Simplify stop_machine (ffdb5976) · Commits · 戴 / test

include/linux/stop_machine.h

+8 −12

Original line number	Diff line number	Diff line
		@@ -17,13 +17,12 @@
		* @data: the data ptr for the @fn()
		* @cpu: if @cpu == n, run @fn() on cpu n
		* if @cpu == NR_CPUS, run @fn() on any cpu
		* if @cpu == ALL_CPUS, run @fn() first on the calling cpu, and then
		* concurrently on all the other cpus
		* if @cpu == ALL_CPUS, run @fn() on every online CPU.
		*
		* Description: This causes a thread to be scheduled on every other cpu,
		* each of which disables interrupts, and finally interrupts are disabled
		* on the current CPU. The result is that noone is holding a spinlock
		* or inside any other preempt-disabled region when @fn() runs.
		* Description: This causes a thread to be scheduled on every cpu,
		* each of which disables interrupts. The result is that noone is
		* holding a spinlock or inside any other preempt-disabled region when
		* @fn() runs.
		*
		* This can be thought of as a very heavy write lock, equivalent to
		* grabbing every spinlock in the kernel. */
		@@ -35,13 +34,10 @@ int stop_machine_run(int (fn)(void ), void *data, unsigned int cpu);
		* @data: the data ptr for the @fn
		* @cpu: the cpu to run @fn on (or any, if @cpu == NR_CPUS.
		*
		* Description: This is a special version of the above, which returns the
		* thread which has run @fn(): kthread_stop will return the return value
		* of @fn(). Used by hotplug cpu.
		* Description: This is a special version of the above, which assumes cpus
		* won't come or go while it's being called. Used by hotplug cpu.
		*/
		struct task_struct __stop_machine_run(int (fn)(void ), void data,
		unsigned int cpu);

		int __stop_machine_run(int (fn)(void ), void *data, unsigned int cpu);
		#else

		static inline int stop_machine_run(int (fn)(void ), void *data,

kernel/cpu.c

+3 −10

Original line number	Diff line number	Diff line
		@@ -216,7 +216,6 @@ static int __ref take_cpu_down(void *_param)
		static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
		{
		int err, nr_calls = 0;
		struct task_struct *p;
		cpumask_t old_allowed, tmp;
		void hcpu = (void )(long)cpu;
		unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
		@@ -250,20 +249,16 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
		cpu_clear(cpu, tmp);
		set_cpus_allowed_ptr(current, &tmp);

		p = __stop_machine_run(take_cpu_down, &tcd_param, cpu);
		err = __stop_machine_run(take_cpu_down, &tcd_param, cpu);

		if (IS_ERR(p) \|\| cpu_online(cpu)) {
		if (err \|\| cpu_online(cpu)) {
		/* CPU didn't die: tell everyone. Can't complain. */
		if (raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED \| mod,
		hcpu) == NOTIFY_BAD)
		BUG();

		if (IS_ERR(p)) {
		err = PTR_ERR(p);
		goto out_allowed;
		}
		goto out_thread;
		}

		/* Wait for it to sleep (leaving idle task). */
		while (!idle_cpu(cpu))
		@@ -279,8 +274,6 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)

		check_for_tasks(cpu);

		out_thread:
		err = kthread_stop(p);
		out_allowed:
		set_cpus_allowed_ptr(current, &old_allowed);
		out_release:

kernel/stop_machine.c

+125 −168

Original line number	Diff line number	Diff line
		/* Copyright 2005 Rusty Russell rusty@rustcorp.com.au IBM Corporation.
		/* Copyright 2008, 2005 Rusty Russell rusty@rustcorp.com.au IBM Corporation.
		* GPL v2 and any later version.
		*/
		#include <linux/cpu.h>
		@@ -13,220 +13,177 @@
		#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. */

		/* Thread to stop each CPU in user context. */
		/* This controls the threads on each CPU. */
		enum stopmachine_state {
		STOPMACHINE_WAIT,
		/* 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,
		};
		static enum stopmachine_state state;

		struct stop_machine_data {
		int (fn)(void );
		void *data;
		struct completion done;
		int run_all;
		} smdata;

		static enum stopmachine_state stopmachine_state;
		static unsigned int stopmachine_num_threads;
		static atomic_t stopmachine_thread_ack;

		static int stopmachine(void *cpu)
		{
		int irqs_disabled = 0;
		int prepared = 0;
		int ran = 0;
		cpumask_of_cpu_ptr(cpumask, (int)(long)cpu);

		set_cpus_allowed_ptr(current, cpumask);

		/* Ack: we are alive */
		smp_mb(); /* Theoretically the ack = 0 might not be on this CPU yet. */
		atomic_inc(&stopmachine_thread_ack);

		/* 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);
		} else if (stopmachine_state == STOPMACHINE_RUN && !ran) {
		smdata.fn(smdata.data);
		ran = 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();
		}

		/* Ack: we are exiting. */
		smp_mb(); /* Must read state first. */
		atomic_inc(&stopmachine_thread_ack);
		int fnret;
		};

		if (irqs_disabled)
		local_irq_enable();
		if (prepared)
		preempt_enable();
		/* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */
		static unsigned int num_threads;
		static atomic_t thread_ack;
		static struct completion finished;
		static DEFINE_MUTEX(lock);

		return 0;
		}

		/* Change the thread state */
		static void stopmachine_set_state(enum stopmachine_state state)
		static void set_state(enum stopmachine_state newstate)
		{
		atomic_set(&stopmachine_thread_ack, 0);
		/* Reset ack counter. */
		atomic_set(&thread_ack, num_threads);
		smp_wmb();
		stopmachine_state = state;
		while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
		cpu_relax();
		state = newstate;
		}

		static int stop_machine(void)
		/* Last one to ack a state moves to the next state. */
		static void ack_state(void)
		{
		int i, ret = 0;

		atomic_set(&stopmachine_thread_ack, 0);
		stopmachine_num_threads = 0;
		stopmachine_state = STOPMACHINE_WAIT;

		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++;
		}

		/* Wait for them all to come to life. */
		while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads) {
		yield();
		cpu_relax();
		if (atomic_dec_and_test(&thread_ack)) {
		/* If we're the last one to ack the EXIT, we're finished. */
		if (state == STOPMACHINE_EXIT)
		complete(&finished);
		else
		set_state(state + 1);
		}

		/* If some failed, kill them all. */
		if (ret < 0) {
		stopmachine_set_state(STOPMACHINE_EXIT);
		return ret;
		}

		/* Now they are all started, make them hold the CPUs, ready. */
		preempt_disable();
		stopmachine_set_state(STOPMACHINE_PREPARE);
		/* This is the actual thread which stops the CPU. It exits by itself rather
		* than waiting for kthread_stop(), because it's easier for hotplug CPU. */
		static int stop_cpu(struct stop_machine_data *smdata)
		{
		enum stopmachine_state curstate = STOPMACHINE_NONE;
		int uninitialized_var(ret);

		/* Make them disable irqs. */
		/* Simple state machine */
		do {
		/* Chill out and ensure we re-read stopmachine_state. */
		cpu_relax();
		if (state != curstate) {
		curstate = state;
		switch (curstate) {
		case STOPMACHINE_DISABLE_IRQ:
		local_irq_disable();
		hard_irq_disable();
		stopmachine_set_state(STOPMACHINE_DISABLE_IRQ);

		return 0;
		break;
		case STOPMACHINE_RUN:
		/* \|= allows error detection if functions on
		* multiple CPUs. */
		smdata->fnret \|= smdata->fn(smdata->data);
		break;
		default:
		break;
		}
		ack_state();
		}
		} while (curstate != STOPMACHINE_EXIT);

		static void restart_machine(void)
		{
		stopmachine_set_state(STOPMACHINE_EXIT);
		local_irq_enable();
		preempt_enable_no_resched();
		do_exit(0);
		}

		static void run_other_cpus(void)
		/* Callback for CPUs which aren't supposed to do anything. */
		static int chill(void *unused)
		{
		stopmachine_set_state(STOPMACHINE_RUN);
		return 0;
		}

		static int do_stop(void *_smdata)
		int __stop_machine_run(int (fn)(void ), void *data, unsigned int cpu)
		{
		struct stop_machine_data *smdata = _smdata;
		int ret;
		int i, err;
		struct stop_machine_data active, idle;
		struct task_struct **threads;

		active.fn = fn;
		active.data = data;
		active.fnret = 0;
		idle.fn = chill;
		idle.data = NULL;

		/* If they don't care which cpu fn runs on, just pick one. */
		if (cpu == NR_CPUS)
		cpu = any_online_cpu(cpu_online_map);

		/* This could be too big for stack on large machines. */
		threads = kcalloc(NR_CPUS, sizeof(threads[0]), GFP_KERNEL);
		if (!threads)
		return -ENOMEM;

		/* Set up initial state. */
		mutex_lock(&lock);
		init_completion(&finished);
		num_threads = num_online_cpus();
		set_state(STOPMACHINE_PREPARE);

		ret = stop_machine();
		if (ret == 0) {
		ret = smdata->fn(smdata->data);
		if (smdata->run_all)
		run_other_cpus();
		restart_machine();
		}
		for_each_online_cpu(i) {
		struct stop_machine_data *smdata;
		struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };

		/* We're done: you can kthread_stop us now */
		complete(&smdata->done);
		if (cpu == ALL_CPUS \|\| i == cpu)
		smdata = &active;
		else
		smdata = &idle;

		/* 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;
		threads[i] = kthread_create((void *)stop_cpu, smdata, "kstop%u",
		i);
		if (IS_ERR(threads[i])) {
		err = PTR_ERR(threads[i]);
		threads[i] = NULL;
		goto kill_threads;
		}

		struct task_struct __stop_machine_run(int (fn)(void ), void data,
		unsigned int cpu)
		{
		static DEFINE_MUTEX(stopmachine_mutex);
		struct stop_machine_data smdata;
		struct task_struct *p;
		/* Place it onto correct cpu. */
		kthread_bind(threads[i], i);

		mutex_lock(&stopmachine_mutex);
		/* Make it highest prio. */
		if (sched_setscheduler_nocheck(threads[i], SCHED_FIFO, &param))
		BUG();
		}

		smdata.fn = fn;
		smdata.data = data;
		smdata.run_all = (cpu == ALL_CPUS) ? 1 : 0;
		init_completion(&smdata.done);
		/* We've created all the threads. Wake them all: hold this CPU so one
		* doesn't hit this CPU until we're ready. */
		cpu = get_cpu();
		for_each_online_cpu(i)
		wake_up_process(threads[i]);

		smp_wmb(); /* make sure other cpus see smdata updates */
		/* This will release the thread on our CPU. */
		put_cpu();
		wait_for_completion(&finished);
		mutex_unlock(&lock);

		/* If they don't care which CPU fn runs on, bind to any online one. */
		if (cpu == NR_CPUS \|\| cpu == ALL_CPUS)
		cpu = raw_smp_processor_id();
		kfree(threads);

		p = kthread_create(do_stop, &smdata, "kstopmachine");
		if (!IS_ERR(p)) {
		struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
		return active.fnret;

		/* One high-prio thread per cpu. We'll do this one. */
		sched_setscheduler_nocheck(p, SCHED_FIFO, &param);
		kthread_bind(p, cpu);
		wake_up_process(p);
		wait_for_completion(&smdata.done);
		}
		mutex_unlock(&stopmachine_mutex);
		return p;
		kill_threads:
		for_each_online_cpu(i)
		if (threads[i])
		kthread_stop(threads[i]);
		mutex_unlock(&lock);

		kfree(threads);
		return err;
		}

		int stop_machine_run(int (fn)(void ), void *data, unsigned int cpu)
		{
		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_run(fn, data, cpu);
		put_online_cpus();

		return ret;

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