *
+ * Identical to stop_cpus() except that it fails with -EAGAIN if
+ * someone else is already using the facility.
+ *
+ * CONTEXT:
+ * Might sleep.
+ *
+ * RETURNS:
+ * -EAGAIN if someone else is already stopping cpus, -ENOENT if
+ * @fn(@arg) was not executed at all because all cpus in @cpumask were
+ * offline; otherwise, 0 if all executions of @fn returned 0, any non
+ * zero return value if any returned non zero.
+ */
+int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
 {
-	atomic_set(&stopmachine_thread_ack, 0);
-	smp_wmb();
-	stopmachine_state = state;
-	while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
-		cpu_relax();
+	int ret;
+
+	/* static works are used, process one request at a time */
+	if (!mutex_trylock(&stop_cpus_mutex))
+		return -EAGAIN;
+	ret = __stop_cpus(cpumask, fn, arg);
+	mutex_unlock(&stop_cpus_mutex);
+	return ret;
 }
 
-static int stop_machine(void)
+static int cpu_stopper_thread(void *data)
 {
-	int i, ret = 0;
+	struct cpu_stopper *stopper = data;
+	struct cpu_stop_work *work;
+	int ret;
 
-	atomic_set(&stopmachine_thread_ack, 0);
-	stopmachine_num_threads = 0;
-	stopmachine_state = STOPMACHINE_WAIT;
+repeat:
+	set_current_state(TASK_INTERRUPTIBLE);	/* mb paired w/ kthread_stop */
 
-	for_each_online_cpu(i) {
-		if (i == raw_smp_processor_id())
-			continue;
-		ret = kernel_thread(stopmachine, (void *)(long)i,CLONE_KERNEL);
-		if (ret < 0)
-			break;
-		stopmachine_num_threads++;
+	if (kthread_should_stop()) {
+		__set_current_state(TASK_RUNNING);
+		return 0;
 	}
 
-	/* Wait for them all to come to life. */
-	while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads) {
-		yield();
-		cpu_relax();
+	work = NULL;
+	spin_lock_irq(&stopper->lock);
+	if (!list_empty(&stopper->works)) {
+		work = list_first_entry(&stopper->works,
+					struct cpu_stop_work, list);
+		list_del_init(&work->list);
 	}
+	spin_unlock_irq(&stopper->lock);
 
-	/* If some failed, kill them all. */
-	if (ret < 0) {
-		stopmachine_set_state(STOPMACHINE_EXIT);
-		return ret;
-	}
+	if (work) {
+		cpu_stop_fn_t fn = work->fn;
+		void *arg = work->arg;
+		struct cpu_stop_done *done = work->done;
+		char ksym_buf[KSYM_NAME_LEN];
 
-	/* Now they are all started, make them hold the CPUs, ready. */
-	preempt_disable();
-	stopmachine_set_state(STOPMACHINE_PREPARE);
+		__set_current_state(TASK_RUNNING);
 
-	/* Make them disable irqs. */
-	local_irq_disable();
-	hard_irq_disable();
-	stopmachine_set_state(STOPMACHINE_DISABLE_IRQ);
+		/* cpu stop callbacks are not allowed to sleep */
+		preempt_disable();
 
-	return 0;
+		ret = fn(arg);
+		if (ret)
+			done->ret = ret;
+
+		/* restore preemption and check it's still balanced */
+		preempt_enable();
+		WARN_ONCE(preempt_count(),
+			  "cpu_stop: %s(%p) leaked preempt count\n",
+			  kallsyms_lookup((unsigned long)fn, NULL, NULL, NULL,
+					  ksym_buf), arg);
+
+		cpu_stop_signal_done(done, true);
+	} else
+		schedule();
+
+	goto repeat;
 }
 
-static void restart_machine(void)
+/* manage stopper for a cpu, mostly lifted from sched migration thread mgmt */
+static int __cpuinit cpu_stop_cpu_callback(struct notifier_block *nfb,
+					   unsigned long action, void *hcpu)
 {
-	stopmachine_set_state(STOPMACHINE_EXIT);
-	local_irq_enable();
-	preempt_enable_no_resched();
+	struct sched_param param = { .sched_priority = MAX_RT_PRIO - 1 };
+	unsigned int cpu = (unsigned long)hcpu;
+	struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
+	struct task_struct *p;
+
+	switch (action & ~CPU_TASKS_FROZEN) {
+	case CPU_UP_PREPARE:
+		BUG_ON(stopper->thread || stopper->enabled ||
+		       !list_empty(&stopper->works));
+		p = kthread_create(cpu_stopper_thread, stopper, "migration/%d",
+				   cpu);
+		if (IS_ERR(p))
+			return NOTIFY_BAD;
+		sched_setscheduler_nocheck(p, SCHED_FIFO, &param);
+		get_task_struct(p);
+		stopper->thread = p;
+		break;
+
+	case CPU_ONLINE:
+		kthread_bind(stopper->thread, cpu);
+		/* strictly unnecessary, as first user will wake it */
+		wake_up_process(stopper->thread);
+		/* mark enabled */
+		spin_lock_irq(&stopper->lock);
+		stopper->enabled = true;
+		spin_unlock_irq(&stopper->lock);
+		break;
+
+#ifdef CONFIG_HOTPLUG_CPU
+	case CPU_UP_CANCELED:
+	case CPU_DEAD:
+	{
+		struct cpu_stop_work *work;
+
+		/* kill the stopper */
+		kthread_stop(stopper->thread);
+		/* drain remaining works */
+		spin_lock_irq(&stopper->lock);
+		list_for_each_entry(work, &stopper->works, list)
+			cpu_stop_signal_done(work->done, false);
+		stopper->enabled = false;
+		spin_unlock_irq(&stopper->lock);
+		/* release the stopper */
+		put_task_struct(stopper->thread);
+		stopper->thread = NULL;
+		break;
+	}
+#endif
+	}
+
+	return NOTIFY_OK;
 }
 
-struct stop_machine_data {
-	int (*fn)(void *);
-	void *data;
-	struct completion done;
+/*
+ * Give it a higher priority so that cpu stopper is available to other
+ * cpu notifiers.  It currently shares the same priority as sched
+ * migration_notifier.
+ */
+static struct notifier_block __cpuinitdata cpu_stop_cpu_notifier = {
+	.notifier_call	= cpu_stop_cpu_callback,
+	.priority	= 10,
 };
 
-static int do_stop(void *_smdata)
+static int __init cpu_stop_init(void)
 {
-	struct stop_machine_data *smdata = _smdata;
-	int ret;
+	void *bcpu = (void *)(long)smp_processor_id();
+	unsigned int cpu;
+	int err;
+
+	for_each_possible_cpu(cpu) {
+		struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
 
-	ret = stop_machine();
-	if (ret == 0) {
-		ret = smdata->fn(smdata->data);
-		restart_machine();
+		spin_lock_init(&stopper->lock);
+		INIT_LIST_HEAD(&stopper->works);
 	}
 
-	/* We're done: you can kthread_stop us now */
-	complete(&smdata->done);
+	/* start one for the boot cpu */
+	err = cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_UP_PREPARE,
+				    bcpu);
+	BUG_ON(err == NOTIFY_BAD);
+	cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_ONLINE, bcpu);
+	register_cpu_notifier(&cpu_stop_cpu_notifier);
 
-	/* Wait for kthread_stop */
-	set_current_state(TASK_INTERRUPTIBLE);
-	while (!kthread_should_stop()) {
-		schedule();
-		set_current_state(TASK_INTERRUPTIBLE);
-	}
-	__set_current_state(TASK_RUNNING);
-	return ret;
+	return 0;
 }
+early_initcall(cpu_stop_init);
 
-struct task_struct *__stop_machine_run(int (*fn)(void *), void *data,
-				       unsigned int cpu)
+#ifdef CONFIG_STOP_MACHINE
+
+/* This controls the threads on each CPU. */
+enum stopmachine_state {
+	/* Dummy starting state for thread. */
+	STOPMACHINE_NONE,
+	/* Awaiting everyone to be scheduled. */
+	STOPMACHINE_PREPARE,
+	/* Disable interrupts. */
+	STOPMACHINE_DISABLE_IRQ,
+	/* Run the function */
+	STOPMACHINE_RUN,
+	/* Exit */
+	STOPMACHINE_EXIT,
+};
+
+struct stop_machine_data {
+	int			(*fn)(void *);
+	void			*data;
+	/* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */
+	unsigned int		num_threads;
+	const struct cpumask	*active_cpus;
+
+	enum stopmachine_state	state;
+	atomic_t		thread_ack;
+};
+
+static void set_state(struct stop_machine_data *smdata,
+		      enum stopmachine_state newstate)
 {
-	static DEFINE_MUTEX(stopmachine_mutex);
-	struct stop_machine_data smdata;
-	struct task_struct *p;
+	/* Reset ack counter. */
+	atomic_set(&smdata->thread_ack, smdata->num_threads);
+	smp_wmb();
+	smdata->state = newstate;
+}
+
+/* Last one to ack a state moves to the next state. */
+static void ack_state(struct stop_machine_data *smdata)
+{
+	if (atomic_dec_and_test(&smdata->thread_ack))
+		set_state(smdata, smdata->state + 1);
+}
+
+/* This is the cpu_stop function which stops the CPU. */
+static int stop_machine_cpu_stop(void *data)
+{
+	struct stop_machine_data *smdata = data;
+	enum stopmachine_state curstate = STOPMACHINE_NONE;
+	int cpu = smp_processor_id(), err = 0;
+	bool is_active;
 
-	smdata.fn = fn;
-	smdata.data = data;
-	init_completion(&smdata.done);
+	if (!smdata->active_cpus)
+		is_active = cpu == cpumask_first(cpu_online_mask);
+	else
+		is_active = cpumask_test_cpu(cpu, smdata->active_cpus);
 
-	mutex_lock(&stopmachine_mutex);
+	/* Simple state machine */
+	do {
+		/* Chill out and ensure we re-read stopmachine_state. */
+		cpu_relax();
+		if (smdata->state != curstate) {
+			curstate = smdata->state;
+			switch (curstate) {
+			case STOPMACHINE_DISABLE_IRQ:
+				local_irq_disable();
+				hard_irq_disable();
+				break;
+			case STOPMACHINE_RUN:
+				if (is_active)
+					err = smdata->fn(smdata->data);
+				break;
+			default:
+				break;
+			}
+			ack_state(smdata);
+		}
+	} while (curstate != STOPMACHINE_EXIT);
 
-	/* If they don't care which CPU fn runs on, bind to any online one. */
-	if (cpu == NR_CPUS)
-		cpu = raw_smp_processor_id();
+	local_irq_enable();
+	return err;
+}
 
-	p = kthread_create(do_stop, &smdata, "kstopmachine");
-	if (!IS_ERR(p)) {
-		struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
+int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus)
+{
+	struct stop_machine_data smdata = { .fn = fn, .data = data,
+					    .num_threads = num_online_cpus(),
+					    .active_cpus = cpus };
 
-		/* One high-prio thread per cpu.  We'll do this one. */
-		sched_setscheduler(p, SCHED_FIFO, &param);
-		kthread_bind(p, cpu);
-		wake_up_process(p);
-		wait_for_completion(&smdata.done);
-	}
-	mutex_unlock(&stopmachine_mutex);
-	return p;
+	/* Set the initial state and stop all online cpus. */
+	set_state(&smdata, STOPMACHINE_PREPARE);
+	return stop_cpus(cpu_online_mask, stop_machine_cpu_stop, &smdata);
 }
 
-int stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
+int stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus)
 {
-	struct task_struct *p;
 	int ret;
 
 	/* No CPUs can come up or down during this. */
 	get_online_cpus();
-	p = __stop_machine_run(fn, data, cpu);
-	if (!IS_ERR(p))
-		ret = kthread_stop(p);
-	else
-		ret = PTR_ERR(p);
+	ret = __stop_machine(fn, data, cpus);
 	put_online_cpus();
-
 	return ret;
 }
-EXPORT_SYMBOL_GPL(stop_machine_run);
+EXPORT_SYMBOL_GPL(stop_machine);
+
+#endif	/* CONFIG_STOP_MACHINE */