Merge tag 'trace-printf-v6.13' of git://git.kernel.org/pub/scm/linux/kernel/git/trace...

[drm/drm-misc.git] / kernel / padata.c

// SPDX-License-Identifier: GPL-2.0
/*
 * padata.c - generic interface to process data streams in parallel
 *
 * See Documentation/core-api/padata.rst for more information.
 *
 * Copyright (C) 2008, 2009 secunet Security Networks AG
 * Copyright (C) 2008, 2009 Steffen Klassert <steffen.klassert@secunet.com>
 *
 * Copyright (c) 2020 Oracle and/or its affiliates.
 * Author: Daniel Jordan <daniel.m.jordan@oracle.com>
 */

#include <linux/completion.h>
#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 PADATA_WORK_ONSTACK     1       /* Work's memory is on stack */

struct padata_work {
        struct work_struct      pw_work;
        struct list_head        pw_list;  /* padata_free_works linkage */
        void                    *pw_data;
};

static DEFINE_SPINLOCK(padata_works_lock);
static struct padata_work *padata_works;
static LIST_HEAD(padata_free_works);

struct padata_mt_job_state {
        spinlock_t              lock;
        struct completion       completion;
        struct padata_mt_job    *job;
        int                     nworks;
        int                     nworks_fini;
        unsigned long           chunk_size;
};

static void padata_free_pd(struct parallel_data *pd);
static void __init padata_mt_helper(struct work_struct *work);

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)
{
        /*
         * Hash the sequence numbers to the cpus by taking
         * seq_nr mod. number of cpus in use.
         */
        int cpu_index = seq_nr % cpumask_weight(pd->cpumask.pcpu);

        return padata_index_to_cpu(pd, cpu_index);
}

static struct padata_work *padata_work_alloc(void)
{
        struct padata_work *pw;

        lockdep_assert_held(&padata_works_lock);

        if (list_empty(&padata_free_works))
                return NULL;    /* No more work items allowed to be queued. */

        pw = list_first_entry(&padata_free_works, struct padata_work, pw_list);
        list_del(&pw->pw_list);
        return pw;
}

/*
 * This function is marked __ref because this function may be optimized in such
 * a way that it directly refers to work_fn's address, which causes modpost to
 * complain when work_fn is marked __init. This scenario was observed with clang
 * LTO, where padata_work_init() was optimized to refer directly to
 * padata_mt_helper() because the calls to padata_work_init() with other work_fn
 * values were eliminated or inlined.
 */
static void __ref padata_work_init(struct padata_work *pw, work_func_t work_fn,
                                   void *data, int flags)
{
        if (flags & PADATA_WORK_ONSTACK)
                INIT_WORK_ONSTACK(&pw->pw_work, work_fn);
        else
                INIT_WORK(&pw->pw_work, work_fn);
        pw->pw_data = data;
}

static int __init padata_work_alloc_mt(int nworks, void *data,
                                       struct list_head *head)
{
        int i;

        spin_lock_bh(&padata_works_lock);
        /* Start at 1 because the current task participates in the job. */
        for (i = 1; i < nworks; ++i) {
                struct padata_work *pw = padata_work_alloc();

                if (!pw)
                        break;
                padata_work_init(pw, padata_mt_helper, data, 0);
                list_add(&pw->pw_list, head);
        }
        spin_unlock_bh(&padata_works_lock);

        return i;
}

static void padata_work_free(struct padata_work *pw)
{
        lockdep_assert_held(&padata_works_lock);
        list_add(&pw->pw_list, &padata_free_works);
}

static void __init padata_works_free(struct list_head *works)
{
        struct padata_work *cur, *next;

        if (list_empty(works))
                return;

        spin_lock_bh(&padata_works_lock);
        list_for_each_entry_safe(cur, next, works, pw_list) {
                list_del(&cur->pw_list);
                padata_work_free(cur);
        }
        spin_unlock_bh(&padata_works_lock);
}

static void padata_parallel_worker(struct work_struct *parallel_work)
{
        struct padata_work *pw = container_of(parallel_work, struct padata_work,
                                              pw_work);
        struct padata_priv *padata = pw->pw_data;

        local_bh_disable();
        padata->parallel(padata);
        spin_lock(&padata_works_lock);
        padata_work_free(pw);
        spin_unlock(&padata_works_lock);
        local_bh_enable();
}

/**
 * padata_do_parallel - padata parallelization function
 *
 * @ps: padatashell
 * @padata: object to be parallelized
 * @cb_cpu: pointer to the CPU that the serialization callback function should
 *          run on.  If it's not in the serial cpumask of @pinst
 *          (i.e. cpumask.cbcpu), this function selects a fallback CPU and if
 *          none found, returns -EINVAL.
 *
 * 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.
 *
 * Return: 0 on success or else negative error code.
 */
int padata_do_parallel(struct padata_shell *ps,
                       struct padata_priv *padata, int *cb_cpu)
{
        struct padata_instance *pinst = ps->pinst;
        int i, cpu, cpu_index, err;
        struct parallel_data *pd;
        struct padata_work *pw;

        rcu_read_lock_bh();

        pd = rcu_dereference_bh(ps->pd);

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

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

                /* Select an alternate fallback CPU and notify the caller. */
                cpu_index = *cb_cpu % cpumask_weight(pd->cpumask.cbcpu);

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

                *cb_cpu = cpu;
        }

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

        refcount_inc(&pd->refcnt);
        padata->pd = pd;
        padata->cb_cpu = *cb_cpu;

        spin_lock(&padata_works_lock);
        padata->seq_nr = ++pd->seq_nr;
        pw = padata_work_alloc();
        spin_unlock(&padata_works_lock);

        if (!pw) {
                /* Maximum works limit exceeded, run in the current task. */
                padata->parallel(padata);
        }

        rcu_read_unlock_bh();

        if (pw) {
                padata_work_init(pw, padata_parallel_worker, padata, 0);
                queue_work(pinst->parallel_wq, &pw->pw_work);
        }

        return 0;
out:
        rcu_read_unlock_bh();

        return err;
}
EXPORT_SYMBOL(padata_do_parallel);

/*
 * padata_find_next - Find the next object that needs serialization.
 *
 * Return:
 * * A pointer to the control struct of the next object that needs
 *   serialization, if present in one of the percpu reorder queues.
 * * NULL, 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.
 */
static struct padata_priv *padata_find_next(struct parallel_data *pd,
                                            bool remove_object)
{
        struct padata_priv *padata;
        struct padata_list *reorder;
        int cpu = pd->cpu;

        reorder = per_cpu_ptr(pd->reorder_list, cpu);

        spin_lock(&reorder->lock);
        if (list_empty(&reorder->list)) {
                spin_unlock(&reorder->lock);
                return NULL;
        }

        padata = list_entry(reorder->list.next, struct padata_priv, list);

        /*
         * Checks the rare case where two or more parallel jobs have hashed to
         * the same CPU and one of the later ones finishes first.
         */
        if (padata->seq_nr != pd->processed) {
                spin_unlock(&reorder->lock);
                return NULL;
        }

        if (remove_object) {
                list_del_init(&padata->list);
                ++pd->processed;
                pd->cpu = cpumask_next_wrap(cpu, pd->cpumask.pcpu, -1, false);
        }

        spin_unlock(&reorder->lock);
        return padata;
}

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

        /*
         * 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_find_next(pd, true);

                /*
                 * 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 (!padata)
                        break;

                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->serial_wq, &squeue->work);
        }

        spin_unlock_bh(&pd->lock);

        /*
         * The next object that needs serialization might have arrived to
         * the reorder queues in the meantime.
         *
         * Ensure reorder queue is read after pd->lock is dropped so we see
         * new objects from another task in padata_do_serial.  Pairs with
         * smp_mb in padata_do_serial.
         */
        smp_mb();

        reorder = per_cpu_ptr(pd->reorder_list, pd->cpu);
        if (!list_empty(&reorder->list) && padata_find_next(pd, false))
                queue_work(pinst->serial_wq, &pd->reorder_work);
}

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

        local_bh_disable();
        pd = container_of(work, struct parallel_data, reorder_work);
        padata_reorder(pd);
        local_bh_enable();
}

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

        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);

        cnt = 0;

        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);
                cnt++;
        }
        local_bh_enable();

        if (refcount_sub_and_test(cnt, &pd->refcnt))
                padata_free_pd(pd);
}

/**
 * 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)
{
        struct parallel_data *pd = padata->pd;
        int hashed_cpu = padata_cpu_hash(pd, padata->seq_nr);
        struct padata_list *reorder = per_cpu_ptr(pd->reorder_list, hashed_cpu);
        struct padata_priv *cur;
        struct list_head *pos;

        spin_lock(&reorder->lock);
        /* Sort in ascending order of sequence number. */
        list_for_each_prev(pos, &reorder->list) {
                cur = list_entry(pos, struct padata_priv, list);
                /* Compare by difference to consider integer wrap around */
                if ((signed int)(cur->seq_nr - padata->seq_nr) < 0)
                        break;
        }
        list_add(&padata->list, pos);
        spin_unlock(&reorder->lock);

        /*
         * Ensure the addition to the reorder list is ordered correctly
         * with the trylock of pd->lock in padata_reorder.  Pairs with smp_mb
         * in padata_reorder.
         */
        smp_mb();

        padata_reorder(pd);
}
EXPORT_SYMBOL(padata_do_serial);

static int padata_setup_cpumasks(struct padata_instance *pinst)
{
        struct workqueue_attrs *attrs;
        int err;

        attrs = alloc_workqueue_attrs();
        if (!attrs)
                return -ENOMEM;

        /* Restrict parallel_wq workers to pd->cpumask.pcpu. */
        cpumask_copy(attrs->cpumask, pinst->cpumask.pcpu);
        err = apply_workqueue_attrs(pinst->parallel_wq, attrs);
        free_workqueue_attrs(attrs);

        return err;
}

static void __init padata_mt_helper(struct work_struct *w)
{
        struct padata_work *pw = container_of(w, struct padata_work, pw_work);
        struct padata_mt_job_state *ps = pw->pw_data;
        struct padata_mt_job *job = ps->job;
        bool done;

        spin_lock(&ps->lock);

        while (job->size > 0) {
                unsigned long start, size, end;

                start = job->start;
                /* So end is chunk size aligned if enough work remains. */
                size = roundup(start + 1, ps->chunk_size) - start;
                size = min(size, job->size);
                end = start + size;

                job->start = end;
                job->size -= size;

                spin_unlock(&ps->lock);
                job->thread_fn(start, end, job->fn_arg);
                spin_lock(&ps->lock);
        }

        ++ps->nworks_fini;
        done = (ps->nworks_fini == ps->nworks);
        spin_unlock(&ps->lock);

        if (done)
                complete(&ps->completion);
}

/**
 * padata_do_multithreaded - run a multithreaded job
 * @job: Description of the job.
 *
 * See the definition of struct padata_mt_job for more details.
 */
void __init padata_do_multithreaded(struct padata_mt_job *job)
{
        /* In case threads finish at different times. */
        static const unsigned long load_balance_factor = 4;
        struct padata_work my_work, *pw;
        struct padata_mt_job_state ps;
        LIST_HEAD(works);
        int nworks, nid;
        static atomic_t last_used_nid __initdata;

        if (job->size == 0)
                return;

        /* Ensure at least one thread when size < min_chunk. */
        nworks = max(job->size / max(job->min_chunk, job->align), 1ul);
        nworks = min(nworks, job->max_threads);

        if (nworks == 1) {
                /* Single thread, no coordination needed, cut to the chase. */
                job->thread_fn(job->start, job->start + job->size, job->fn_arg);
                return;
        }

        spin_lock_init(&ps.lock);
        init_completion(&ps.completion);
        ps.job         = job;
        ps.nworks      = padata_work_alloc_mt(nworks, &ps, &works);
        ps.nworks_fini = 0;

        /*
         * Chunk size is the amount of work a helper does per call to the
         * thread function.  Load balance large jobs between threads by
         * increasing the number of chunks, guarantee at least the minimum
         * chunk size from the caller, and honor the caller's alignment.
         * Ensure chunk_size is at least 1 to prevent divide-by-0
         * panic in padata_mt_helper().
         */
        ps.chunk_size = job->size / (ps.nworks * load_balance_factor);
        ps.chunk_size = max(ps.chunk_size, job->min_chunk);
        ps.chunk_size = max(ps.chunk_size, 1ul);
        ps.chunk_size = roundup(ps.chunk_size, job->align);

        list_for_each_entry(pw, &works, pw_list)
                if (job->numa_aware) {
                        int old_node = atomic_read(&last_used_nid);

                        do {
                                nid = next_node_in(old_node, node_states[N_CPU]);
                        } while (!atomic_try_cmpxchg(&last_used_nid, &old_node, nid));
                        queue_work_node(nid, system_unbound_wq, &pw->pw_work);
                } else {
                        queue_work(system_unbound_wq, &pw->pw_work);
                }

        /* Use the current thread, which saves starting a workqueue worker. */
        padata_work_init(&my_work, padata_mt_helper, &ps, PADATA_WORK_ONSTACK);
        padata_mt_helper(&my_work.pw_work);

        /* Wait for all the helpers to finish. */
        wait_for_completion(&ps.completion);

        destroy_work_on_stack(&my_work.pw_work);
        padata_works_free(&works);
}

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 per-CPU reorder lists */
static void padata_init_reorder_list(struct parallel_data *pd)
{
        int cpu;
        struct padata_list *list;

        for_each_cpu(cpu, pd->cpumask.pcpu) {
                list = per_cpu_ptr(pd->reorder_list, cpu);
                __padata_list_init(list);
        }
}

/* Allocate and initialize the internal cpumask dependend resources. */
static struct parallel_data *padata_alloc_pd(struct padata_shell *ps)
{
        struct padata_instance *pinst = ps->pinst;
        struct parallel_data *pd;

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

        pd->reorder_list = alloc_percpu(struct padata_list);
        if (!pd->reorder_list)
                goto err_free_pd;

        pd->squeue = alloc_percpu(struct padata_serial_queue);
        if (!pd->squeue)
                goto err_free_reorder_list;

        pd->ps = ps;

        if (!alloc_cpumask_var(&pd->cpumask.pcpu, GFP_KERNEL))
                goto err_free_squeue;
        if (!alloc_cpumask_var(&pd->cpumask.cbcpu, GFP_KERNEL))
                goto err_free_pcpu;

        cpumask_and(pd->cpumask.pcpu, pinst->cpumask.pcpu, cpu_online_mask);
        cpumask_and(pd->cpumask.cbcpu, pinst->cpumask.cbcpu, cpu_online_mask);

        padata_init_reorder_list(pd);
        padata_init_squeues(pd);
        pd->seq_nr = -1;
        refcount_set(&pd->refcnt, 1);
        spin_lock_init(&pd->lock);
        pd->cpu = cpumask_first(pd->cpumask.pcpu);
        INIT_WORK(&pd->reorder_work, invoke_padata_reorder);

        return pd;

err_free_pcpu:
        free_cpumask_var(pd->cpumask.pcpu);
err_free_squeue:
        free_percpu(pd->squeue);
err_free_reorder_list:
        free_percpu(pd->reorder_list);
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->reorder_list);
        free_percpu(pd->squeue);
        kfree(pd);
}

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();
}

/* Replace the internal control structure with a new one. */
static int padata_replace_one(struct padata_shell *ps)
{
        struct parallel_data *pd_new;

        pd_new = padata_alloc_pd(ps);
        if (!pd_new)
                return -ENOMEM;

        ps->opd = rcu_dereference_protected(ps->pd, 1);
        rcu_assign_pointer(ps->pd, pd_new);

        return 0;
}

static int padata_replace(struct padata_instance *pinst)
{
        struct padata_shell *ps;
        int err = 0;

        pinst->flags |= PADATA_RESET;

        list_for_each_entry(ps, &pinst->pslist, list) {
                err = padata_replace_one(ps);
                if (err)
                        break;
        }

        synchronize_rcu();

        list_for_each_entry_continue_reverse(ps, &pinst->pslist, list)
                if (refcount_dec_and_test(&ps->opd->refcnt))
                        padata_free_pd(ps->opd);

        pinst->flags &= ~PADATA_RESET;

        return err;
}

/* 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;
        int err;

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

        err = padata_setup_cpumasks(pinst) ?: padata_replace(pinst);

        if (valid)
                __padata_start(pinst);

        return err;
}

/**
 * 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
 *
 * Return: 0 on success or negative error code
 */
int padata_set_cpumask(struct padata_instance *pinst, int cpumask_type,
                       cpumask_var_t cpumask)
{
        struct cpumask *serial_mask, *parallel_mask;
        int err = -EINVAL;

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

        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:
        mutex_unlock(&pinst->lock);
        cpus_read_unlock();

        return err;
}
EXPORT_SYMBOL(padata_set_cpumask);

#ifdef CONFIG_HOTPLUG_CPU

static int __padata_add_cpu(struct padata_instance *pinst, int cpu)
{
        int err = 0;

        if (cpumask_test_cpu(cpu, cpu_online_mask)) {
                err = padata_replace(pinst);

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

        return err;
}

static int __padata_remove_cpu(struct padata_instance *pinst, int cpu)
{
        int err = 0;

        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);

                err = padata_replace(pinst);
        }

        return err;
}

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

        pinst = hlist_entry_safe(node, struct padata_instance, cpu_dead_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(CPUHP_PADATA_DEAD,
                                            &pinst->cpu_dead_node);
        cpuhp_state_remove_instance_nocalls(hp_online, &pinst->cpu_online_node);
#endif

        WARN_ON(!list_empty(&pinst->pslist));

        free_cpumask_var(pinst->cpumask.pcpu);
        free_cpumask_var(pinst->cpumask.cbcpu);
        destroy_workqueue(pinst->serial_wq);
        destroy_workqueue(pinst->parallel_wq);
        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,
};
ATTRIBUTE_GROUPS(padata_default);

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 const struct kobj_type padata_attr_type = {
        .sysfs_ops = &padata_sysfs_ops,
        .default_groups = padata_default_groups,
        .release = padata_sysfs_release,
};

/**
 * padata_alloc - allocate and initialize a padata instance
 * @name: used to identify the instance
 *
 * Return: new instance on success, NULL on error
 */
struct padata_instance *padata_alloc(const char *name)
{
        struct padata_instance *pinst;

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

        pinst->parallel_wq = alloc_workqueue("%s_parallel", WQ_UNBOUND, 0,
                                             name);
        if (!pinst->parallel_wq)
                goto err_free_inst;

        cpus_read_lock();

        pinst->serial_wq = alloc_workqueue("%s_serial", WQ_MEM_RECLAIM |
                                           WQ_CPU_INTENSIVE, 1, name);
        if (!pinst->serial_wq)
                goto err_put_cpus;

        if (!alloc_cpumask_var(&pinst->cpumask.pcpu, GFP_KERNEL))
                goto err_free_serial_wq;
        if (!alloc_cpumask_var(&pinst->cpumask.cbcpu, GFP_KERNEL)) {
                free_cpumask_var(pinst->cpumask.pcpu);
                goto err_free_serial_wq;
        }

        INIT_LIST_HEAD(&pinst->pslist);

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

        if (padata_setup_cpumasks(pinst))
                goto err_free_masks;

        __padata_start(pinst);

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

#ifdef CONFIG_HOTPLUG_CPU
        cpuhp_state_add_instance_nocalls_cpuslocked(hp_online,
                                                    &pinst->cpu_online_node);
        cpuhp_state_add_instance_nocalls_cpuslocked(CPUHP_PADATA_DEAD,
                                                    &pinst->cpu_dead_node);
#endif

        cpus_read_unlock();

        return pinst;

err_free_masks:
        free_cpumask_var(pinst->cpumask.pcpu);
        free_cpumask_var(pinst->cpumask.cbcpu);
err_free_serial_wq:
        destroy_workqueue(pinst->serial_wq);
err_put_cpus:
        cpus_read_unlock();
        destroy_workqueue(pinst->parallel_wq);
err_free_inst:
        kfree(pinst);
err:
        return NULL;
}
EXPORT_SYMBOL(padata_alloc);

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

/**
 * padata_alloc_shell - Allocate and initialize padata shell.
 *
 * @pinst: Parent padata_instance object.
 *
 * Return: new shell on success, NULL on error
 */
struct padata_shell *padata_alloc_shell(struct padata_instance *pinst)
{
        struct parallel_data *pd;
        struct padata_shell *ps;

        ps = kzalloc(sizeof(*ps), GFP_KERNEL);
        if (!ps)
                goto out;

        ps->pinst = pinst;

        cpus_read_lock();
        pd = padata_alloc_pd(ps);
        cpus_read_unlock();

        if (!pd)
                goto out_free_ps;

        mutex_lock(&pinst->lock);
        RCU_INIT_POINTER(ps->pd, pd);
        list_add(&ps->list, &pinst->pslist);
        mutex_unlock(&pinst->lock);

        return ps;

out_free_ps:
        kfree(ps);
out:
        return NULL;
}
EXPORT_SYMBOL(padata_alloc_shell);

/**
 * padata_free_shell - free a padata shell
 *
 * @ps: padata shell to free
 */
void padata_free_shell(struct padata_shell *ps)
{
        struct parallel_data *pd;

        if (!ps)
                return;

        mutex_lock(&ps->pinst->lock);
        list_del(&ps->list);
        pd = rcu_dereference_protected(ps->pd, 1);
        if (refcount_dec_and_test(&pd->refcnt))
                padata_free_pd(pd);
        mutex_unlock(&ps->pinst->lock);

        kfree(ps);
}
EXPORT_SYMBOL(padata_free_shell);

void __init padata_init(void)
{
        unsigned int i, possible_cpus;
#ifdef CONFIG_HOTPLUG_CPU
        int ret;

        ret = cpuhp_setup_state_multi(CPUHP_AP_ONLINE_DYN, "padata:online",
                                      padata_cpu_online, NULL);
        if (ret < 0)
                goto err;
        hp_online = ret;

        ret = cpuhp_setup_state_multi(CPUHP_PADATA_DEAD, "padata:dead",
                                      NULL, padata_cpu_dead);
        if (ret < 0)
                goto remove_online_state;
#endif

        possible_cpus = num_possible_cpus();
        padata_works = kmalloc_array(possible_cpus, sizeof(struct padata_work),
                                     GFP_KERNEL);
        if (!padata_works)
                goto remove_dead_state;

        for (i = 0; i < possible_cpus; ++i)
                list_add(&padata_works[i].pw_list, &padata_free_works);

        return;

remove_dead_state:
#ifdef CONFIG_HOTPLUG_CPU
        cpuhp_remove_multi_state(CPUHP_PADATA_DEAD);
remove_online_state:
        cpuhp_remove_multi_state(hp_online);
err:
#endif
        pr_warn("padata: initialization failed\n");
}