Linux 4.11-rc6

[linux/fpc-iii.git] / net / sunrpc / sched.c

/*
 * linux/net/sunrpc/sched.c
 *
 * Scheduling for synchronous and asynchronous RPC requests.
 *
 * Copyright (C) 1996 Olaf Kirch, <okir@monad.swb.de>
 *
 * TCP NFS related read + write fixes
 * (C) 1999 Dave Airlie, University of Limerick, Ireland <airlied@linux.ie>
 */

#include <linux/module.h>

#include <linux/sched.h>
#include <linux/interrupt.h>
#include <linux/slab.h>
#include <linux/mempool.h>
#include <linux/smp.h>
#include <linux/spinlock.h>
#include <linux/mutex.h>
#include <linux/freezer.h>

#include <linux/sunrpc/clnt.h>

#include "sunrpc.h"

#if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
#define RPCDBG_FACILITY         RPCDBG_SCHED
#endif

#define CREATE_TRACE_POINTS
#include <trace/events/sunrpc.h>

/*
 * RPC slabs and memory pools
 */
#define RPC_BUFFER_MAXSIZE      (2048)
#define RPC_BUFFER_POOLSIZE     (8)
#define RPC_TASK_POOLSIZE       (8)
static struct kmem_cache        *rpc_task_slabp __read_mostly;
static struct kmem_cache        *rpc_buffer_slabp __read_mostly;
static mempool_t        *rpc_task_mempool __read_mostly;
static mempool_t        *rpc_buffer_mempool __read_mostly;

static void                     rpc_async_schedule(struct work_struct *);
static void                      rpc_release_task(struct rpc_task *task);
static void __rpc_queue_timer_fn(unsigned long ptr);

/*
 * RPC tasks sit here while waiting for conditions to improve.
 */
static struct rpc_wait_queue delay_queue;

/*
 * rpciod-related stuff
 */
struct workqueue_struct *rpciod_workqueue __read_mostly;
struct workqueue_struct *xprtiod_workqueue __read_mostly;

/*
 * Disable the timer for a given RPC task. Should be called with
 * queue->lock and bh_disabled in order to avoid races within
 * rpc_run_timer().
 */
static void
__rpc_disable_timer(struct rpc_wait_queue *queue, struct rpc_task *task)
{
        if (task->tk_timeout == 0)
                return;
        dprintk("RPC: %5u disabling timer\n", task->tk_pid);
        task->tk_timeout = 0;
        list_del(&task->u.tk_wait.timer_list);
        if (list_empty(&queue->timer_list.list))
                del_timer(&queue->timer_list.timer);
}

static void
rpc_set_queue_timer(struct rpc_wait_queue *queue, unsigned long expires)
{
        queue->timer_list.expires = expires;
        mod_timer(&queue->timer_list.timer, expires);
}

/*
 * Set up a timer for the current task.
 */
static void
__rpc_add_timer(struct rpc_wait_queue *queue, struct rpc_task *task)
{
        if (!task->tk_timeout)
                return;

        dprintk("RPC: %5u setting alarm for %u ms\n",
                task->tk_pid, jiffies_to_msecs(task->tk_timeout));

        task->u.tk_wait.expires = jiffies + task->tk_timeout;
        if (list_empty(&queue->timer_list.list) || time_before(task->u.tk_wait.expires, queue->timer_list.expires))
                rpc_set_queue_timer(queue, task->u.tk_wait.expires);
        list_add(&task->u.tk_wait.timer_list, &queue->timer_list.list);
}

static void rpc_rotate_queue_owner(struct rpc_wait_queue *queue)
{
        struct list_head *q = &queue->tasks[queue->priority];
        struct rpc_task *task;

        if (!list_empty(q)) {
                task = list_first_entry(q, struct rpc_task, u.tk_wait.list);
                if (task->tk_owner == queue->owner)
                        list_move_tail(&task->u.tk_wait.list, q);
        }
}

static void rpc_set_waitqueue_priority(struct rpc_wait_queue *queue, int priority)
{
        if (queue->priority != priority) {
                /* Fairness: rotate the list when changing priority */
                rpc_rotate_queue_owner(queue);
                queue->priority = priority;
        }
}

static void rpc_set_waitqueue_owner(struct rpc_wait_queue *queue, pid_t pid)
{
        queue->owner = pid;
        queue->nr = RPC_BATCH_COUNT;
}

static void rpc_reset_waitqueue_priority(struct rpc_wait_queue *queue)
{
        rpc_set_waitqueue_priority(queue, queue->maxpriority);
        rpc_set_waitqueue_owner(queue, 0);
}

/*
 * Add new request to a priority queue.
 */
static void __rpc_add_wait_queue_priority(struct rpc_wait_queue *queue,
                struct rpc_task *task,
                unsigned char queue_priority)
{
        struct list_head *q;
        struct rpc_task *t;

        INIT_LIST_HEAD(&task->u.tk_wait.links);
        if (unlikely(queue_priority > queue->maxpriority))
                queue_priority = queue->maxpriority;
        if (queue_priority > queue->priority)
                rpc_set_waitqueue_priority(queue, queue_priority);
        q = &queue->tasks[queue_priority];
        list_for_each_entry(t, q, u.tk_wait.list) {
                if (t->tk_owner == task->tk_owner) {
                        list_add_tail(&task->u.tk_wait.list, &t->u.tk_wait.links);
                        return;
                }
        }
        list_add_tail(&task->u.tk_wait.list, q);
}

/*
 * Add new request to wait queue.
 *
 * Swapper tasks always get inserted at the head of the queue.
 * This should avoid many nasty memory deadlocks and hopefully
 * improve overall performance.
 * Everyone else gets appended to the queue to ensure proper FIFO behavior.
 */
static void __rpc_add_wait_queue(struct rpc_wait_queue *queue,
                struct rpc_task *task,
                unsigned char queue_priority)
{
        WARN_ON_ONCE(RPC_IS_QUEUED(task));
        if (RPC_IS_QUEUED(task))
                return;

        if (RPC_IS_PRIORITY(queue))
                __rpc_add_wait_queue_priority(queue, task, queue_priority);
        else if (RPC_IS_SWAPPER(task))
                list_add(&task->u.tk_wait.list, &queue->tasks[0]);
        else
                list_add_tail(&task->u.tk_wait.list, &queue->tasks[0]);
        task->tk_waitqueue = queue;
        queue->qlen++;
        /* barrier matches the read in rpc_wake_up_task_queue_locked() */
        smp_wmb();
        rpc_set_queued(task);

        dprintk("RPC: %5u added to queue %p \"%s\"\n",
                        task->tk_pid, queue, rpc_qname(queue));
}

/*
 * Remove request from a priority queue.
 */
static void __rpc_remove_wait_queue_priority(struct rpc_task *task)
{
        struct rpc_task *t;

        if (!list_empty(&task->u.tk_wait.links)) {
                t = list_entry(task->u.tk_wait.links.next, struct rpc_task, u.tk_wait.list);
                list_move(&t->u.tk_wait.list, &task->u.tk_wait.list);
                list_splice_init(&task->u.tk_wait.links, &t->u.tk_wait.links);
        }
}

/*
 * Remove request from queue.
 * Note: must be called with spin lock held.
 */
static void __rpc_remove_wait_queue(struct rpc_wait_queue *queue, struct rpc_task *task)
{
        __rpc_disable_timer(queue, task);
        if (RPC_IS_PRIORITY(queue))
                __rpc_remove_wait_queue_priority(task);
        list_del(&task->u.tk_wait.list);
        queue->qlen--;
        dprintk("RPC: %5u removed from queue %p \"%s\"\n",
                        task->tk_pid, queue, rpc_qname(queue));
}

static void __rpc_init_priority_wait_queue(struct rpc_wait_queue *queue, const char *qname, unsigned char nr_queues)
{
        int i;

        spin_lock_init(&queue->lock);
        for (i = 0; i < ARRAY_SIZE(queue->tasks); i++)
                INIT_LIST_HEAD(&queue->tasks[i]);
        queue->maxpriority = nr_queues - 1;
        rpc_reset_waitqueue_priority(queue);
        queue->qlen = 0;
        setup_timer(&queue->timer_list.timer, __rpc_queue_timer_fn, (unsigned long)queue);
        INIT_LIST_HEAD(&queue->timer_list.list);
        rpc_assign_waitqueue_name(queue, qname);
}

void rpc_init_priority_wait_queue(struct rpc_wait_queue *queue, const char *qname)
{
        __rpc_init_priority_wait_queue(queue, qname, RPC_NR_PRIORITY);
}
EXPORT_SYMBOL_GPL(rpc_init_priority_wait_queue);

void rpc_init_wait_queue(struct rpc_wait_queue *queue, const char *qname)
{
        __rpc_init_priority_wait_queue(queue, qname, 1);
}
EXPORT_SYMBOL_GPL(rpc_init_wait_queue);

void rpc_destroy_wait_queue(struct rpc_wait_queue *queue)
{
        del_timer_sync(&queue->timer_list.timer);
}
EXPORT_SYMBOL_GPL(rpc_destroy_wait_queue);

static int rpc_wait_bit_killable(struct wait_bit_key *key, int mode)
{
        freezable_schedule_unsafe();
        if (signal_pending_state(mode, current))
                return -ERESTARTSYS;
        return 0;
}

#if IS_ENABLED(CONFIG_SUNRPC_DEBUG) || IS_ENABLED(CONFIG_TRACEPOINTS)
static void rpc_task_set_debuginfo(struct rpc_task *task)
{
        static atomic_t rpc_pid;

        task->tk_pid = atomic_inc_return(&rpc_pid);
}
#else
static inline void rpc_task_set_debuginfo(struct rpc_task *task)
{
}
#endif

static void rpc_set_active(struct rpc_task *task)
{
        trace_rpc_task_begin(task->tk_client, task, NULL);

        rpc_task_set_debuginfo(task);
        set_bit(RPC_TASK_ACTIVE, &task->tk_runstate);
}

/*
 * Mark an RPC call as having completed by clearing the 'active' bit
 * and then waking up all tasks that were sleeping.
 */
static int rpc_complete_task(struct rpc_task *task)
{
        void *m = &task->tk_runstate;
        wait_queue_head_t *wq = bit_waitqueue(m, RPC_TASK_ACTIVE);
        struct wait_bit_key k = __WAIT_BIT_KEY_INITIALIZER(m, RPC_TASK_ACTIVE);
        unsigned long flags;
        int ret;

        trace_rpc_task_complete(task->tk_client, task, NULL);

        spin_lock_irqsave(&wq->lock, flags);
        clear_bit(RPC_TASK_ACTIVE, &task->tk_runstate);
        ret = atomic_dec_and_test(&task->tk_count);
        if (waitqueue_active(wq))
                __wake_up_locked_key(wq, TASK_NORMAL, &k);
        spin_unlock_irqrestore(&wq->lock, flags);
        return ret;
}

/*
 * Allow callers to wait for completion of an RPC call
 *
 * Note the use of out_of_line_wait_on_bit() rather than wait_on_bit()
 * to enforce taking of the wq->lock and hence avoid races with
 * rpc_complete_task().
 */
int __rpc_wait_for_completion_task(struct rpc_task *task, wait_bit_action_f *action)
{
        if (action == NULL)
                action = rpc_wait_bit_killable;
        return out_of_line_wait_on_bit(&task->tk_runstate, RPC_TASK_ACTIVE,
                        action, TASK_KILLABLE);
}
EXPORT_SYMBOL_GPL(__rpc_wait_for_completion_task);

/*
 * Make an RPC task runnable.
 *
 * Note: If the task is ASYNC, and is being made runnable after sitting on an
 * rpc_wait_queue, this must be called with the queue spinlock held to protect
 * the wait queue operation.
 * Note the ordering of rpc_test_and_set_running() and rpc_clear_queued(),
 * which is needed to ensure that __rpc_execute() doesn't loop (due to the
 * lockless RPC_IS_QUEUED() test) before we've had a chance to test
 * the RPC_TASK_RUNNING flag.
 */
static void rpc_make_runnable(struct workqueue_struct *wq,
                struct rpc_task *task)
{
        bool need_wakeup = !rpc_test_and_set_running(task);

        rpc_clear_queued(task);
        if (!need_wakeup)
                return;
        if (RPC_IS_ASYNC(task)) {
                INIT_WORK(&task->u.tk_work, rpc_async_schedule);
                queue_work(wq, &task->u.tk_work);
        } else
                wake_up_bit(&task->tk_runstate, RPC_TASK_QUEUED);
}

/*
 * Prepare for sleeping on a wait queue.
 * By always appending tasks to the list we ensure FIFO behavior.
 * NB: An RPC task will only receive interrupt-driven events as long
 * as it's on a wait queue.
 */
static void __rpc_sleep_on_priority(struct rpc_wait_queue *q,
                struct rpc_task *task,
                rpc_action action,
                unsigned char queue_priority)
{
        dprintk("RPC: %5u sleep_on(queue \"%s\" time %lu)\n",
                        task->tk_pid, rpc_qname(q), jiffies);

        trace_rpc_task_sleep(task->tk_client, task, q);

        __rpc_add_wait_queue(q, task, queue_priority);

        WARN_ON_ONCE(task->tk_callback != NULL);
        task->tk_callback = action;
        __rpc_add_timer(q, task);
}

void rpc_sleep_on(struct rpc_wait_queue *q, struct rpc_task *task,
                                rpc_action action)
{
        /* We shouldn't ever put an inactive task to sleep */
        WARN_ON_ONCE(!RPC_IS_ACTIVATED(task));
        if (!RPC_IS_ACTIVATED(task)) {
                task->tk_status = -EIO;
                rpc_put_task_async(task);
                return;
        }

        /*
         * Protect the queue operations.
         */
        spin_lock_bh(&q->lock);
        __rpc_sleep_on_priority(q, task, action, task->tk_priority);
        spin_unlock_bh(&q->lock);
}
EXPORT_SYMBOL_GPL(rpc_sleep_on);

void rpc_sleep_on_priority(struct rpc_wait_queue *q, struct rpc_task *task,
                rpc_action action, int priority)
{
        /* We shouldn't ever put an inactive task to sleep */
        WARN_ON_ONCE(!RPC_IS_ACTIVATED(task));
        if (!RPC_IS_ACTIVATED(task)) {
                task->tk_status = -EIO;
                rpc_put_task_async(task);
                return;
        }

        /*
         * Protect the queue operations.
         */
        spin_lock_bh(&q->lock);
        __rpc_sleep_on_priority(q, task, action, priority - RPC_PRIORITY_LOW);
        spin_unlock_bh(&q->lock);
}
EXPORT_SYMBOL_GPL(rpc_sleep_on_priority);

/**
 * __rpc_do_wake_up_task_on_wq - wake up a single rpc_task
 * @wq: workqueue on which to run task
 * @queue: wait queue
 * @task: task to be woken up
 *
 * Caller must hold queue->lock, and have cleared the task queued flag.
 */
static void __rpc_do_wake_up_task_on_wq(struct workqueue_struct *wq,
                struct rpc_wait_queue *queue,
                struct rpc_task *task)
{
        dprintk("RPC: %5u __rpc_wake_up_task (now %lu)\n",
                        task->tk_pid, jiffies);

        /* Has the task been executed yet? If not, we cannot wake it up! */
        if (!RPC_IS_ACTIVATED(task)) {
                printk(KERN_ERR "RPC: Inactive task (%p) being woken up!\n", task);
                return;
        }

        trace_rpc_task_wakeup(task->tk_client, task, queue);

        __rpc_remove_wait_queue(queue, task);

        rpc_make_runnable(wq, task);

        dprintk("RPC:       __rpc_wake_up_task done\n");
}

/*
 * Wake up a queued task while the queue lock is being held
 */
static void rpc_wake_up_task_on_wq_queue_locked(struct workqueue_struct *wq,
                struct rpc_wait_queue *queue, struct rpc_task *task)
{
        if (RPC_IS_QUEUED(task)) {
                smp_rmb();
                if (task->tk_waitqueue == queue)
                        __rpc_do_wake_up_task_on_wq(wq, queue, task);
        }
}

/*
 * Wake up a queued task while the queue lock is being held
 */
static void rpc_wake_up_task_queue_locked(struct rpc_wait_queue *queue, struct rpc_task *task)
{
        rpc_wake_up_task_on_wq_queue_locked(rpciod_workqueue, queue, task);
}

/*
 * Wake up a task on a specific queue
 */
void rpc_wake_up_queued_task(struct rpc_wait_queue *queue, struct rpc_task *task)
{
        spin_lock_bh(&queue->lock);
        rpc_wake_up_task_queue_locked(queue, task);
        spin_unlock_bh(&queue->lock);
}
EXPORT_SYMBOL_GPL(rpc_wake_up_queued_task);

/*
 * Wake up the next task on a priority queue.
 */
static struct rpc_task *__rpc_find_next_queued_priority(struct rpc_wait_queue *queue)
{
        struct list_head *q;
        struct rpc_task *task;

        /*
         * Service a batch of tasks from a single owner.
         */
        q = &queue->tasks[queue->priority];
        if (!list_empty(q)) {
                task = list_entry(q->next, struct rpc_task, u.tk_wait.list);
                if (queue->owner == task->tk_owner) {
                        if (--queue->nr)
                                goto out;
                        list_move_tail(&task->u.tk_wait.list, q);
                }
                /*
                 * Check if we need to switch queues.
                 */
                goto new_owner;
        }

        /*
         * Service the next queue.
         */
        do {
                if (q == &queue->tasks[0])
                        q = &queue->tasks[queue->maxpriority];
                else
                        q = q - 1;
                if (!list_empty(q)) {
                        task = list_entry(q->next, struct rpc_task, u.tk_wait.list);
                        goto new_queue;
                }
        } while (q != &queue->tasks[queue->priority]);

        rpc_reset_waitqueue_priority(queue);
        return NULL;

new_queue:
        rpc_set_waitqueue_priority(queue, (unsigned int)(q - &queue->tasks[0]));
new_owner:
        rpc_set_waitqueue_owner(queue, task->tk_owner);
out:
        return task;
}

static struct rpc_task *__rpc_find_next_queued(struct rpc_wait_queue *queue)
{
        if (RPC_IS_PRIORITY(queue))
                return __rpc_find_next_queued_priority(queue);
        if (!list_empty(&queue->tasks[0]))
                return list_first_entry(&queue->tasks[0], struct rpc_task, u.tk_wait.list);
        return NULL;
}

/*
 * Wake up the first task on the wait queue.
 */
struct rpc_task *rpc_wake_up_first_on_wq(struct workqueue_struct *wq,
                struct rpc_wait_queue *queue,
                bool (*func)(struct rpc_task *, void *), void *data)
{
        struct rpc_task *task = NULL;

        dprintk("RPC:       wake_up_first(%p \"%s\")\n",
                        queue, rpc_qname(queue));
        spin_lock_bh(&queue->lock);
        task = __rpc_find_next_queued(queue);
        if (task != NULL) {
                if (func(task, data))
                        rpc_wake_up_task_on_wq_queue_locked(wq, queue, task);
                else
                        task = NULL;
        }
        spin_unlock_bh(&queue->lock);

        return task;
}

/*
 * Wake up the first task on the wait queue.
 */
struct rpc_task *rpc_wake_up_first(struct rpc_wait_queue *queue,
                bool (*func)(struct rpc_task *, void *), void *data)
{
        return rpc_wake_up_first_on_wq(rpciod_workqueue, queue, func, data);
}
EXPORT_SYMBOL_GPL(rpc_wake_up_first);

static bool rpc_wake_up_next_func(struct rpc_task *task, void *data)
{
        return true;
}

/*
 * Wake up the next task on the wait queue.
*/
struct rpc_task *rpc_wake_up_next(struct rpc_wait_queue *queue)
{
        return rpc_wake_up_first(queue, rpc_wake_up_next_func, NULL);
}
EXPORT_SYMBOL_GPL(rpc_wake_up_next);

/**
 * rpc_wake_up - wake up all rpc_tasks
 * @queue: rpc_wait_queue on which the tasks are sleeping
 *
 * Grabs queue->lock
 */
void rpc_wake_up(struct rpc_wait_queue *queue)
{
        struct list_head *head;

        spin_lock_bh(&queue->lock);
        head = &queue->tasks[queue->maxpriority];
        for (;;) {
                while (!list_empty(head)) {
                        struct rpc_task *task;
                        task = list_first_entry(head,
                                        struct rpc_task,
                                        u.tk_wait.list);
                        rpc_wake_up_task_queue_locked(queue, task);
                }
                if (head == &queue->tasks[0])
                        break;
                head--;
        }
        spin_unlock_bh(&queue->lock);
}
EXPORT_SYMBOL_GPL(rpc_wake_up);

/**
 * rpc_wake_up_status - wake up all rpc_tasks and set their status value.
 * @queue: rpc_wait_queue on which the tasks are sleeping
 * @status: status value to set
 *
 * Grabs queue->lock
 */
void rpc_wake_up_status(struct rpc_wait_queue *queue, int status)
{
        struct list_head *head;

        spin_lock_bh(&queue->lock);
        head = &queue->tasks[queue->maxpriority];
        for (;;) {
                while (!list_empty(head)) {
                        struct rpc_task *task;
                        task = list_first_entry(head,
                                        struct rpc_task,
                                        u.tk_wait.list);
                        task->tk_status = status;
                        rpc_wake_up_task_queue_locked(queue, task);
                }
                if (head == &queue->tasks[0])
                        break;
                head--;
        }
        spin_unlock_bh(&queue->lock);
}
EXPORT_SYMBOL_GPL(rpc_wake_up_status);

static void __rpc_queue_timer_fn(unsigned long ptr)
{
        struct rpc_wait_queue *queue = (struct rpc_wait_queue *)ptr;
        struct rpc_task *task, *n;
        unsigned long expires, now, timeo;

        spin_lock(&queue->lock);
        expires = now = jiffies;
        list_for_each_entry_safe(task, n, &queue->timer_list.list, u.tk_wait.timer_list) {
                timeo = task->u.tk_wait.expires;
                if (time_after_eq(now, timeo)) {
                        dprintk("RPC: %5u timeout\n", task->tk_pid);
                        task->tk_status = -ETIMEDOUT;
                        rpc_wake_up_task_queue_locked(queue, task);
                        continue;
                }
                if (expires == now || time_after(expires, timeo))
                        expires = timeo;
        }
        if (!list_empty(&queue->timer_list.list))
                rpc_set_queue_timer(queue, expires);
        spin_unlock(&queue->lock);
}

static void __rpc_atrun(struct rpc_task *task)
{
        if (task->tk_status == -ETIMEDOUT)
                task->tk_status = 0;
}

/*
 * Run a task at a later time
 */
void rpc_delay(struct rpc_task *task, unsigned long delay)
{
        task->tk_timeout = delay;
        rpc_sleep_on(&delay_queue, task, __rpc_atrun);
}
EXPORT_SYMBOL_GPL(rpc_delay);

/*
 * Helper to call task->tk_ops->rpc_call_prepare
 */
void rpc_prepare_task(struct rpc_task *task)
{
        task->tk_ops->rpc_call_prepare(task, task->tk_calldata);
}

static void
rpc_init_task_statistics(struct rpc_task *task)
{
        /* Initialize retry counters */
        task->tk_garb_retry = 2;
        task->tk_cred_retry = 2;
        task->tk_rebind_retry = 2;

        /* starting timestamp */
        task->tk_start = ktime_get();
}

static void
rpc_reset_task_statistics(struct rpc_task *task)
{
        task->tk_timeouts = 0;
        task->tk_flags &= ~(RPC_CALL_MAJORSEEN|RPC_TASK_KILLED|RPC_TASK_SENT);

        rpc_init_task_statistics(task);
}

/*
 * Helper that calls task->tk_ops->rpc_call_done if it exists
 */
void rpc_exit_task(struct rpc_task *task)
{
        task->tk_action = NULL;
        if (task->tk_ops->rpc_call_done != NULL) {
                task->tk_ops->rpc_call_done(task, task->tk_calldata);
                if (task->tk_action != NULL) {
                        WARN_ON(RPC_ASSASSINATED(task));
                        /* Always release the RPC slot and buffer memory */
                        xprt_release(task);
                        rpc_reset_task_statistics(task);
                }
        }
}

void rpc_exit(struct rpc_task *task, int status)
{
        task->tk_status = status;
        task->tk_action = rpc_exit_task;
        if (RPC_IS_QUEUED(task))
                rpc_wake_up_queued_task(task->tk_waitqueue, task);
}
EXPORT_SYMBOL_GPL(rpc_exit);

void rpc_release_calldata(const struct rpc_call_ops *ops, void *calldata)
{
        if (ops->rpc_release != NULL)
                ops->rpc_release(calldata);
}

/*
 * This is the RPC `scheduler' (or rather, the finite state machine).
 */
static void __rpc_execute(struct rpc_task *task)
{
        struct rpc_wait_queue *queue;
        int task_is_async = RPC_IS_ASYNC(task);
        int status = 0;

        dprintk("RPC: %5u __rpc_execute flags=0x%x\n",
                        task->tk_pid, task->tk_flags);

        WARN_ON_ONCE(RPC_IS_QUEUED(task));
        if (RPC_IS_QUEUED(task))
                return;

        for (;;) {
                void (*do_action)(struct rpc_task *);

                /*
                 * Execute any pending callback first.
                 */
                do_action = task->tk_callback;
                task->tk_callback = NULL;
                if (do_action == NULL) {
                        /*
                         * Perform the next FSM step.
                         * tk_action may be NULL if the task has been killed.
                         * In particular, note that rpc_killall_tasks may
                         * do this at any time, so beware when dereferencing.
                         */
                        do_action = task->tk_action;
                        if (do_action == NULL)
                                break;
                }
                trace_rpc_task_run_action(task->tk_client, task, task->tk_action);
                do_action(task);

                /*
                 * Lockless check for whether task is sleeping or not.
                 */
                if (!RPC_IS_QUEUED(task))
                        continue;
                /*
                 * The queue->lock protects against races with
                 * rpc_make_runnable().
                 *
                 * Note that once we clear RPC_TASK_RUNNING on an asynchronous
                 * rpc_task, rpc_make_runnable() can assign it to a
                 * different workqueue. We therefore cannot assume that the
                 * rpc_task pointer may still be dereferenced.
                 */
                queue = task->tk_waitqueue;
                spin_lock_bh(&queue->lock);
                if (!RPC_IS_QUEUED(task)) {
                        spin_unlock_bh(&queue->lock);
                        continue;
                }
                rpc_clear_running(task);
                spin_unlock_bh(&queue->lock);
                if (task_is_async)
                        return;

                /* sync task: sleep here */
                dprintk("RPC: %5u sync task going to sleep\n", task->tk_pid);
                status = out_of_line_wait_on_bit(&task->tk_runstate,
                                RPC_TASK_QUEUED, rpc_wait_bit_killable,
                                TASK_KILLABLE);
                if (status == -ERESTARTSYS) {
                        /*
                         * When a sync task receives a signal, it exits with
                         * -ERESTARTSYS. In order to catch any callbacks that
                         * clean up after sleeping on some queue, we don't
                         * break the loop here, but go around once more.
                         */
                        dprintk("RPC: %5u got signal\n", task->tk_pid);
                        task->tk_flags |= RPC_TASK_KILLED;
                        rpc_exit(task, -ERESTARTSYS);
                }
                dprintk("RPC: %5u sync task resuming\n", task->tk_pid);
        }

        dprintk("RPC: %5u return %d, status %d\n", task->tk_pid, status,
                        task->tk_status);
        /* Release all resources associated with the task */
        rpc_release_task(task);
}

/*
 * User-visible entry point to the scheduler.
 *
 * This may be called recursively if e.g. an async NFS task updates
 * the attributes and finds that dirty pages must be flushed.
 * NOTE: Upon exit of this function the task is guaranteed to be
 *       released. In particular note that tk_release() will have
 *       been called, so your task memory may have been freed.
 */
void rpc_execute(struct rpc_task *task)
{
        bool is_async = RPC_IS_ASYNC(task);

        rpc_set_active(task);
        rpc_make_runnable(rpciod_workqueue, task);
        if (!is_async)
                __rpc_execute(task);
}

static void rpc_async_schedule(struct work_struct *work)
{
        __rpc_execute(container_of(work, struct rpc_task, u.tk_work));
}

/**
 * rpc_malloc - allocate RPC buffer resources
 * @task: RPC task
 *
 * A single memory region is allocated, which is split between the
 * RPC call and RPC reply that this task is being used for. When
 * this RPC is retired, the memory is released by calling rpc_free.
 *
 * To prevent rpciod from hanging, this allocator never sleeps,
 * returning -ENOMEM and suppressing warning if the request cannot
 * be serviced immediately. The caller can arrange to sleep in a
 * way that is safe for rpciod.
 *
 * Most requests are 'small' (under 2KiB) and can be serviced from a
 * mempool, ensuring that NFS reads and writes can always proceed,
 * and that there is good locality of reference for these buffers.
 *
 * In order to avoid memory starvation triggering more writebacks of
 * NFS requests, we avoid using GFP_KERNEL.
 */
int rpc_malloc(struct rpc_task *task)
{
        struct rpc_rqst *rqst = task->tk_rqstp;
        size_t size = rqst->rq_callsize + rqst->rq_rcvsize;
        struct rpc_buffer *buf;
        gfp_t gfp = GFP_NOIO | __GFP_NOWARN;

        if (RPC_IS_SWAPPER(task))
                gfp = __GFP_MEMALLOC | GFP_NOWAIT | __GFP_NOWARN;

        size += sizeof(struct rpc_buffer);
        if (size <= RPC_BUFFER_MAXSIZE)
                buf = mempool_alloc(rpc_buffer_mempool, gfp);
        else
                buf = kmalloc(size, gfp);

        if (!buf)
                return -ENOMEM;

        buf->len = size;
        dprintk("RPC: %5u allocated buffer of size %zu at %p\n",
                        task->tk_pid, size, buf);
        rqst->rq_buffer = buf->data;
        rqst->rq_rbuffer = (char *)rqst->rq_buffer + rqst->rq_callsize;
        return 0;
}
EXPORT_SYMBOL_GPL(rpc_malloc);

/**
 * rpc_free - free RPC buffer resources allocated via rpc_malloc
 * @task: RPC task
 *
 */
void rpc_free(struct rpc_task *task)
{
        void *buffer = task->tk_rqstp->rq_buffer;
        size_t size;
        struct rpc_buffer *buf;

        buf = container_of(buffer, struct rpc_buffer, data);
        size = buf->len;

        dprintk("RPC:       freeing buffer of size %zu at %p\n",
                        size, buf);

        if (size <= RPC_BUFFER_MAXSIZE)
                mempool_free(buf, rpc_buffer_mempool);
        else
                kfree(buf);
}
EXPORT_SYMBOL_GPL(rpc_free);

/*
 * Creation and deletion of RPC task structures
 */
static void rpc_init_task(struct rpc_task *task, const struct rpc_task_setup *task_setup_data)
{
        memset(task, 0, sizeof(*task));
        atomic_set(&task->tk_count, 1);
        task->tk_flags  = task_setup_data->flags;
        task->tk_ops = task_setup_data->callback_ops;
        task->tk_calldata = task_setup_data->callback_data;
        INIT_LIST_HEAD(&task->tk_task);

        task->tk_priority = task_setup_data->priority - RPC_PRIORITY_LOW;
        task->tk_owner = current->tgid;

        /* Initialize workqueue for async tasks */
        task->tk_workqueue = task_setup_data->workqueue;

        task->tk_xprt = xprt_get(task_setup_data->rpc_xprt);

        if (task->tk_ops->rpc_call_prepare != NULL)
                task->tk_action = rpc_prepare_task;

        rpc_init_task_statistics(task);

        dprintk("RPC:       new task initialized, procpid %u\n",
                                task_pid_nr(current));
}

static struct rpc_task *
rpc_alloc_task(void)
{
        return (struct rpc_task *)mempool_alloc(rpc_task_mempool, GFP_NOIO);
}

/*
 * Create a new task for the specified client.
 */
struct rpc_task *rpc_new_task(const struct rpc_task_setup *setup_data)
{
        struct rpc_task *task = setup_data->task;
        unsigned short flags = 0;

        if (task == NULL) {
                task = rpc_alloc_task();
                if (task == NULL) {
                        rpc_release_calldata(setup_data->callback_ops,
                                        setup_data->callback_data);
                        return ERR_PTR(-ENOMEM);
                }
                flags = RPC_TASK_DYNAMIC;
        }

        rpc_init_task(task, setup_data);
        task->tk_flags |= flags;
        dprintk("RPC:       allocated task %p\n", task);
        return task;
}

/*
 * rpc_free_task - release rpc task and perform cleanups
 *
 * Note that we free up the rpc_task _after_ rpc_release_calldata()
 * in order to work around a workqueue dependency issue.
 *
 * Tejun Heo states:
 * "Workqueue currently considers two work items to be the same if they're
 * on the same address and won't execute them concurrently - ie. it
 * makes a work item which is queued again while being executed wait
 * for the previous execution to complete.
 *
 * If a work function frees the work item, and then waits for an event
 * which should be performed by another work item and *that* work item
 * recycles the freed work item, it can create a false dependency loop.
 * There really is no reliable way to detect this short of verifying
 * every memory free."
 *
 */
static void rpc_free_task(struct rpc_task *task)
{
        unsigned short tk_flags = task->tk_flags;

        rpc_release_calldata(task->tk_ops, task->tk_calldata);

        if (tk_flags & RPC_TASK_DYNAMIC) {
                dprintk("RPC: %5u freeing task\n", task->tk_pid);
                mempool_free(task, rpc_task_mempool);
        }
}

static void rpc_async_release(struct work_struct *work)
{
        rpc_free_task(container_of(work, struct rpc_task, u.tk_work));
}

static void rpc_release_resources_task(struct rpc_task *task)
{
        xprt_release(task);
        if (task->tk_msg.rpc_cred) {
                put_rpccred(task->tk_msg.rpc_cred);
                task->tk_msg.rpc_cred = NULL;
        }
        rpc_task_release_client(task);
}

static void rpc_final_put_task(struct rpc_task *task,
                struct workqueue_struct *q)
{
        if (q != NULL) {
                INIT_WORK(&task->u.tk_work, rpc_async_release);
                queue_work(q, &task->u.tk_work);
        } else
                rpc_free_task(task);
}

static void rpc_do_put_task(struct rpc_task *task, struct workqueue_struct *q)
{
        if (atomic_dec_and_test(&task->tk_count)) {
                rpc_release_resources_task(task);
                rpc_final_put_task(task, q);
        }
}

void rpc_put_task(struct rpc_task *task)
{
        rpc_do_put_task(task, NULL);
}
EXPORT_SYMBOL_GPL(rpc_put_task);

void rpc_put_task_async(struct rpc_task *task)
{
        rpc_do_put_task(task, task->tk_workqueue);
}
EXPORT_SYMBOL_GPL(rpc_put_task_async);

static void rpc_release_task(struct rpc_task *task)
{
        dprintk("RPC: %5u release task\n", task->tk_pid);

        WARN_ON_ONCE(RPC_IS_QUEUED(task));

        rpc_release_resources_task(task);

        /*
         * Note: at this point we have been removed from rpc_clnt->cl_tasks,
         * so it should be safe to use task->tk_count as a test for whether
         * or not any other processes still hold references to our rpc_task.
         */
        if (atomic_read(&task->tk_count) != 1 + !RPC_IS_ASYNC(task)) {
                /* Wake up anyone who may be waiting for task completion */
                if (!rpc_complete_task(task))
                        return;
        } else {
                if (!atomic_dec_and_test(&task->tk_count))
                        return;
        }
        rpc_final_put_task(task, task->tk_workqueue);
}

int rpciod_up(void)
{
        return try_module_get(THIS_MODULE) ? 0 : -EINVAL;
}

void rpciod_down(void)
{
        module_put(THIS_MODULE);
}

/*
 * Start up the rpciod workqueue.
 */
static int rpciod_start(void)
{
        struct workqueue_struct *wq;

        /*
         * Create the rpciod thread and wait for it to start.
         */
        dprintk("RPC:       creating workqueue rpciod\n");
        wq = alloc_workqueue("rpciod", WQ_MEM_RECLAIM, 0);
        if (!wq)
                goto out_failed;
        rpciod_workqueue = wq;
        /* Note: highpri because network receive is latency sensitive */
        wq = alloc_workqueue("xprtiod", WQ_MEM_RECLAIM | WQ_HIGHPRI, 0);
        if (!wq)
                goto free_rpciod;
        xprtiod_workqueue = wq;
        return 1;
free_rpciod:
        wq = rpciod_workqueue;
        rpciod_workqueue = NULL;
        destroy_workqueue(wq);
out_failed:
        return 0;
}

static void rpciod_stop(void)
{
        struct workqueue_struct *wq = NULL;

        if (rpciod_workqueue == NULL)
                return;
        dprintk("RPC:       destroying workqueue rpciod\n");

        wq = rpciod_workqueue;
        rpciod_workqueue = NULL;
        destroy_workqueue(wq);
        wq = xprtiod_workqueue;
        xprtiod_workqueue = NULL;
        destroy_workqueue(wq);
}

void
rpc_destroy_mempool(void)
{
        rpciod_stop();
        mempool_destroy(rpc_buffer_mempool);
        mempool_destroy(rpc_task_mempool);
        kmem_cache_destroy(rpc_task_slabp);
        kmem_cache_destroy(rpc_buffer_slabp);
        rpc_destroy_wait_queue(&delay_queue);
}

int
rpc_init_mempool(void)
{
        /*
         * The following is not strictly a mempool initialisation,
         * but there is no harm in doing it here
         */
        rpc_init_wait_queue(&delay_queue, "delayq");
        if (!rpciod_start())
                goto err_nomem;

        rpc_task_slabp = kmem_cache_create("rpc_tasks",
                                             sizeof(struct rpc_task),
                                             0, SLAB_HWCACHE_ALIGN,
                                             NULL);
        if (!rpc_task_slabp)
                goto err_nomem;
        rpc_buffer_slabp = kmem_cache_create("rpc_buffers",
                                             RPC_BUFFER_MAXSIZE,
                                             0, SLAB_HWCACHE_ALIGN,
                                             NULL);
        if (!rpc_buffer_slabp)
                goto err_nomem;
        rpc_task_mempool = mempool_create_slab_pool(RPC_TASK_POOLSIZE,
                                                    rpc_task_slabp);
        if (!rpc_task_mempool)
                goto err_nomem;
        rpc_buffer_mempool = mempool_create_slab_pool(RPC_BUFFER_POOLSIZE,
                                                      rpc_buffer_slabp);
        if (!rpc_buffer_mempool)
                goto err_nomem;
        return 0;
err_nomem:
        rpc_destroy_mempool();
        return -ENOMEM;
}