cpu.c

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/* CPU control.
 * (C) 2001, 2002, 2003, 2004 Rusty Russell
 *
 * This code is licenced under the GPL.
 */
#include <linux/proc_fs.h>
#include <linux/smp.h>
#include <linux/init.h>
#include <linux/notifier.h>
#include <linux/sched.h>
#include <linux/unistd.h>
#include <linux/cpu.h>
#include <linux/oom.h>
#include <linux/rcupdate.h>
#include <linux/export.h>
#include <linux/bug.h>
#include <linux/kthread.h>
#include <linux/stop_machine.h>
#include <linux/mutex.h>
#include <linux/gfp.h>
#include <linux/suspend.h>

#include "smpboot.h"

#ifdef CONFIG_SMP
/* Serializes the updates to cpu_online_mask, cpu_present_mask */
static DEFINE_MUTEX(cpu_add_remove_lock);

/*
 * The following two API's must be used when attempting
 * to serialize the updates to cpu_online_mask, cpu_present_mask.
 */
void cpu_maps_update_begin(void)
{
    mutex_lock(&cpu_add_remove_lock);
}

void cpu_maps_update_done(void)
{
    mutex_unlock(&cpu_add_remove_lock);
}

static RAW_NOTIFIER_HEAD(cpu_chain);

/* If set, cpu_up and cpu_down will return -EBUSY and do nothing.
 * Should always be manipulated under cpu_add_remove_lock
 */
static int cpu_hotplug_disabled;

#ifdef CONFIG_HOTPLUG_CPU

static struct {
    struct task_struct *active_writer;
    struct mutex lock; /* Synchronizes accesses to refcount, */
    /*
     * Also blocks the new readers during
     * an ongoing cpu hotplug operation.
     */
    int refcount;
} cpu_hotplug = {
    .active_writer = NULL,
    .lock = __MUTEX_INITIALIZER(cpu_hotplug.lock),
    .refcount = 0,
};

void get_online_cpus(void)
{
    might_sleep();
    if (cpu_hotplug.active_writer == current)
        return;
    mutex_lock(&cpu_hotplug.lock);
    cpu_hotplug.refcount++;
    mutex_unlock(&cpu_hotplug.lock);

}
EXPORT_SYMBOL_GPL(get_online_cpus);

void put_online_cpus(void)
{
    if (cpu_hotplug.active_writer == current)
        return;
    mutex_lock(&cpu_hotplug.lock);

    if (WARN_ON(!cpu_hotplug.refcount))
        cpu_hotplug.refcount++; /* try to fix things up */

    if (!--cpu_hotplug.refcount && unlikely(cpu_hotplug.active_writer))
        wake_up_process(cpu_hotplug.active_writer);
    mutex_unlock(&cpu_hotplug.lock);

}
EXPORT_SYMBOL_GPL(put_online_cpus);

/*
 * This ensures that the hotplug operation can begin only when the
 * refcount goes to zero.
 *
 * Note that during a cpu-hotplug operation, the new readers, if any,
 * will be blocked by the cpu_hotplug.lock
 *
 * Since cpu_hotplug_begin() is always called after invoking
 * cpu_maps_update_begin(), we can be sure that only one writer is active.
 *
 * Note that theoretically, there is a possibility of a livelock:
 * - Refcount goes to zero, last reader wakes up the sleeping
 *   writer.
 * - Last reader unlocks the cpu_hotplug.lock.
 * - A new reader arrives at this moment, bumps up the refcount.
 * - The writer acquires the cpu_hotplug.lock finds the refcount
 *   non zero and goes to sleep again.
 *
 * However, this is very difficult to achieve in practice since
 * get_online_cpus() not an api which is called all that often.
 *
 */
static void cpu_hotplug_begin(void)
{
    cpu_hotplug.active_writer = current;

    for (;;) {
        mutex_lock(&cpu_hotplug.lock);
        if (likely(!cpu_hotplug.refcount))
            break;
        __set_current_state(TASK_UNINTERRUPTIBLE);
        mutex_unlock(&cpu_hotplug.lock);
        schedule();
    }
}

static void cpu_hotplug_done(void)
{
    cpu_hotplug.active_writer = NULL;
    mutex_unlock(&cpu_hotplug.lock);
}

#else /* #if CONFIG_HOTPLUG_CPU */
static void cpu_hotplug_begin(void) {}
static void cpu_hotplug_done(void) {}
#endif  /* #else #if CONFIG_HOTPLUG_CPU */

/* Need to know about CPUs going up/down? */
int __ref register_cpu_notifier(struct notifier_block *nb)
{
    int ret;
    cpu_maps_update_begin();
    ret = raw_notifier_chain_register(&cpu_chain, nb);
    cpu_maps_update_done();
    return ret;
}

static int __cpu_notify(unsigned long val, void *v, int nr_to_call,
            int *nr_calls)
{
    int ret;

    ret = __raw_notifier_call_chain(&cpu_chain, val, v, nr_to_call,
                    nr_calls);

    return notifier_to_errno(ret);
}

static int cpu_notify(unsigned long val, void *v)
{
    return __cpu_notify(val, v, -1, NULL);
}

#ifdef CONFIG_HOTPLUG_CPU

static void cpu_notify_nofail(unsigned long val, void *v)
{
    BUG_ON(cpu_notify(val, v));
}
EXPORT_SYMBOL(register_cpu_notifier);

void __ref unregister_cpu_notifier(struct notifier_block *nb)
{
    cpu_maps_update_begin();
    raw_notifier_chain_unregister(&cpu_chain, nb);
    cpu_maps_update_done();
}
EXPORT_SYMBOL(unregister_cpu_notifier);

void clear_tasks_mm_cpumask(int cpu)
{
    struct task_struct *p;

    /*
     * This function is called after the cpu is taken down and marked
     * offline, so its not like new tasks will ever get this cpu set in
     * their mm mask. -- Peter Zijlstra
     * Thus, we may use rcu_read_lock() here, instead of grabbing
     * full-fledged tasklist_lock.
     */
    WARN_ON(cpu_online(cpu));
    rcu_read_lock();
    for_each_process(p) {
        struct task_struct *t;

        /*
         * Main thread might exit, but other threads may still have
         * a valid mm. Find one.
         */
        t = find_lock_task_mm(p);
        if (!t)
            continue;
        cpumask_clear_cpu(cpu, mm_cpumask(t->mm));
        task_unlock(t);
    }
    rcu_read_unlock();
}

static inline void check_for_tasks(int cpu)
{
    struct task_struct *p;

    write_lock_irq(&tasklist_lock);
    for_each_process(p) {
        if (task_cpu(p) == cpu && p->state == TASK_RUNNING &&
            (p->utime || p->stime))
            printk(KERN_WARNING "Task %s (pid = %d) is on cpu %d "
                "(state = %ld, flags = %x)\n",
                p->comm, task_pid_nr(p), cpu,
                p->state, p->flags);
    }
    write_unlock_irq(&tasklist_lock);
}

struct take_cpu_down_param {
    unsigned long mod;
    void *hcpu;
};

/* Take this CPU down. */
static int __ref take_cpu_down(void *_param)
{
    struct take_cpu_down_param *param = _param;
    int err;

    /* Ensure this CPU doesn't handle any more interrupts. */
    err = __cpu_disable();
    if (err < 0)
        return err;

    cpu_notify(CPU_DYING | param->mod, param->hcpu);
    return 0;
}

/* Requires cpu_add_remove_lock to be held */
static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
{
    int err, nr_calls = 0;
    void *hcpu = (void *)(long)cpu;
    unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
    struct take_cpu_down_param tcd_param = {
        .mod = mod,
        .hcpu = hcpu,
    };

    if (num_online_cpus() == 1)
        return -EBUSY;

    if (!cpu_online(cpu))
        return -EINVAL;

    cpu_hotplug_begin();

    err = __cpu_notify(CPU_DOWN_PREPARE | mod, hcpu, -1, &nr_calls);
    if (err) {
        nr_calls--;
        __cpu_notify(CPU_DOWN_FAILED | mod, hcpu, nr_calls, NULL);
        printk("%s: attempt to take down CPU %u failed\n",
                __func__, cpu);
        goto out_release;
    }
    smpboot_park_threads(cpu);

    err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
    if (err) {
        /* CPU didn't die: tell everyone.  Can't complain. */
        smpboot_unpark_threads(cpu);
        cpu_notify_nofail(CPU_DOWN_FAILED | mod, hcpu);
        goto out_release;
    }
    BUG_ON(cpu_online(cpu));

    /*
     * The migration_call() CPU_DYING callback will have removed all
     * runnable tasks from the cpu, there's only the idle task left now
     * that the migration thread is done doing the stop_machine thing.
     *
     * Wait for the stop thread to go away.
     */
    while (!idle_cpu(cpu))
        cpu_relax();

    /* This actually kills the CPU. */
    __cpu_die(cpu);

    /* CPU is completely dead: tell everyone.  Too late to complain. */
    cpu_notify_nofail(CPU_DEAD | mod, hcpu);

    check_for_tasks(cpu);

out_release:
    cpu_hotplug_done();
    if (!err)
        cpu_notify_nofail(CPU_POST_DEAD | mod, hcpu);
    return err;
}

int __ref cpu_down(unsigned int cpu)
{
    int err;

    cpu_maps_update_begin();

    if (cpu_hotplug_disabled) {
        err = -EBUSY;
        goto out;
    }

    err = _cpu_down(cpu, 0);

out:
    cpu_maps_update_done();
    return err;
}
EXPORT_SYMBOL(cpu_down);
#endif /*CONFIG_HOTPLUG_CPU*/

/* Requires cpu_add_remove_lock to be held */
static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
{
    int ret, nr_calls = 0;
    void *hcpu = (void *)(long)cpu;
    unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
    struct task_struct *idle;

    if (cpu_online(cpu) || !cpu_present(cpu))
        return -EINVAL;

    cpu_hotplug_begin();

    idle = idle_thread_get(cpu);
    if (IS_ERR(idle)) {
        ret = PTR_ERR(idle);
        goto out;
    }

    ret = smpboot_create_threads(cpu);
    if (ret)
        goto out;

    ret = __cpu_notify(CPU_UP_PREPARE | mod, hcpu, -1, &nr_calls);
    if (ret) {
        nr_calls--;
        printk(KERN_WARNING "%s: attempt to bring up CPU %u failed\n",
                __func__, cpu);
        goto out_notify;
    }

    /* Arch-specific enabling code. */
    ret = __cpu_up(cpu, idle);
    if (ret != 0)
        goto out_notify;
    BUG_ON(!cpu_online(cpu));

    /* Wake the per cpu threads */
    smpboot_unpark_threads(cpu);

    /* Now call notifier in preparation. */
    cpu_notify(CPU_ONLINE | mod, hcpu);

out_notify:
    if (ret != 0)
        __cpu_notify(CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL);
out:
    cpu_hotplug_done();

    return ret;
}

int __cpuinit cpu_up(unsigned int cpu)
{
    int err = 0;

#ifdef  CONFIG_MEMORY_HOTPLUG
    int nid;
    pg_data_t   *pgdat;
#endif

    if (!cpu_possible(cpu)) {
        printk(KERN_ERR "can't online cpu %d because it is not "
            "configured as may-hotadd at boot time\n", cpu);
#if defined(CONFIG_IA64)
        printk(KERN_ERR "please check additional_cpus= boot "
                "parameter\n");
#endif
        return -EINVAL;
    }

#ifdef  CONFIG_MEMORY_HOTPLUG
    nid = cpu_to_node(cpu);
    if (!node_online(nid)) {
        err = mem_online_node(nid);
        if (err)
            return err;
    }

    pgdat = NODE_DATA(nid);
    if (!pgdat) {
        printk(KERN_ERR
            "Can't online cpu %d due to NULL pgdat\n", cpu);
        return -ENOMEM;
    }

    if (pgdat->node_zonelists->_zonerefs->zone == NULL) {
        mutex_lock(&zonelists_mutex);
        build_all_zonelists(NULL, NULL);
        mutex_unlock(&zonelists_mutex);
    }
#endif

    cpu_maps_update_begin();

    if (cpu_hotplug_disabled) {
        err = -EBUSY;
        goto out;
    }

    err = _cpu_up(cpu, 0);

out:
    cpu_maps_update_done();
    return err;
}
EXPORT_SYMBOL_GPL(cpu_up);

#ifdef CONFIG_PM_SLEEP_SMP
static cpumask_var_t frozen_cpus;

int disable_nonboot_cpus(void)
{
    int cpu, first_cpu, error = 0;

    cpu_maps_update_begin();
    first_cpu = cpumask_first(cpu_online_mask);
    /*
     * We take down all of the non-boot CPUs in one shot to avoid races
     * with the userspace trying to use the CPU hotplug at the same time
     */
    cpumask_clear(frozen_cpus);

    printk("Disabling non-boot CPUs ...\n");
    for_each_online_cpu(cpu) {
        if (cpu == first_cpu)
            continue;
        error = _cpu_down(cpu, 1);
        if (!error)
            cpumask_set_cpu(cpu, frozen_cpus);
        else {
            printk(KERN_ERR "Error taking CPU%d down: %d\n",
                cpu, error);
            break;
        }
    }

    if (!error) {
        BUG_ON(num_online_cpus() > 1);
        /* Make sure the CPUs won't be enabled by someone else */
        cpu_hotplug_disabled = 1;
    } else {
        printk(KERN_ERR "Non-boot CPUs are not disabled\n");
    }
    cpu_maps_update_done();
    return error;
}

void __weak arch_enable_nonboot_cpus_begin(void)
{
}

void __weak arch_enable_nonboot_cpus_end(void)
{
}

void __ref enable_nonboot_cpus(void)
{
    int cpu, error;

    /* Allow everyone to use the CPU hotplug again */
    cpu_maps_update_begin();
    cpu_hotplug_disabled = 0;
    if (cpumask_empty(frozen_cpus))
        goto out;

    printk(KERN_INFO "Enabling non-boot CPUs ...\n");

    arch_enable_nonboot_cpus_begin();

    for_each_cpu(cpu, frozen_cpus) {
        error = _cpu_up(cpu, 1);
        if (!error) {
            printk(KERN_INFO "CPU%d is up\n", cpu);
            continue;
        }
        printk(KERN_WARNING "Error taking CPU%d up: %d\n", cpu, error);
    }

    arch_enable_nonboot_cpus_end();

    cpumask_clear(frozen_cpus);
out:
    cpu_maps_update_done();
}

static int __init alloc_frozen_cpus(void)
{
    if (!alloc_cpumask_var(&frozen_cpus, GFP_KERNEL|__GFP_ZERO))
        return -ENOMEM;
    return 0;
}
core_initcall(alloc_frozen_cpus);

/*
 * Prevent regular CPU hotplug from racing with the freezer, by disabling CPU
 * hotplug when tasks are about to be frozen. Also, don't allow the freezer
 * to continue until any currently running CPU hotplug operation gets
 * completed.
 * To modify the 'cpu_hotplug_disabled' flag, we need to acquire the
 * 'cpu_add_remove_lock'. And this same lock is also taken by the regular
 * CPU hotplug path and released only after it is complete. Thus, we
 * (and hence the freezer) will block here until any currently running CPU
 * hotplug operation gets completed.
 */
void cpu_hotplug_disable_before_freeze(void)
{
    cpu_maps_update_begin();
    cpu_hotplug_disabled = 1;
    cpu_maps_update_done();
}


/*
 * When tasks have been thawed, re-enable regular CPU hotplug (which had been
 * disabled while beginning to freeze tasks).
 */
void cpu_hotplug_enable_after_thaw(void)
{
    cpu_maps_update_begin();
    cpu_hotplug_disabled = 0;
    cpu_maps_update_done();
}

/*
 * When callbacks for CPU hotplug notifications are being executed, we must
 * ensure that the state of the system with respect to the tasks being frozen
 * or not, as reported by the notification, remains unchanged *throughout the
 * duration* of the execution of the callbacks.
 * Hence we need to prevent the freezer from racing with regular CPU hotplug.
 *
 * This synchronization is implemented by mutually excluding regular CPU
 * hotplug and Suspend/Hibernate call paths by hooking onto the Suspend/
 * Hibernate notifications.
 */
static int
cpu_hotplug_pm_callback(struct notifier_block *nb,
            unsigned long action, void *ptr)
{
    switch (action) {

    case PM_SUSPEND_PREPARE:
    case PM_HIBERNATION_PREPARE:
        cpu_hotplug_disable_before_freeze();
        break;

    case PM_POST_SUSPEND:
    case PM_POST_HIBERNATION:
        cpu_hotplug_enable_after_thaw();
        break;

    default:
        return NOTIFY_DONE;
    }

    return NOTIFY_OK;
}


static int __init cpu_hotplug_pm_sync_init(void)
{
    pm_notifier(cpu_hotplug_pm_callback, 0);
    return 0;
}
core_initcall(cpu_hotplug_pm_sync_init);

#endif /* CONFIG_PM_SLEEP_SMP */

void __cpuinit notify_cpu_starting(unsigned int cpu)
{
    unsigned long val = CPU_STARTING;

#ifdef CONFIG_PM_SLEEP_SMP
    if (frozen_cpus != NULL && cpumask_test_cpu(cpu, frozen_cpus))
        val = CPU_STARTING_FROZEN;
#endif /* CONFIG_PM_SLEEP_SMP */
    cpu_notify(val, (void *)(long)cpu);
}

#endif /* CONFIG_SMP */

/*
 * cpu_bit_bitmap[] is a special, "compressed" data structure that
 * represents all NR_CPUS bits binary values of 1<<nr.
 *
 * It is used by cpumask_of() to get a constant address to a CPU
 * mask value that has a single bit set only.
 */

/* cpu_bit_bitmap[0] is empty - so we can back into it */
#define MASK_DECLARE_1(x)   [x+1][0] = (1UL << (x))
#define MASK_DECLARE_2(x)   MASK_DECLARE_1(x), MASK_DECLARE_1(x+1)
#define MASK_DECLARE_4(x)   MASK_DECLARE_2(x), MASK_DECLARE_2(x+2)
#define MASK_DECLARE_8(x)   MASK_DECLARE_4(x), MASK_DECLARE_4(x+4)

const unsigned long cpu_bit_bitmap[BITS_PER_LONG+1][BITS_TO_LONGS(NR_CPUS)] = {

    MASK_DECLARE_8(0),  MASK_DECLARE_8(8),
    MASK_DECLARE_8(16), MASK_DECLARE_8(24),
#if BITS_PER_LONG > 32
    MASK_DECLARE_8(32), MASK_DECLARE_8(40),
    MASK_DECLARE_8(48), MASK_DECLARE_8(56),
#endif
};
EXPORT_SYMBOL_GPL(cpu_bit_bitmap);

const DECLARE_BITMAP(cpu_all_bits, NR_CPUS) = CPU_BITS_ALL;
EXPORT_SYMBOL(cpu_all_bits);

#ifdef CONFIG_INIT_ALL_POSSIBLE
static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly
    = CPU_BITS_ALL;
#else
static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly;
#endif
const struct cpumask *const cpu_possible_mask = to_cpumask(cpu_possible_bits);
EXPORT_SYMBOL(cpu_possible_mask);

static DECLARE_BITMAP(cpu_online_bits, CONFIG_NR_CPUS) __read_mostly;
const struct cpumask *const cpu_online_mask = to_cpumask(cpu_online_bits);
EXPORT_SYMBOL(cpu_online_mask);

static DECLARE_BITMAP(cpu_present_bits, CONFIG_NR_CPUS) __read_mostly;
const struct cpumask *const cpu_present_mask = to_cpumask(cpu_present_bits);
EXPORT_SYMBOL(cpu_present_mask);

static DECLARE_BITMAP(cpu_active_bits, CONFIG_NR_CPUS) __read_mostly;
const struct cpumask *const cpu_active_mask = to_cpumask(cpu_active_bits);
EXPORT_SYMBOL(cpu_active_mask);

void set_cpu_possible(unsigned int cpu, bool possible)
{
    if (possible)
        cpumask_set_cpu(cpu, to_cpumask(cpu_possible_bits));
    else
        cpumask_clear_cpu(cpu, to_cpumask(cpu_possible_bits));
}

void set_cpu_present(unsigned int cpu, bool present)
{
    if (present)
        cpumask_set_cpu(cpu, to_cpumask(cpu_present_bits));
    else
        cpumask_clear_cpu(cpu, to_cpumask(cpu_present_bits));
}

void set_cpu_online(unsigned int cpu, bool online)
{
    if (online)
        cpumask_set_cpu(cpu, to_cpumask(cpu_online_bits));
    else
        cpumask_clear_cpu(cpu, to_cpumask(cpu_online_bits));
}

void set_cpu_active(unsigned int cpu, bool active)
{
    if (active)
        cpumask_set_cpu(cpu, to_cpumask(cpu_active_bits));
    else
        cpumask_clear_cpu(cpu, to_cpumask(cpu_active_bits));
}

void init_cpu_present(const struct cpumask *src)
{
    cpumask_copy(to_cpumask(cpu_present_bits), src);
}

void init_cpu_possible(const struct cpumask *src)
{
    cpumask_copy(to_cpumask(cpu_possible_bits), src);
}

void init_cpu_online(const struct cpumask *src)
{
    cpumask_copy(to_cpumask(cpu_online_bits), src);
}