padata: Generic parallelization/serialization interface

This patch introduces an interface to process data objects
in parallel. The parallelized objects return after serialization
in the same order as they were before the parallelization.

Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

4 files changed, 783 insertions, 0 deletions

diff --git a/include/linux/padata.h b/include/linux/padata.h
new file mode 100644
index 000000000000..51611da9c498
--- /dev/null
+++ b/include/linux/padata.h
@@ -0,0 +1,88 @@
+/*
+ * padata.h - header for the padata parallelization interface
+ *
+ * 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.
+ */
+
+#ifndef PADATA_H
+#define PADATA_H
+
+#include <linux/workqueue.h>
+#include <linux/spinlock.h>
+#include <linux/list.h>
+
+struct padata_priv {
+        struct list_head        list;
+        struct parallel_data    *pd;
+        int                     cb_cpu;
+        int                     seq_nr;
+        int                     info;
+        void                    (*parallel)(struct padata_priv *padata);
+        void                    (*serial)(struct padata_priv *padata);
+};
+
+struct padata_list {
+        struct list_head        list;
+        spinlock_t              lock;
+};
+
+struct padata_queue {
+        struct padata_list      parallel;
+        struct padata_list      reorder;
+        struct padata_list      serial;
+        struct work_struct      pwork;
+        struct work_struct      swork;
+        struct parallel_data    *pd;
+        atomic_t                num_obj;
+        int                     cpu_index;
+};
+
+struct parallel_data {
+        struct padata_instance  *pinst;
+        struct padata_queue     *queue;
+        atomic_t                seq_nr;
+        atomic_t                reorder_objects;
+        atomic_t                refcnt;
+        unsigned int            max_seq_nr;
+        cpumask_var_t           cpumask;
+        spinlock_t              lock;
+};
+
+struct padata_instance {
+        struct notifier_block   cpu_notifier;
+        struct workqueue_struct *wq;
+        struct parallel_data    *pd;
+        cpumask_var_t           cpumask;
+        struct mutex            lock;
+        u8                      flags;
+#define PADATA_INIT             1
+#define PADATA_RESET            2
+};
+
+extern struct padata_instance *padata_alloc(const struct cpumask *cpumask,
+                                            struct workqueue_struct *wq);
+extern void padata_free(struct padata_instance *pinst);
+extern int padata_do_parallel(struct padata_instance *pinst,
+                              struct padata_priv *padata, int cb_cpu);
+extern void padata_do_serial(struct padata_priv *padata);
+extern int padata_set_cpumask(struct padata_instance *pinst,
+                              cpumask_var_t cpumask);
+extern int padata_add_cpu(struct padata_instance *pinst, int cpu);
+extern int padata_remove_cpu(struct padata_instance *pinst, int cpu);
+extern void padata_start(struct padata_instance *pinst);
+extern void padata_stop(struct padata_instance *pinst);
+#endif
diff --git a/init/Kconfig b/init/Kconfig
index a23da9f01803..9fd23bcc1709 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1252,4 +1252,8 @@ source "block/Kconfig"
 config PREEMPT_NOTIFIERS
         bool
 
+config PADATA
+        depends on SMP
+        bool
+
 source "kernel/Kconfig.locks"
diff --git a/kernel/Makefile b/kernel/Makefile
index 864ff75d65f2..6aebdeb2aa34 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -100,6 +100,7 @@ obj-$(CONFIG_SLOW_WORK_DEBUG) += slow-work-debugfs.o
 obj-$(CONFIG_PERF_EVENTS) += perf_event.o
 obj-$(CONFIG_HAVE_HW_BREAKPOINT) += hw_breakpoint.o
 obj-$(CONFIG_USER_RETURN_NOTIFIER) += user-return-notifier.o
+obj-$(CONFIG_PADATA) += padata.o
 
 ifneq ($(CONFIG_SCHED_OMIT_FRAME_POINTER),y)
 # According to Alan Modra <alan@linuxcare.com.au>, the -fno-omit-frame-pointer is
diff --git a/kernel/padata.c b/kernel/padata.c
new file mode 100644
index 000000000000..6f9bcb8313d6
--- /dev/null
+++ b/kernel/padata.c
@@ -0,0 +1,690 @@
+/*
+ * padata.c - generic interface to process data streams in parallel
+ *
+ * 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/module.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/rcupdate.h>
+
+#define MAX_SEQ_NR INT_MAX - NR_CPUS
+#define MAX_OBJ_NUM 10000 * NR_CPUS
+
+static int padata_index_to_cpu(struct parallel_data *pd, int cpu_index)
+{
+        int cpu, target_cpu;
+
+        target_cpu = cpumask_first(pd->cpumask);
+        for (cpu = 0; cpu < cpu_index; cpu++)
+                target_cpu = cpumask_next(target_cpu, pd->cpumask);
+
+        return target_cpu;
+}
+
+static int padata_cpu_hash(struct padata_priv *padata)
+{
+        int cpu_index;
+        struct parallel_data *pd;
+
+        pd =  padata->pd;
+
+        /*
+         * Hash the sequence numbers to the cpus by taking
+         * seq_nr mod. number of cpus in use.
+         */
+        cpu_index =  padata->seq_nr % cpumask_weight(pd->cpumask);
+
+        return padata_index_to_cpu(pd, cpu_index);
+}
+
+static void padata_parallel_worker(struct work_struct *work)
+{
+        struct padata_queue *queue;
+        struct parallel_data *pd;
+        struct padata_instance *pinst;
+        LIST_HEAD(local_list);
+
+        local_bh_disable();
+        queue = container_of(work, struct padata_queue, pwork);
+        pd = queue->pd;
+        pinst = pd->pinst;
+
+        spin_lock(&queue->parallel.lock);
+        list_replace_init(&queue->parallel.list, &local_list);
+        spin_unlock(&queue->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 cpumask of padata.
+ *
+ * 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_queue *queue;
+        struct parallel_data *pd;
+
+        rcu_read_lock_bh();
+
+        pd = rcu_dereference(pinst->pd);
+
+        err = 0;
+        if (!(pinst->flags & PADATA_INIT))
+                goto out;
+
+        err =  -EBUSY;
+        if ((pinst->flags & PADATA_RESET))
+                goto out;
+
+        if (atomic_read(&pd->refcnt) >= MAX_OBJ_NUM)
+                goto out;
+
+        err = -EINVAL;
+        if (!cpumask_test_cpu(cb_cpu, pd->cpumask))
+                goto out;
+
+        err = -EINPROGRESS;
+        atomic_inc(&pd->refcnt);
+        padata->pd = pd;
+        padata->cb_cpu = cb_cpu;
+
+        if (unlikely(atomic_read(&pd->seq_nr) == pd->max_seq_nr))
+                atomic_set(&pd->seq_nr, -1);
+
+        padata->seq_nr = atomic_inc_return(&pd->seq_nr);
+
+        target_cpu = padata_cpu_hash(padata);
+        queue = per_cpu_ptr(pd->queue, 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->pwork);
+
+out:
+        rcu_read_unlock_bh();
+
+        return err;
+}
+EXPORT_SYMBOL(padata_do_parallel);
+
+static struct padata_priv *padata_get_next(struct parallel_data *pd)
+{
+        int cpu, num_cpus, empty, calc_seq_nr;
+        int seq_nr, next_nr, overrun, next_overrun;
+        struct padata_queue *queue, *next_queue;
+        struct padata_priv *padata;
+        struct padata_list *reorder;
+
+        empty = 0;
+        next_nr = -1;
+        next_overrun = 0;
+        next_queue = NULL;
+
+        num_cpus = cpumask_weight(pd->cpumask);
+
+        for_each_cpu(cpu, pd->cpumask) {
+                queue = per_cpu_ptr(pd->queue, cpu);
+                reorder = &queue->reorder;
+
+                /*
+                 * Calculate the seq_nr of the object that should be
+                 * next in this queue.
+                 */
+                overrun = 0;
+                calc_seq_nr = (atomic_read(&queue->num_obj) * num_cpus)
+                               + queue->cpu_index;
+
+                if (unlikely(calc_seq_nr > pd->max_seq_nr)) {
+                        calc_seq_nr = calc_seq_nr - pd->max_seq_nr - 1;
+                        overrun = 1;
+                }
+
+                if (!list_empty(&reorder->list)) {
+                        padata = list_entry(reorder->list.next,
+                                            struct padata_priv, list);
+
+                        seq_nr  = padata->seq_nr;
+                        BUG_ON(calc_seq_nr != seq_nr);
+                } else {
+                        seq_nr = calc_seq_nr;
+                        empty++;
+                }
+
+                if (next_nr < 0 || seq_nr < next_nr
+                    || (next_overrun && !overrun)) {
+                        next_nr = seq_nr;
+                        next_overrun = overrun;
+                        next_queue = queue;
+                }
+        }
+
+        padata = NULL;
+
+        if (empty == num_cpus)
+                goto out;
+
+        reorder = &next_queue->reorder;
+
+        if (!list_empty(&reorder->list)) {
+                padata = list_entry(reorder->list.next,
+                                    struct padata_priv, list);
+
+                if (unlikely(next_overrun)) {
+                        for_each_cpu(cpu, pd->cpumask) {
+                                queue = per_cpu_ptr(pd->queue, cpu);
+                                atomic_set(&queue->num_obj, 0);
+                        }
+                }
+
+                spin_lock(&reorder->lock);
+                list_del_init(&padata->list);
+                atomic_dec(&pd->reorder_objects);
+                spin_unlock(&reorder->lock);
+
+                atomic_inc(&next_queue->num_obj);
+
+                goto out;
+        }
+
+        if (next_nr % num_cpus == 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)
+{
+        struct padata_priv *padata;
+        struct padata_queue *queue;
+        struct padata_instance *pinst = pd->pinst;
+
+try_again:
+        if (!spin_trylock_bh(&pd->lock))
+                goto out;
+
+        while (1) {
+                padata = padata_get_next(pd);
+
+                if (!padata || PTR_ERR(padata) == -EINPROGRESS)
+                        break;
+
+                if (PTR_ERR(padata) == -ENODATA) {
+                        spin_unlock_bh(&pd->lock);
+                        goto out;
+                }
+
+                queue = per_cpu_ptr(pd->queue, padata->cb_cpu);
+
+                spin_lock(&queue->serial.lock);
+                list_add_tail(&padata->list, &queue->serial.list);
+                spin_unlock(&queue->serial.lock);
+
+                queue_work_on(padata->cb_cpu, pinst->wq, &queue->swork);
+        }
+
+        spin_unlock_bh(&pd->lock);
+
+        if (atomic_read(&pd->reorder_objects))
+                goto try_again;
+
+out:
+        return;
+}
+
+static void padata_serial_worker(struct work_struct *work)
+{
+        struct padata_queue *queue;
+        struct parallel_data *pd;
+        LIST_HEAD(local_list);
+
+        local_bh_disable();
+        queue = container_of(work, struct padata_queue, swork);
+        pd = queue->pd;
+
+        spin_lock(&queue->serial.lock);
+        list_replace_init(&queue->serial.list, &local_list);
+        spin_unlock(&queue->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_queue *queue;
+        struct parallel_data *pd;
+
+        pd = padata->pd;
+
+        cpu = get_cpu();
+        queue = per_cpu_ptr(pd->queue, cpu);
+
+        spin_lock(&queue->reorder.lock);
+        atomic_inc(&pd->reorder_objects);
+        list_add_tail(&padata->list, &queue->reorder.list);
+        spin_unlock(&queue->reorder.lock);
+
+        put_cpu();
+
+        padata_reorder(pd);
+}
+EXPORT_SYMBOL(padata_do_serial);
+
+static struct parallel_data *padata_alloc_pd(struct padata_instance *pinst,
+                                             const struct cpumask *cpumask)
+{
+        int cpu, cpu_index, num_cpus;
+        struct padata_queue *queue;
+        struct parallel_data *pd;
+
+        cpu_index = 0;
+
+        pd = kzalloc(sizeof(struct parallel_data), GFP_KERNEL);
+        if (!pd)
+                goto err;
+
+        pd->queue = alloc_percpu(struct padata_queue);
+        if (!pd->queue)
+                goto err_free_pd;
+
+        if (!alloc_cpumask_var(&pd->cpumask, GFP_KERNEL))
+                goto err_free_queue;
+
+        for_each_possible_cpu(cpu) {
+                queue = per_cpu_ptr(pd->queue, cpu);
+
+                queue->pd = pd;
+
+                if (cpumask_test_cpu(cpu, cpumask)
+                    && cpumask_test_cpu(cpu, cpu_active_mask)) {
+                        queue->cpu_index = cpu_index;
+                        cpu_index++;
+                } else
+                        queue->cpu_index = -1;
+
+                INIT_LIST_HEAD(&queue->reorder.list);
+                INIT_LIST_HEAD(&queue->parallel.list);
+                INIT_LIST_HEAD(&queue->serial.list);
+                spin_lock_init(&queue->reorder.lock);
+                spin_lock_init(&queue->parallel.lock);
+                spin_lock_init(&queue->serial.lock);
+
+                INIT_WORK(&queue->pwork, padata_parallel_worker);
+                INIT_WORK(&queue->swork, padata_serial_worker);
+                atomic_set(&queue->num_obj, 0);
+        }
+
+        cpumask_and(pd->cpumask, cpumask, cpu_active_mask);
+
+        num_cpus = cpumask_weight(pd->cpumask);
+        pd->max_seq_nr = (MAX_SEQ_NR / num_cpus) * num_cpus - 1;
+
+        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_queue:
+        free_percpu(pd->queue);
+err_free_pd:
+        kfree(pd);
+err:
+        return NULL;
+}
+
+static void padata_free_pd(struct parallel_data *pd)
+{
+        free_cpumask_var(pd->cpumask);
+        free_percpu(pd->queue);
+        kfree(pd);
+}
+
+static void padata_replace(struct padata_instance *pinst,
+                           struct parallel_data *pd_new)
+{
+        struct parallel_data *pd_old = pinst->pd;
+
+        pinst->flags |= PADATA_RESET;
+
+        rcu_assign_pointer(pinst->pd, pd_new);
+
+        synchronize_rcu();
+
+        while (atomic_read(&pd_old->refcnt) != 0)
+                yield();
+
+        flush_workqueue(pinst->wq);
+
+        padata_free_pd(pd_old);
+
+        pinst->flags &= ~PADATA_RESET;
+}
+
+/*
+ * padata_set_cpumask - set the cpumask that padata should use
+ *
+ * @pinst: padata instance
+ * @cpumask: the cpumask to use
+ */
+int padata_set_cpumask(struct padata_instance *pinst,
+                        cpumask_var_t cpumask)
+{
+        struct parallel_data *pd;
+        int err = 0;
+
+        might_sleep();
+
+        mutex_lock(&pinst->lock);
+
+        pd = padata_alloc_pd(pinst, cpumask);
+        if (!pd) {
+                err = -ENOMEM;
+                goto out;
+        }
+
+        cpumask_copy(pinst->cpumask, cpumask);
+
+        padata_replace(pinst, pd);
+
+out:
+        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_active_mask)) {
+                pd = padata_alloc_pd(pinst, pinst->cpumask);
+                if (!pd)
+                        return -ENOMEM;
+
+                padata_replace(pinst, pd);
+        }
+
+        return 0;
+}
+
+/*
+ * padata_add_cpu - add a cpu to the padata cpumask
+ *
+ * @pinst: padata instance
+ * @cpu: cpu to add
+ */
+int padata_add_cpu(struct padata_instance *pinst, int cpu)
+{
+        int err;
+
+        might_sleep();
+
+        mutex_lock(&pinst->lock);
+
+        cpumask_set_cpu(cpu, pinst->cpumask);
+        err = __padata_add_cpu(pinst, cpu);
+
+        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;
+
+        if (cpumask_test_cpu(cpu, cpu_online_mask)) {
+                pd = padata_alloc_pd(pinst, pinst->cpumask);
+                if (!pd)
+                        return -ENOMEM;
+
+                padata_replace(pinst, pd);
+        }
+
+        return 0;
+}
+
+/*
+ * padata_remove_cpu - remove a cpu from the padata cpumask
+ *
+ * @pinst: padata instance
+ * @cpu: cpu to remove
+ */
+int padata_remove_cpu(struct padata_instance *pinst, int cpu)
+{
+        int err;
+
+        might_sleep();
+
+        mutex_lock(&pinst->lock);
+
+        cpumask_clear_cpu(cpu, pinst->cpumask);
+        err = __padata_remove_cpu(pinst, cpu);
+
+        mutex_unlock(&pinst->lock);
+
+        return err;
+}
+EXPORT_SYMBOL(padata_remove_cpu);
+
+/*
+ * padata_start - start the parallel processing
+ *
+ * @pinst: padata instance to start
+ */
+void padata_start(struct padata_instance *pinst)
+{
+        might_sleep();
+
+        mutex_lock(&pinst->lock);
+        pinst->flags |= PADATA_INIT;
+        mutex_unlock(&pinst->lock);
+}
+EXPORT_SYMBOL(padata_start);
+
+/*
+ * padata_stop - stop the parallel processing
+ *
+ * @pinst: padata instance to stop
+ */
+void padata_stop(struct padata_instance *pinst)
+{
+        might_sleep();
+
+        mutex_lock(&pinst->lock);
+        pinst->flags &= ~PADATA_INIT;
+        mutex_unlock(&pinst->lock);
+}
+EXPORT_SYMBOL(padata_stop);
+
+static int __cpuinit 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 (!cpumask_test_cpu(cpu, pinst->cpumask))
+                        break;
+                mutex_lock(&pinst->lock);
+                err = __padata_add_cpu(pinst, cpu);
+                mutex_unlock(&pinst->lock);
+                if (err)
+                        return NOTIFY_BAD;
+                break;
+
+        case CPU_DOWN_PREPARE:
+        case CPU_DOWN_PREPARE_FROZEN:
+                if (!cpumask_test_cpu(cpu, pinst->cpumask))
+                        break;
+                mutex_lock(&pinst->lock);
+                err = __padata_remove_cpu(pinst, cpu);
+                mutex_unlock(&pinst->lock);
+                if (err)
+                        return NOTIFY_BAD;
+                break;
+
+        case CPU_UP_CANCELED:
+        case CPU_UP_CANCELED_FROZEN:
+                if (!cpumask_test_cpu(cpu, pinst->cpumask))
+                        break;
+                mutex_lock(&pinst->lock);
+                __padata_remove_cpu(pinst, cpu);
+                mutex_unlock(&pinst->lock);
+
+        case CPU_DOWN_FAILED:
+        case CPU_DOWN_FAILED_FROZEN:
+                if (!cpumask_test_cpu(cpu, pinst->cpumask))
+                        break;
+                mutex_lock(&pinst->lock);
+                __padata_add_cpu(pinst, cpu);
+                mutex_unlock(&pinst->lock);
+        }
+
+        return NOTIFY_OK;
+}
+
+/*
+ * padata_alloc - allocate and initialize a padata instance
+ *
+ * @cpumask: cpumask that padata uses for parallelization
+ * @wq: workqueue to use for the allocated padata instance
+ */
+struct padata_instance *padata_alloc(const struct cpumask *cpumask,
+                                     struct workqueue_struct *wq)
+{
+        int err;
+        struct padata_instance *pinst;
+        struct parallel_data *pd;
+
+        pinst = kzalloc(sizeof(struct padata_instance), GFP_KERNEL);
+        if (!pinst)
+                goto err;
+
+        pd = padata_alloc_pd(pinst, cpumask);
+        if (!pd)
+                goto err_free_inst;
+
+        rcu_assign_pointer(pinst->pd, pd);
+
+        pinst->wq = wq;
+
+        cpumask_copy(pinst->cpumask, cpumask);
+
+        pinst->flags = 0;
+
+        pinst->cpu_notifier.notifier_call = padata_cpu_callback;
+        pinst->cpu_notifier.priority = 0;
+        err = register_hotcpu_notifier(&pinst->cpu_notifier);
+        if (err)
+                goto err_free_pd;
+
+        mutex_init(&pinst->lock);
+
+        return pinst;
+
+err_free_pd:
+        padata_free_pd(pd);
+err_free_inst:
+        kfree(pinst);
+err:
+        return NULL;
+}
+EXPORT_SYMBOL(padata_alloc);
+
+/*
+ * padata_free - free a padata instance
+ *
+ * @ padata_inst: padata instance to free
+ */
+void padata_free(struct padata_instance *pinst)
+{
+        padata_stop(pinst);
+
+        synchronize_rcu();
+
+        while (atomic_read(&pinst->pd->refcnt) != 0)
+                yield();
+
+        unregister_hotcpu_notifier(&pinst->cpu_notifier);
+        padata_free_pd(pinst->pd);
+        kfree(pinst);
+}
+EXPORT_SYMBOL(padata_free);