padata.c

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/*
 * padata.c - generic interface to process data streams in parallel
 *
 * See Documentation/padata.txt for an api documentation.
 *
 * Copyright (C) 2008, 2009 secunet Security Networks AG
 * Copyright (C) 2008, 2009 Steffen Klassert <[email protected]>
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms and conditions of the GNU General Public License,
 * version 2, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA.
 */

#include <linux/export.h>
#include <linux/cpumask.h>
#include <linux/err.h>
#include <linux/cpu.h>
#include <linux/padata.h>
#include <linux/mutex.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/sysfs.h>
#include <linux/rcupdate.h>

#define MAX_OBJ_NUM 1000

static int padata_index_to_cpu(struct parallel_data *pd, int cpu_index)
{
    int cpu, target_cpu;

    target_cpu = cpumask_first(pd->cpumask.pcpu);
    for (cpu = 0; cpu < cpu_index; cpu++)
        target_cpu = cpumask_next(target_cpu, pd->cpumask.pcpu);

    return target_cpu;
}

static int padata_cpu_hash(struct parallel_data *pd)
{
    int cpu_index;

    /*
     * Hash the sequence numbers to the cpus by taking
     * seq_nr mod. number of cpus in use.
     */

    spin_lock(&pd->seq_lock);
    cpu_index =  pd->seq_nr % cpumask_weight(pd->cpumask.pcpu);
    pd->seq_nr++;
    spin_unlock(&pd->seq_lock);

    return padata_index_to_cpu(pd, cpu_index);
}

static void padata_parallel_worker(struct work_struct *parallel_work)
{
    struct padata_parallel_queue *pqueue;
    struct parallel_data *pd;
    struct padata_instance *pinst;
    LIST_HEAD(local_list);

    local_bh_disable();
    pqueue = container_of(parallel_work,
                  struct padata_parallel_queue, work);
    pd = pqueue->pd;
    pinst = pd->pinst;

    spin_lock(&pqueue->parallel.lock);
    list_replace_init(&pqueue->parallel.list, &local_list);
    spin_unlock(&pqueue->parallel.lock);

    while (!list_empty(&local_list)) {
        struct padata_priv *padata;

        padata = list_entry(local_list.next,
                    struct padata_priv, list);

        list_del_init(&padata->list);

        padata->parallel(padata);
    }

    local_bh_enable();
}

int padata_do_parallel(struct padata_instance *pinst,
               struct padata_priv *padata, int cb_cpu)
{
    int target_cpu, err;
    struct padata_parallel_queue *queue;
    struct parallel_data *pd;

    rcu_read_lock_bh();

    pd = rcu_dereference(pinst->pd);

    err = -EINVAL;
    if (!(pinst->flags & PADATA_INIT) || pinst->flags & PADATA_INVALID)
        goto out;

    if (!cpumask_test_cpu(cb_cpu, pd->cpumask.cbcpu))
        goto out;

    err =  -EBUSY;
    if ((pinst->flags & PADATA_RESET))
        goto out;

    if (atomic_read(&pd->refcnt) >= MAX_OBJ_NUM)
        goto out;

    err = 0;
    atomic_inc(&pd->refcnt);
    padata->pd = pd;
    padata->cb_cpu = cb_cpu;

    target_cpu = padata_cpu_hash(pd);
    queue = per_cpu_ptr(pd->pqueue, target_cpu);

    spin_lock(&queue->parallel.lock);
    list_add_tail(&padata->list, &queue->parallel.list);
    spin_unlock(&queue->parallel.lock);

    queue_work_on(target_cpu, pinst->wq, &queue->work);

out:
    rcu_read_unlock_bh();

    return err;
}
EXPORT_SYMBOL(padata_do_parallel);

/*
 * padata_get_next - Get the next object that needs serialization.
 *
 * Return values are:
 *
 * A pointer to the control struct of the next object that needs
 * serialization, if present in one of the percpu reorder queues.
 *
 * NULL, if all percpu reorder queues are empty.
 *
 * -EINPROGRESS, if the next object that needs serialization will
 *  be parallel processed by another cpu and is not yet present in
 *  the cpu's reorder queue.
 *
 * -ENODATA, if this cpu has to do the parallel processing for
 *  the next object.
 */
static struct padata_priv *padata_get_next(struct parallel_data *pd)
{
    int cpu, num_cpus;
    unsigned int next_nr, next_index;
    struct padata_parallel_queue *queue, *next_queue;
    struct padata_priv *padata;
    struct padata_list *reorder;

    num_cpus = cpumask_weight(pd->cpumask.pcpu);

    /*
     * Calculate the percpu reorder queue and the sequence
     * number of the next object.
     */
    next_nr = pd->processed;
    next_index = next_nr % num_cpus;
    cpu = padata_index_to_cpu(pd, next_index);
    next_queue = per_cpu_ptr(pd->pqueue, cpu);

    padata = NULL;

    reorder = &next_queue->reorder;

    if (!list_empty(&reorder->list)) {
        padata = list_entry(reorder->list.next,
                    struct padata_priv, list);

        spin_lock(&reorder->lock);
        list_del_init(&padata->list);
        atomic_dec(&pd->reorder_objects);
        spin_unlock(&reorder->lock);

        pd->processed++;

        goto out;
    }

    queue = per_cpu_ptr(pd->pqueue, smp_processor_id());
    if (queue->cpu_index == next_queue->cpu_index) {
        padata = ERR_PTR(-ENODATA);
        goto out;
    }

    padata = ERR_PTR(-EINPROGRESS);
out:
    return padata;
}

static void padata_reorder(struct parallel_data *pd)
{
    int cb_cpu;
    struct padata_priv *padata;
    struct padata_serial_queue *squeue;
    struct padata_instance *pinst = pd->pinst;

    /*
     * We need to ensure that only one cpu can work on dequeueing of
     * the reorder queue the time. Calculating in which percpu reorder
     * queue the next object will arrive takes some time. A spinlock
     * would be highly contended. Also it is not clear in which order
     * the objects arrive to the reorder queues. So a cpu could wait to
     * get the lock just to notice that there is nothing to do at the
     * moment. Therefore we use a trylock and let the holder of the lock
     * care for all the objects enqueued during the holdtime of the lock.
     */
    if (!spin_trylock_bh(&pd->lock))
        return;

    while (1) {
        padata = padata_get_next(pd);

        /*
         * All reorder queues are empty, or the next object that needs
         * serialization is parallel processed by another cpu and is
         * still on it's way to the cpu's reorder queue, nothing to
         * do for now.
         */
        if (!padata || PTR_ERR(padata) == -EINPROGRESS)
            break;

        /*
         * This cpu has to do the parallel processing of the next
         * object. It's waiting in the cpu's parallelization queue,
         * so exit immediately.
         */
        if (PTR_ERR(padata) == -ENODATA) {
            del_timer(&pd->timer);
            spin_unlock_bh(&pd->lock);
            return;
        }

        cb_cpu = padata->cb_cpu;
        squeue = per_cpu_ptr(pd->squeue, cb_cpu);

        spin_lock(&squeue->serial.lock);
        list_add_tail(&padata->list, &squeue->serial.list);
        spin_unlock(&squeue->serial.lock);

        queue_work_on(cb_cpu, pinst->wq, &squeue->work);
    }

    spin_unlock_bh(&pd->lock);

    /*
     * The next object that needs serialization might have arrived to
     * the reorder queues in the meantime, we will be called again
     * from the timer function if no one else cares for it.
     */
    if (atomic_read(&pd->reorder_objects)
            && !(pinst->flags & PADATA_RESET))
        mod_timer(&pd->timer, jiffies + HZ);
    else
        del_timer(&pd->timer);

    return;
}

static void padata_reorder_timer(unsigned long arg)
{
    struct parallel_data *pd = (struct parallel_data *)arg;

    padata_reorder(pd);
}

static void padata_serial_worker(struct work_struct *serial_work)
{
    struct padata_serial_queue *squeue;
    struct parallel_data *pd;
    LIST_HEAD(local_list);

    local_bh_disable();
    squeue = container_of(serial_work, struct padata_serial_queue, work);
    pd = squeue->pd;

    spin_lock(&squeue->serial.lock);
    list_replace_init(&squeue->serial.list, &local_list);
    spin_unlock(&squeue->serial.lock);

    while (!list_empty(&local_list)) {
        struct padata_priv *padata;

        padata = list_entry(local_list.next,
                    struct padata_priv, list);

        list_del_init(&padata->list);

        padata->serial(padata);
        atomic_dec(&pd->refcnt);
    }
    local_bh_enable();
}

void padata_do_serial(struct padata_priv *padata)
{
    int cpu;
    struct padata_parallel_queue *pqueue;
    struct parallel_data *pd;

    pd = padata->pd;

    cpu = get_cpu();
    pqueue = per_cpu_ptr(pd->pqueue, cpu);

    spin_lock(&pqueue->reorder.lock);
    atomic_inc(&pd->reorder_objects);
    list_add_tail(&padata->list, &pqueue->reorder.list);
    spin_unlock(&pqueue->reorder.lock);

    put_cpu();

    padata_reorder(pd);
}
EXPORT_SYMBOL(padata_do_serial);

static int padata_setup_cpumasks(struct parallel_data *pd,
                 const struct cpumask *pcpumask,
                 const struct cpumask *cbcpumask)
{
    if (!alloc_cpumask_var(&pd->cpumask.pcpu, GFP_KERNEL))
        return -ENOMEM;

    cpumask_and(pd->cpumask.pcpu, pcpumask, cpu_online_mask);
    if (!alloc_cpumask_var(&pd->cpumask.cbcpu, GFP_KERNEL)) {
        free_cpumask_var(pd->cpumask.cbcpu);
        return -ENOMEM;
    }

    cpumask_and(pd->cpumask.cbcpu, cbcpumask, cpu_online_mask);
    return 0;
}

static void __padata_list_init(struct padata_list *pd_list)
{
    INIT_LIST_HEAD(&pd_list->list);
    spin_lock_init(&pd_list->lock);
}

/* Initialize all percpu queues used by serial workers */
static void padata_init_squeues(struct parallel_data *pd)
{
    int cpu;
    struct padata_serial_queue *squeue;

    for_each_cpu(cpu, pd->cpumask.cbcpu) {
        squeue = per_cpu_ptr(pd->squeue, cpu);
        squeue->pd = pd;
        __padata_list_init(&squeue->serial);
        INIT_WORK(&squeue->work, padata_serial_worker);
    }
}

/* Initialize all percpu queues used by parallel workers */
static void padata_init_pqueues(struct parallel_data *pd)
{
    int cpu_index, cpu;
    struct padata_parallel_queue *pqueue;

    cpu_index = 0;
    for_each_cpu(cpu, pd->cpumask.pcpu) {
        pqueue = per_cpu_ptr(pd->pqueue, cpu);
        pqueue->pd = pd;
        pqueue->cpu_index = cpu_index;
        cpu_index++;

        __padata_list_init(&pqueue->reorder);
        __padata_list_init(&pqueue->parallel);
        INIT_WORK(&pqueue->work, padata_parallel_worker);
        atomic_set(&pqueue->num_obj, 0);
    }
}

/* Allocate and initialize the internal cpumask dependend resources. */
static struct parallel_data *padata_alloc_pd(struct padata_instance *pinst,
                         const struct cpumask *pcpumask,
                         const struct cpumask *cbcpumask)
{
    struct parallel_data *pd;

    pd = kzalloc(sizeof(struct parallel_data), GFP_KERNEL);
    if (!pd)
        goto err;

    pd->pqueue = alloc_percpu(struct padata_parallel_queue);
    if (!pd->pqueue)
        goto err_free_pd;

    pd->squeue = alloc_percpu(struct padata_serial_queue);
    if (!pd->squeue)
        goto err_free_pqueue;
    if (padata_setup_cpumasks(pd, pcpumask, cbcpumask) < 0)
        goto err_free_squeue;

    padata_init_pqueues(pd);
    padata_init_squeues(pd);
    setup_timer(&pd->timer, padata_reorder_timer, (unsigned long)pd);
    pd->seq_nr = 0;
    atomic_set(&pd->reorder_objects, 0);
    atomic_set(&pd->refcnt, 0);
    pd->pinst = pinst;
    spin_lock_init(&pd->lock);

    return pd;

err_free_squeue:
    free_percpu(pd->squeue);
err_free_pqueue:
    free_percpu(pd->pqueue);
err_free_pd:
    kfree(pd);
err:
    return NULL;
}

static void padata_free_pd(struct parallel_data *pd)
{
    free_cpumask_var(pd->cpumask.pcpu);
    free_cpumask_var(pd->cpumask.cbcpu);
    free_percpu(pd->pqueue);
    free_percpu(pd->squeue);
    kfree(pd);
}

/* Flush all objects out of the padata queues. */
static void padata_flush_queues(struct parallel_data *pd)
{
    int cpu;
    struct padata_parallel_queue *pqueue;
    struct padata_serial_queue *squeue;

    for_each_cpu(cpu, pd->cpumask.pcpu) {
        pqueue = per_cpu_ptr(pd->pqueue, cpu);
        flush_work(&pqueue->work);
    }

    del_timer_sync(&pd->timer);

    if (atomic_read(&pd->reorder_objects))
        padata_reorder(pd);

    for_each_cpu(cpu, pd->cpumask.cbcpu) {
        squeue = per_cpu_ptr(pd->squeue, cpu);
        flush_work(&squeue->work);
    }

    BUG_ON(atomic_read(&pd->refcnt) != 0);
}

static void __padata_start(struct padata_instance *pinst)
{
    pinst->flags |= PADATA_INIT;
}

static void __padata_stop(struct padata_instance *pinst)
{
    if (!(pinst->flags & PADATA_INIT))
        return;

    pinst->flags &= ~PADATA_INIT;

    synchronize_rcu();

    get_online_cpus();
    padata_flush_queues(pinst->pd);
    put_online_cpus();
}

/* Replace the internal control structure with a new one. */
static void padata_replace(struct padata_instance *pinst,
               struct parallel_data *pd_new)
{
    struct parallel_data *pd_old = pinst->pd;
    int notification_mask = 0;

    pinst->flags |= PADATA_RESET;

    rcu_assign_pointer(pinst->pd, pd_new);

    synchronize_rcu();

    if (!cpumask_equal(pd_old->cpumask.pcpu, pd_new->cpumask.pcpu))
        notification_mask |= PADATA_CPU_PARALLEL;
    if (!cpumask_equal(pd_old->cpumask.cbcpu, pd_new->cpumask.cbcpu))
        notification_mask |= PADATA_CPU_SERIAL;

    padata_flush_queues(pd_old);
    padata_free_pd(pd_old);

    if (notification_mask)
        blocking_notifier_call_chain(&pinst->cpumask_change_notifier,
                         notification_mask,
                         &pd_new->cpumask);

    pinst->flags &= ~PADATA_RESET;
}

int padata_register_cpumask_notifier(struct padata_instance *pinst,
                     struct notifier_block *nblock)
{
    return blocking_notifier_chain_register(&pinst->cpumask_change_notifier,
                        nblock);
}
EXPORT_SYMBOL(padata_register_cpumask_notifier);

int padata_unregister_cpumask_notifier(struct padata_instance *pinst,
                       struct notifier_block *nblock)
{
    return blocking_notifier_chain_unregister(
        &pinst->cpumask_change_notifier,
        nblock);
}
EXPORT_SYMBOL(padata_unregister_cpumask_notifier);


/* If cpumask contains no active cpu, we mark the instance as invalid. */
static bool padata_validate_cpumask(struct padata_instance *pinst,
                    const struct cpumask *cpumask)
{
    if (!cpumask_intersects(cpumask, cpu_online_mask)) {
        pinst->flags |= PADATA_INVALID;
        return false;
    }

    pinst->flags &= ~PADATA_INVALID;
    return true;
}

static int __padata_set_cpumasks(struct padata_instance *pinst,
                 cpumask_var_t pcpumask,
                 cpumask_var_t cbcpumask)
{
    int valid;
    struct parallel_data *pd;

    valid = padata_validate_cpumask(pinst, pcpumask);
    if (!valid) {
        __padata_stop(pinst);
        goto out_replace;
    }

    valid = padata_validate_cpumask(pinst, cbcpumask);
    if (!valid)
        __padata_stop(pinst);

out_replace:
    pd = padata_alloc_pd(pinst, pcpumask, cbcpumask);
    if (!pd)
        return -ENOMEM;

    cpumask_copy(pinst->cpumask.pcpu, pcpumask);
    cpumask_copy(pinst->cpumask.cbcpu, cbcpumask);

    padata_replace(pinst, pd);

    if (valid)
        __padata_start(pinst);

    return 0;
}

int padata_set_cpumasks(struct padata_instance *pinst, cpumask_var_t pcpumask,
            cpumask_var_t cbcpumask)
{
    int err;

    mutex_lock(&pinst->lock);
    get_online_cpus();

    err = __padata_set_cpumasks(pinst, pcpumask, cbcpumask);

    put_online_cpus();
    mutex_unlock(&pinst->lock);

    return err;

}
EXPORT_SYMBOL(padata_set_cpumasks);

int padata_set_cpumask(struct padata_instance *pinst, int cpumask_type,
               cpumask_var_t cpumask)
{
    struct cpumask *serial_mask, *parallel_mask;
    int err = -EINVAL;

    mutex_lock(&pinst->lock);
    get_online_cpus();

    switch (cpumask_type) {
    case PADATA_CPU_PARALLEL:
        serial_mask = pinst->cpumask.cbcpu;
        parallel_mask = cpumask;
        break;
    case PADATA_CPU_SERIAL:
        parallel_mask = pinst->cpumask.pcpu;
        serial_mask = cpumask;
        break;
    default:
         goto out;
    }

    err =  __padata_set_cpumasks(pinst, parallel_mask, serial_mask);

out:
    put_online_cpus();
    mutex_unlock(&pinst->lock);

    return err;
}
EXPORT_SYMBOL(padata_set_cpumask);

static int __padata_add_cpu(struct padata_instance *pinst, int cpu)
{
    struct parallel_data *pd;

    if (cpumask_test_cpu(cpu, cpu_online_mask)) {
        pd = padata_alloc_pd(pinst, pinst->cpumask.pcpu,
                     pinst->cpumask.cbcpu);
        if (!pd)
            return -ENOMEM;

        padata_replace(pinst, pd);

        if (padata_validate_cpumask(pinst, pinst->cpumask.pcpu) &&
            padata_validate_cpumask(pinst, pinst->cpumask.cbcpu))
            __padata_start(pinst);
    }

    return 0;
}

int padata_add_cpu(struct padata_instance *pinst, int cpu, int mask)
{
    int err;

    if (!(mask & (PADATA_CPU_SERIAL | PADATA_CPU_PARALLEL)))
        return -EINVAL;

    mutex_lock(&pinst->lock);

    get_online_cpus();
    if (mask & PADATA_CPU_SERIAL)
        cpumask_set_cpu(cpu, pinst->cpumask.cbcpu);
    if (mask & PADATA_CPU_PARALLEL)
        cpumask_set_cpu(cpu, pinst->cpumask.pcpu);

    err = __padata_add_cpu(pinst, cpu);
    put_online_cpus();

    mutex_unlock(&pinst->lock);

    return err;
}
EXPORT_SYMBOL(padata_add_cpu);

static int __padata_remove_cpu(struct padata_instance *pinst, int cpu)
{
    struct parallel_data *pd = NULL;

    if (cpumask_test_cpu(cpu, cpu_online_mask)) {

        if (!padata_validate_cpumask(pinst, pinst->cpumask.pcpu) ||
            !padata_validate_cpumask(pinst, pinst->cpumask.cbcpu))
            __padata_stop(pinst);

        pd = padata_alloc_pd(pinst, pinst->cpumask.pcpu,
                     pinst->cpumask.cbcpu);
        if (!pd)
            return -ENOMEM;

        padata_replace(pinst, pd);

        cpumask_clear_cpu(cpu, pd->cpumask.cbcpu);
        cpumask_clear_cpu(cpu, pd->cpumask.pcpu);
    }

    return 0;
}

int padata_remove_cpu(struct padata_instance *pinst, int cpu, int mask)
{
    int err;

    if (!(mask & (PADATA_CPU_SERIAL | PADATA_CPU_PARALLEL)))
        return -EINVAL;

    mutex_lock(&pinst->lock);

    get_online_cpus();
    if (mask & PADATA_CPU_SERIAL)
        cpumask_clear_cpu(cpu, pinst->cpumask.cbcpu);
    if (mask & PADATA_CPU_PARALLEL)
        cpumask_clear_cpu(cpu, pinst->cpumask.pcpu);

    err = __padata_remove_cpu(pinst, cpu);
    put_online_cpus();

    mutex_unlock(&pinst->lock);

    return err;
}
EXPORT_SYMBOL(padata_remove_cpu);

int padata_start(struct padata_instance *pinst)
{
    int err = 0;

    mutex_lock(&pinst->lock);

    if (pinst->flags & PADATA_INVALID)
        err =-EINVAL;

     __padata_start(pinst);

    mutex_unlock(&pinst->lock);

    return err;
}
EXPORT_SYMBOL(padata_start);

void padata_stop(struct padata_instance *pinst)
{
    mutex_lock(&pinst->lock);
    __padata_stop(pinst);
    mutex_unlock(&pinst->lock);
}
EXPORT_SYMBOL(padata_stop);

#ifdef CONFIG_HOTPLUG_CPU

static inline int pinst_has_cpu(struct padata_instance *pinst, int cpu)
{
    return cpumask_test_cpu(cpu, pinst->cpumask.pcpu) ||
        cpumask_test_cpu(cpu, pinst->cpumask.cbcpu);
}


static int padata_cpu_callback(struct notifier_block *nfb,
                   unsigned long action, void *hcpu)
{
    int err;
    struct padata_instance *pinst;
    int cpu = (unsigned long)hcpu;

    pinst = container_of(nfb, struct padata_instance, cpu_notifier);

    switch (action) {
    case CPU_ONLINE:
    case CPU_ONLINE_FROZEN:
        if (!pinst_has_cpu(pinst, cpu))
            break;
        mutex_lock(&pinst->lock);
        err = __padata_add_cpu(pinst, cpu);
        mutex_unlock(&pinst->lock);
        if (err)
            return notifier_from_errno(err);
        break;

    case CPU_DOWN_PREPARE:
    case CPU_DOWN_PREPARE_FROZEN:
        if (!pinst_has_cpu(pinst, cpu))
            break;
        mutex_lock(&pinst->lock);
        err = __padata_remove_cpu(pinst, cpu);
        mutex_unlock(&pinst->lock);
        if (err)
            return notifier_from_errno(err);
        break;

    case CPU_UP_CANCELED:
    case CPU_UP_CANCELED_FROZEN:
        if (!pinst_has_cpu(pinst, cpu))
            break;
        mutex_lock(&pinst->lock);
        __padata_remove_cpu(pinst, cpu);
        mutex_unlock(&pinst->lock);

    case CPU_DOWN_FAILED:
    case CPU_DOWN_FAILED_FROZEN:
        if (!pinst_has_cpu(pinst, cpu))
            break;
        mutex_lock(&pinst->lock);
        __padata_add_cpu(pinst, cpu);
        mutex_unlock(&pinst->lock);
    }

    return NOTIFY_OK;
}
#endif

static void __padata_free(struct padata_instance *pinst)
{
#ifdef CONFIG_HOTPLUG_CPU
    unregister_hotcpu_notifier(&pinst->cpu_notifier);
#endif

    padata_stop(pinst);
    padata_free_pd(pinst->pd);
    free_cpumask_var(pinst->cpumask.pcpu);
    free_cpumask_var(pinst->cpumask.cbcpu);
    kfree(pinst);
}

#define kobj2pinst(_kobj)                   \
    container_of(_kobj, struct padata_instance, kobj)
#define attr2pentry(_attr)                  \
    container_of(_attr, struct padata_sysfs_entry, attr)

static void padata_sysfs_release(struct kobject *kobj)
{
    struct padata_instance *pinst = kobj2pinst(kobj);
    __padata_free(pinst);
}

struct padata_sysfs_entry {
    struct attribute attr;
    ssize_t (*show)(struct padata_instance *, struct attribute *, char *);
    ssize_t (*store)(struct padata_instance *, struct attribute *,
             const char *, size_t);
};

static ssize_t show_cpumask(struct padata_instance *pinst,
                struct attribute *attr,  char *buf)
{
    struct cpumask *cpumask;
    ssize_t len;

    mutex_lock(&pinst->lock);
    if (!strcmp(attr->name, "serial_cpumask"))
        cpumask = pinst->cpumask.cbcpu;
    else
        cpumask = pinst->cpumask.pcpu;

    len = bitmap_scnprintf(buf, PAGE_SIZE, cpumask_bits(cpumask),
                   nr_cpu_ids);
    if (PAGE_SIZE - len < 2)
        len = -EINVAL;
    else
        len += sprintf(buf + len, "\n");

    mutex_unlock(&pinst->lock);
    return len;
}

static ssize_t store_cpumask(struct padata_instance *pinst,
                 struct attribute *attr,
                 const char *buf, size_t count)
{
    cpumask_var_t new_cpumask;
    ssize_t ret;
    int mask_type;

    if (!alloc_cpumask_var(&new_cpumask, GFP_KERNEL))
        return -ENOMEM;

    ret = bitmap_parse(buf, count, cpumask_bits(new_cpumask),
               nr_cpumask_bits);
    if (ret < 0)
        goto out;

    mask_type = !strcmp(attr->name, "serial_cpumask") ?
        PADATA_CPU_SERIAL : PADATA_CPU_PARALLEL;
    ret = padata_set_cpumask(pinst, mask_type, new_cpumask);
    if (!ret)
        ret = count;

out:
    free_cpumask_var(new_cpumask);
    return ret;
}

#define PADATA_ATTR_RW(_name, _show_name, _store_name)      \
    static struct padata_sysfs_entry _name##_attr =     \
        __ATTR(_name, 0644, _show_name, _store_name)
#define PADATA_ATTR_RO(_name, _show_name)       \
    static struct padata_sysfs_entry _name##_attr = \
        __ATTR(_name, 0400, _show_name, NULL)

PADATA_ATTR_RW(serial_cpumask, show_cpumask, store_cpumask);
PADATA_ATTR_RW(parallel_cpumask, show_cpumask, store_cpumask);

/*
 * Padata sysfs provides the following objects:
 * serial_cpumask   [RW] - cpumask for serial workers
 * parallel_cpumask [RW] - cpumask for parallel workers
 */
static struct attribute *padata_default_attrs[] = {
    &serial_cpumask_attr.attr,
    &parallel_cpumask_attr.attr,
    NULL,
};

static ssize_t padata_sysfs_show(struct kobject *kobj,
                 struct attribute *attr, char *buf)
{
    struct padata_instance *pinst;
    struct padata_sysfs_entry *pentry;
    ssize_t ret = -EIO;

    pinst = kobj2pinst(kobj);
    pentry = attr2pentry(attr);
    if (pentry->show)
        ret = pentry->show(pinst, attr, buf);

    return ret;
}

static ssize_t padata_sysfs_store(struct kobject *kobj, struct attribute *attr,
                  const char *buf, size_t count)
{
    struct padata_instance *pinst;
    struct padata_sysfs_entry *pentry;
    ssize_t ret = -EIO;

    pinst = kobj2pinst(kobj);
    pentry = attr2pentry(attr);
    if (pentry->show)
        ret = pentry->store(pinst, attr, buf, count);

    return ret;
}

static const struct sysfs_ops padata_sysfs_ops = {
    .show = padata_sysfs_show,
    .store = padata_sysfs_store,
};

static struct kobj_type padata_attr_type = {
    .sysfs_ops = &padata_sysfs_ops,
    .default_attrs = padata_default_attrs,
    .release = padata_sysfs_release,
};

struct padata_instance *padata_alloc_possible(struct workqueue_struct *wq)
{
    return padata_alloc(wq, cpu_possible_mask, cpu_possible_mask);
}
EXPORT_SYMBOL(padata_alloc_possible);

struct padata_instance *padata_alloc(struct workqueue_struct *wq,
                     const struct cpumask *pcpumask,
                     const struct cpumask *cbcpumask)
{
    struct padata_instance *pinst;
    struct parallel_data *pd = NULL;

    pinst = kzalloc(sizeof(struct padata_instance), GFP_KERNEL);
    if (!pinst)
        goto err;

    get_online_cpus();
    if (!alloc_cpumask_var(&pinst->cpumask.pcpu, GFP_KERNEL))
        goto err_free_inst;
    if (!alloc_cpumask_var(&pinst->cpumask.cbcpu, GFP_KERNEL)) {
        free_cpumask_var(pinst->cpumask.pcpu);
        goto err_free_inst;
    }
    if (!padata_validate_cpumask(pinst, pcpumask) ||
        !padata_validate_cpumask(pinst, cbcpumask))
        goto err_free_masks;

    pd = padata_alloc_pd(pinst, pcpumask, cbcpumask);
    if (!pd)
        goto err_free_masks;

    rcu_assign_pointer(pinst->pd, pd);

    pinst->wq = wq;

    cpumask_copy(pinst->cpumask.pcpu, pcpumask);
    cpumask_copy(pinst->cpumask.cbcpu, cbcpumask);

    pinst->flags = 0;

#ifdef CONFIG_HOTPLUG_CPU
    pinst->cpu_notifier.notifier_call = padata_cpu_callback;
    pinst->cpu_notifier.priority = 0;
    register_hotcpu_notifier(&pinst->cpu_notifier);
#endif

    put_online_cpus();

    BLOCKING_INIT_NOTIFIER_HEAD(&pinst->cpumask_change_notifier);
    kobject_init(&pinst->kobj, &padata_attr_type);
    mutex_init(&pinst->lock);

    return pinst;

err_free_masks:
    free_cpumask_var(pinst->cpumask.pcpu);
    free_cpumask_var(pinst->cpumask.cbcpu);
err_free_inst:
    kfree(pinst);
    put_online_cpus();
err:
    return NULL;
}
EXPORT_SYMBOL(padata_alloc);

void padata_free(struct padata_instance *pinst)
{
    kobject_put(&pinst->kobj);
}
EXPORT_SYMBOL(padata_free);