ftrace: Avoid potential division by zero in function profiler

[mirror_ubuntu-bionic-kernel.git] / kernel / padata.c

/*
 * 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 <steffen.klassert@secunet.com>
 *
 * 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>
#include <linux/module.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)
{
        unsigned int seq_nr;
        int cpu_index;

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

        seq_nr = atomic_inc_return(&pd->seq_nr);
        cpu_index = seq_nr % cpumask_weight(pd->cpumask.pcpu);

        return padata_index_to_cpu(pd, cpu_index);
}

static void padata_parallel_worker(struct work_struct *parallel_work)
{
        struct padata_parallel_queue *pqueue;
        LIST_HEAD(local_list);

        local_bh_disable();
        pqueue = container_of(parallel_work,
                              struct padata_parallel_queue, work);

        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();
}

/**
 * padata_do_parallel - padata parallelization function
 *
 * @pinst: padata instance
 * @padata: object to be parallelized
 * @cb_cpu: cpu the serialization callback function will run on,
 *          must be in the serial cpumask of padata(i.e. cpumask.cbcpu).
 *
 * The parallelization callback function will run with BHs off.
 * Note: Every object which is parallelized by padata_do_parallel
 * must be seen by padata_do_serial.
 */
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_bh(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);
        padata->cpu = target_cpu;
        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.
 *
 * -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 *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);

        reorder = &next_queue->reorder;

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

                list_del_init(&padata->list);
                atomic_dec(&pd->reorder_objects);

                pd->processed++;

                spin_unlock(&reorder->lock);
                goto out;
        }
        spin_unlock(&reorder->lock);

        if (__this_cpu_read(pd->pqueue->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);

                /*
                 * If 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 (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.
         *
         * Ensure reorder_objects is read after pd->lock is dropped so we see
         * an increment from another task in padata_do_serial.  Pairs with
         * smp_mb__after_atomic in padata_do_serial.
         */
        smp_mb();
        if (atomic_read(&pd->reorder_objects)
                        && !(pinst->flags & PADATA_RESET))
                mod_timer(&pd->timer, jiffies + HZ);
        else
                del_timer(&pd->timer);

        return;
}

static void invoke_padata_reorder(struct work_struct *work)
{
        struct padata_parallel_queue *pqueue;
        struct parallel_data *pd;

        local_bh_disable();
        pqueue = container_of(work, struct padata_parallel_queue, reorder_work);
        pd = pqueue->pd;
        padata_reorder(pd);
        local_bh_enable();
}

static void padata_reorder_timer(struct timer_list *t)
{
        struct parallel_data *pd = from_timer(pd, t, timer);
        unsigned int weight;
        int target_cpu, cpu;

        cpu = get_cpu();

        /* We don't lock pd here to not interfere with parallel processing
         * padata_reorder() calls on other CPUs. We just need any CPU out of
         * the cpumask.pcpu set. It would be nice if it's the right one but
         * it doesn't matter if we're off to the next one by using an outdated
         * pd->processed value.
         */
        weight = cpumask_weight(pd->cpumask.pcpu);
        target_cpu = padata_index_to_cpu(pd, pd->processed % weight);

        /* ensure to call the reorder callback on the correct CPU */
        if (cpu != target_cpu) {
                struct padata_parallel_queue *pqueue;
                struct padata_instance *pinst;

                /* The timer function is serialized wrt itself -- no locking
                 * needed.
                 */
                pinst = pd->pinst;
                pqueue = per_cpu_ptr(pd->pqueue, target_cpu);
                queue_work_on(target_cpu, pinst->wq, &pqueue->reorder_work);
        } else {
                padata_reorder(pd);
        }

        put_cpu();
}

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();
}

/**
 * padata_do_serial - padata serialization function
 *
 * @padata: object to be serialized.
 *
 * padata_do_serial must be called for every parallelized object.
 * The serialization callback function will run with BHs off.
 */
void padata_do_serial(struct padata_priv *padata)
{
        int cpu;
        struct padata_parallel_queue *pqueue;
        struct parallel_data *pd;
        int reorder_via_wq = 0;

        pd = padata->pd;

        cpu = get_cpu();

        /* We need to run on the same CPU padata_do_parallel(.., padata, ..)
         * was called on -- or, at least, enqueue the padata object into the
         * correct per-cpu queue.
         */
        if (cpu != padata->cpu) {
                reorder_via_wq = 1;
                cpu = padata->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);

        /*
         * Ensure the atomic_inc of reorder_objects above is ordered correctly
         * with the trylock of pd->lock in padata_reorder.  Pairs with smp_mb
         * in padata_reorder.
         */
        smp_mb__after_atomic();

        put_cpu();

        /* If we're running on the wrong CPU, call padata_reorder() via a
         * kernel worker.
         */
        if (reorder_via_wq)
                queue_work_on(cpu, pd->pinst->wq, &pqueue->reorder_work);
        else
                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.pcpu);
                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_possible_cpu(cpu) {
                pqueue = per_cpu_ptr(pd->pqueue, cpu);

                if (!cpumask_test_cpu(cpu, pd->cpumask.pcpu)) {
                        pqueue->cpu_index = -1;
                        continue;
                }

                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);
                INIT_WORK(&pqueue->reorder_work, invoke_padata_reorder);
                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);
        timer_setup(&pd->timer, padata_reorder_timer, 0);
        atomic_set(&pd->seq_nr, -1);
        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;
}

/**
 * padata_register_cpumask_notifier - Registers a notifier that will be called
 *                             if either pcpu or cbcpu or both cpumasks change.
 *
 * @pinst: A poineter to padata instance
 * @nblock: A pointer to notifier block.
 */
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);

/**
 * padata_unregister_cpumask_notifier - Unregisters cpumask notifier
 *        registered earlier  using padata_register_cpumask_notifier
 *
 * @pinst: A pointer to data instance.
 * @nlock: A pointer to notifier block.
 */
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;
}

/**
 * padata_set_cpumask: Sets specified by @cpumask_type cpumask to the value
 *                     equivalent to @cpumask.
 *
 * @pinst: padata instance
 * @cpumask_type: PADATA_CPU_SERIAL or PADATA_CPU_PARALLEL corresponding
 *                to parallel and serial cpumasks respectively.
 * @cpumask: the cpumask to use
 */
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);

/**
 * padata_start - start the parallel processing
 *
 * @pinst: padata instance to start
 */
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);

/**
 * padata_stop - stop the parallel processing
 *
 * @pinst: padata instance to stop
 */
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 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;
}

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;
}

 /**
 * padata_remove_cpu - remove a cpu from the one or both(serial and parallel)
 *                     padata cpumasks.
 *
 * @pinst: padata instance
 * @cpu: cpu to remove
 * @mask: bitmask specifying from which cpumask @cpu should be removed
 *        The @mask may be any combination of the following flags:
 *          PADATA_CPU_SERIAL   - serial cpumask
 *          PADATA_CPU_PARALLEL - parallel cpumask
 */
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);

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_online(unsigned int cpu, struct hlist_node *node)
{
        struct padata_instance *pinst;
        int ret;

        pinst = hlist_entry_safe(node, struct padata_instance, node);
        if (!pinst_has_cpu(pinst, cpu))
                return 0;

        mutex_lock(&pinst->lock);
        ret = __padata_add_cpu(pinst, cpu);
        mutex_unlock(&pinst->lock);
        return ret;
}

static int padata_cpu_prep_down(unsigned int cpu, struct hlist_node *node)
{
        struct padata_instance *pinst;
        int ret;

        pinst = hlist_entry_safe(node, struct padata_instance, node);
        if (!pinst_has_cpu(pinst, cpu))
                return 0;

        mutex_lock(&pinst->lock);
        ret = __padata_remove_cpu(pinst, cpu);
        mutex_unlock(&pinst->lock);
        return ret;
}

static enum cpuhp_state hp_online;
#endif

static void __padata_free(struct padata_instance *pinst)
{
#ifdef CONFIG_HOTPLUG_CPU
        cpuhp_state_remove_instance_nocalls(hp_online, &pinst->node);
#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 = snprintf(buf, PAGE_SIZE, "%*pb\n",
                       nr_cpu_ids, cpumask_bits(cpumask));
        mutex_unlock(&pinst->lock);
        return len < PAGE_SIZE ? len : -EINVAL;
}

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,
};

/**
 * padata_alloc - allocate and initialize a padata instance and specify
 *                cpumasks for serial and parallel workers.
 *
 * @wq: workqueue to use for the allocated padata instance
 * @pcpumask: cpumask that will be used for padata parallelization
 * @cbcpumask: cpumask that will be used for padata serialization
 *
 * Must be called from a cpus_read_lock() protected region
 */
static 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;

        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;

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

#ifdef CONFIG_HOTPLUG_CPU
        cpuhp_state_add_instance_nocalls_cpuslocked(hp_online, &pinst->node);
#endif
        return pinst;

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

/**
 * padata_alloc_possible - Allocate and initialize padata instance.
 *                         Use the cpu_possible_mask for serial and
 *                         parallel workers.
 *
 * @wq: workqueue to use for the allocated padata instance
 *
 * Must be called from a cpus_read_lock() protected region
 */
struct padata_instance *padata_alloc_possible(struct workqueue_struct *wq)
{
        lockdep_assert_cpus_held();
        return padata_alloc(wq, cpu_possible_mask, cpu_possible_mask);
}
EXPORT_SYMBOL(padata_alloc_possible);

/**
 * padata_free - free a padata instance
 *
 * @padata_inst: padata instance to free
 */
void padata_free(struct padata_instance *pinst)
{
        kobject_put(&pinst->kobj);
}
EXPORT_SYMBOL(padata_free);

#ifdef CONFIG_HOTPLUG_CPU

static __init int padata_driver_init(void)
{
        int ret;

        ret = cpuhp_setup_state_multi(CPUHP_AP_ONLINE_DYN, "padata:online",
                                      padata_cpu_online,
                                      padata_cpu_prep_down);
        if (ret < 0)
                return ret;
        hp_online = ret;
        return 0;
}
module_init(padata_driver_init);

static __exit void padata_driver_exit(void)
{
        cpuhp_remove_multi_state(hp_online);
}
module_exit(padata_driver_exit);
#endif