// SPDX-License-Identifier: GPL-2.0
/*
 * Basic worker thread pool for io_uring
 *
 * Copyright (C) 2019 Jens Axboe
 *
 */
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/errno.h>
#include <linux/sched/signal.h>
#include <linux/mm.h>
#include <linux/sched/mm.h>
#include <linux/percpu.h>
#include <linux/slab.h>
#include <linux/kthread.h>
#include <linux/rculist_nulls.h>
#include <linux/fs_struct.h>
#include <linux/task_work.h>

#include "io-wq.h"

#define WORKER_IDLE_TIMEOUT     (5 * HZ)

enum {
        IO_WORKER_F_UP          = 1,    /* up and active */
        IO_WORKER_F_RUNNING     = 2,    /* account as running */
        IO_WORKER_F_FREE        = 4,    /* worker on free list */
        IO_WORKER_F_EXITING     = 8,    /* worker exiting */
        IO_WORKER_F_FIXED       = 16,   /* static idle worker */
        IO_WORKER_F_BOUND       = 32,   /* is doing bounded work */
};

enum {
        IO_WQ_BIT_EXIT          = 0,    /* wq exiting */
        IO_WQ_BIT_CANCEL        = 1,    /* cancel work on list */
        IO_WQ_BIT_ERROR         = 2,    /* error on setup */
};

enum {
        IO_WQE_FLAG_STALLED     = 1,    /* stalled on hash */
};

/*
 * One for each thread in a wqe pool
 */
struct io_worker {
        refcount_t ref;
        unsigned flags;
        struct hlist_nulls_node nulls_node;
        struct list_head all_list;
        struct task_struct *task;
        struct io_wqe *wqe;

        struct io_wq_work *cur_work;
        spinlock_t lock;

        struct rcu_head rcu;
        struct mm_struct *mm;
        const struct cred *cur_creds;
        const struct cred *saved_creds;
        struct files_struct *restore_files;
        struct fs_struct *restore_fs;
};

#if BITS_PER_LONG == 64
#define IO_WQ_HASH_ORDER        6
#else
#define IO_WQ_HASH_ORDER        5
#endif

#define IO_WQ_NR_HASH_BUCKETS   (1u << IO_WQ_HASH_ORDER)

struct io_wqe_acct {
        unsigned nr_workers;
        unsigned max_workers;
        atomic_t nr_running;
};

enum {
        IO_WQ_ACCT_BOUND,
        IO_WQ_ACCT_UNBOUND,
};

/*
 * Per-node worker thread pool
 */
struct io_wqe {
        struct {
                spinlock_t lock;
                struct io_wq_work_list work_list;
                unsigned long hash_map;
                unsigned flags;
        } ____cacheline_aligned_in_smp;

        int node;
        struct io_wqe_acct acct[2];

        struct hlist_nulls_head free_list;
        struct list_head all_list;

        struct io_wq *wq;
        struct io_wq_work *hash_tail[IO_WQ_NR_HASH_BUCKETS];
};

/*
 * Per io_wq state
  */
struct io_wq {
        struct io_wqe **wqes;
        unsigned long state;

        free_work_fn *free_work;
        io_wq_work_fn *do_work;

        struct task_struct *manager;
        struct user_struct *user;
        refcount_t refs;
        struct completion done;

        refcount_t use_refs;
};

static bool io_worker_get(struct io_worker *worker)
{
        return refcount_inc_not_zero(&worker->ref);
}

static void io_worker_release(struct io_worker *worker)
{
        if (refcount_dec_and_test(&worker->ref))
                wake_up_process(worker->task);
}

/*
 * Note: drops the wqe->lock if returning true! The caller must re-acquire
 * the lock in that case. Some callers need to restart handling if this
 * happens, so we can't just re-acquire the lock on behalf of the caller.
 */
static bool __io_worker_unuse(struct io_wqe *wqe, struct io_worker *worker)
{
        bool dropped_lock = false;

        if (worker->saved_creds) {
                revert_creds(worker->saved_creds);
                worker->cur_creds = worker->saved_creds = NULL;
        }

        if (current->files != worker->restore_files) {
                __acquire(&wqe->lock);
                spin_unlock_irq(&wqe->lock);
                dropped_lock = true;

                task_lock(current);
                current->files = worker->restore_files;
                task_unlock(current);
        }

        if (current->fs != worker->restore_fs)
                current->fs = worker->restore_fs;

        /*
         * If we have an active mm, we need to drop the wq lock before unusing
         * it. If we do, return true and let the caller retry the idle loop.
         */
        if (worker->mm) {
                if (!dropped_lock) {
                        __acquire(&wqe->lock);
                        spin_unlock_irq(&wqe->lock);
                        dropped_lock = true;
                }
                __set_current_state(TASK_RUNNING);
                kthread_unuse_mm(worker->mm);
                mmput(worker->mm);
                worker->mm = NULL;
        }

        return dropped_lock;
}

static inline struct io_wqe_acct *io_work_get_acct(struct io_wqe *wqe,
                                                   struct io_wq_work *work)
{
        if (work->flags & IO_WQ_WORK_UNBOUND)
                return &wqe->acct[IO_WQ_ACCT_UNBOUND];

        return &wqe->acct[IO_WQ_ACCT_BOUND];
}

static inline struct io_wqe_acct *io_wqe_get_acct(struct io_wqe *wqe,
                                                  struct io_worker *worker)
{
        if (worker->flags & IO_WORKER_F_BOUND)
                return &wqe->acct[IO_WQ_ACCT_BOUND];

        return &wqe->acct[IO_WQ_ACCT_UNBOUND];
}

static void io_worker_exit(struct io_worker *worker)
{
        struct io_wqe *wqe = worker->wqe;
        struct io_wqe_acct *acct = io_wqe_get_acct(wqe, worker);
        unsigned nr_workers;

        /*
         * If we're not at zero, someone else is holding a brief reference
         * to the worker. Wait for that to go away.
         */
        set_current_state(TASK_INTERRUPTIBLE);
        if (!refcount_dec_and_test(&worker->ref))
                schedule();
        __set_current_state(TASK_RUNNING);

        preempt_disable();
        current->flags &= ~PF_IO_WORKER;
        if (worker->flags & IO_WORKER_F_RUNNING)
                atomic_dec(&acct->nr_running);
        if (!(worker->flags & IO_WORKER_F_BOUND))
                atomic_dec(&wqe->wq->user->processes);
        worker->flags = 0;
        preempt_enable();

        spin_lock_irq(&wqe->lock);
        hlist_nulls_del_rcu(&worker->nulls_node);
        list_del_rcu(&worker->all_list);
        if (__io_worker_unuse(wqe, worker)) {
                __release(&wqe->lock);
                spin_lock_irq(&wqe->lock);
        }
        acct->nr_workers--;
        nr_workers = wqe->acct[IO_WQ_ACCT_BOUND].nr_workers +
                        wqe->acct[IO_WQ_ACCT_UNBOUND].nr_workers;
        spin_unlock_irq(&wqe->lock);

        /* all workers gone, wq exit can proceed */
        if (!nr_workers && refcount_dec_and_test(&wqe->wq->refs))
                complete(&wqe->wq->done);

        kfree_rcu(worker, rcu);
}

static inline bool io_wqe_run_queue(struct io_wqe *wqe)
        __must_hold(wqe->lock)
{
        if (!wq_list_empty(&wqe->work_list) &&
            !(wqe->flags & IO_WQE_FLAG_STALLED))
                return true;
        return false;
}

/*
 * Check head of free list for an available worker. If one isn't available,
 * caller must wake up the wq manager to create one.
 */
static bool io_wqe_activate_free_worker(struct io_wqe *wqe)
        __must_hold(RCU)
{
        struct hlist_nulls_node *n;
        struct io_worker *worker;

        n = rcu_dereference(hlist_nulls_first_rcu(&wqe->free_list));
        if (is_a_nulls(n))
                return false;

        worker = hlist_nulls_entry(n, struct io_worker, nulls_node);
        if (io_worker_get(worker)) {
                wake_up_process(worker->task);
                io_worker_release(worker);
                return true;
        }

        return false;
}

/*
 * We need a worker. If we find a free one, we're good. If not, and we're
 * below the max number of workers, wake up the manager to create one.
 */
static void io_wqe_wake_worker(struct io_wqe *wqe, struct io_wqe_acct *acct)
{
        bool ret;

        /*
         * Most likely an attempt to queue unbounded work on an io_wq that
         * wasn't setup with any unbounded workers.
         */
        WARN_ON_ONCE(!acct->max_workers);

        rcu_read_lock();
        ret = io_wqe_activate_free_worker(wqe);
        rcu_read_unlock();

        if (!ret && acct->nr_workers < acct->max_workers)
                wake_up_process(wqe->wq->manager);
}

static void io_wqe_inc_running(struct io_wqe *wqe, struct io_worker *worker)
{
        struct io_wqe_acct *acct = io_wqe_get_acct(wqe, worker);

        atomic_inc(&acct->nr_running);
}

static void io_wqe_dec_running(struct io_wqe *wqe, struct io_worker *worker)
        __must_hold(wqe->lock)
{
        struct io_wqe_acct *acct = io_wqe_get_acct(wqe, worker);

        if (atomic_dec_and_test(&acct->nr_running) && io_wqe_run_queue(wqe))
                io_wqe_wake_worker(wqe, acct);
}

static void io_worker_start(struct io_wqe *wqe, struct io_worker *worker)
{
        allow_kernel_signal(SIGINT);

        current->flags |= PF_IO_WORKER;

        worker->flags |= (IO_WORKER_F_UP | IO_WORKER_F_RUNNING);
        worker->restore_files = current->files;
        worker->restore_fs = current->fs;
        io_wqe_inc_running(wqe, worker);
}

/*
 * Worker will start processing some work. Move it to the busy list, if
 * it's currently on the freelist
 */
static void __io_worker_busy(struct io_wqe *wqe, struct io_worker *worker,
                             struct io_wq_work *work)
        __must_hold(wqe->lock)
{
        bool worker_bound, work_bound;

        if (worker->flags & IO_WORKER_F_FREE) {
                worker->flags &= ~IO_WORKER_F_FREE;
                hlist_nulls_del_init_rcu(&worker->nulls_node);
        }

        /*
         * If worker is moving from bound to unbound (or vice versa), then
         * ensure we update the running accounting.
         */
        worker_bound = (worker->flags & IO_WORKER_F_BOUND) != 0;
        work_bound = (work->flags & IO_WQ_WORK_UNBOUND) == 0;
        if (worker_bound != work_bound) {
                io_wqe_dec_running(wqe, worker);
                if (work_bound) {
                        worker->flags |= IO_WORKER_F_BOUND;
                        wqe->acct[IO_WQ_ACCT_UNBOUND].nr_workers--;
                        wqe->acct[IO_WQ_ACCT_BOUND].nr_workers++;
                        atomic_dec(&wqe->wq->user->processes);
                } else {
                        worker->flags &= ~IO_WORKER_F_BOUND;
                        wqe->acct[IO_WQ_ACCT_UNBOUND].nr_workers++;
                        wqe->acct[IO_WQ_ACCT_BOUND].nr_workers--;
                        atomic_inc(&wqe->wq->user->processes);
                }
                io_wqe_inc_running(wqe, worker);
         }
}

/*
 * No work, worker going to sleep. Move to freelist, and unuse mm if we
 * have one attached. Dropping the mm may potentially sleep, so we drop
 * the lock in that case and return success. Since the caller has to
 * retry the loop in that case (we changed task state), we don't regrab
 * the lock if we return success.
 */
static bool __io_worker_idle(struct io_wqe *wqe, struct io_worker *worker)
        __must_hold(wqe->lock)
{
        if (!(worker->flags & IO_WORKER_F_FREE)) {
                worker->flags |= IO_WORKER_F_FREE;
                hlist_nulls_add_head_rcu(&worker->nulls_node, &wqe->free_list);
        }

        return __io_worker_unuse(wqe, worker);
}

static inline unsigned int io_get_work_hash(struct io_wq_work *work)
{
        return work->flags >> IO_WQ_HASH_SHIFT;
}

static struct io_wq_work *io_get_next_work(struct io_wqe *wqe)
        __must_hold(wqe->lock)
{
        struct io_wq_work_node *node, *prev;
        struct io_wq_work *work, *tail;
        unsigned int hash;

        wq_list_for_each(node, prev, &wqe->work_list) {
                work = container_of(node, struct io_wq_work, list);

                /* not hashed, can run anytime */
                if (!io_wq_is_hashed(work)) {
                        wq_list_del(&wqe->work_list, node, prev);
                        return work;
                }

                /* hashed, can run if not already running */
                hash = io_get_work_hash(work);
                if (!(wqe->hash_map & BIT(hash))) {
                        wqe->hash_map |= BIT(hash);
                        /* all items with this hash lie in [work, tail] */
                        tail = wqe->hash_tail[hash];
                        wqe->hash_tail[hash] = NULL;
                        wq_list_cut(&wqe->work_list, &tail->list, prev);
                        return work;
                }
        }

        return NULL;
}

static void io_wq_switch_mm(struct io_worker *worker, struct io_wq_work *work)
{
        if (worker->mm) {
                kthread_unuse_mm(worker->mm);
                mmput(worker->mm);
                worker->mm = NULL;
        }
        if (!work->mm)
                return;

        if (mmget_not_zero(work->mm)) {
                kthread_use_mm(work->mm);
                worker->mm = work->mm;
                /* hang on to this mm */
                work->mm = NULL;
                return;
        }

        /* failed grabbing mm, ensure work gets cancelled */
        work->flags |= IO_WQ_WORK_CANCEL;
}

static void io_wq_switch_creds(struct io_worker *worker,
                               struct io_wq_work *work)
{
        const struct cred *old_creds = override_creds(work->creds);

        worker->cur_creds = work->creds;
        if (worker->saved_creds)
                put_cred(old_creds); /* creds set by previous switch */
        else
                worker->saved_creds = old_creds;
}

static void io_impersonate_work(struct io_worker *worker,
                                struct io_wq_work *work)
{
        if (work->files && current->files != work->files) {
                task_lock(current);
                current->files = work->files;
                task_unlock(current);
        }
        if (work->fs && current->fs != work->fs)
                current->fs = work->fs;
        if (work->mm != worker->mm)
                io_wq_switch_mm(worker, work);
        if (worker->cur_creds != work->creds)
                io_wq_switch_creds(worker, work);
}

static void io_assign_current_work(struct io_worker *worker,
                                   struct io_wq_work *work)
{
        if (work) {
                /* flush pending signals before assigning new work */
                if (signal_pending(current))
                        flush_signals(current);
                cond_resched();
        }

        spin_lock_irq(&worker->lock);
        worker->cur_work = work;
        spin_unlock_irq(&worker->lock);
}

static void io_wqe_enqueue(struct io_wqe *wqe, struct io_wq_work *work);

static void io_worker_handle_work(struct io_worker *worker)
        __releases(wqe->lock)
{
        struct io_wqe *wqe = worker->wqe;
        struct io_wq *wq = wqe->wq;

        do {
                struct io_wq_work *work;
                unsigned int hash;
get_next:
                /*
                 * If we got some work, mark us as busy. If we didn't, but
                 * the list isn't empty, it means we stalled on hashed work.
                 * Mark us stalled so we don't keep looking for work when we
                 * can't make progress, any work completion or insertion will
                 * clear the stalled flag.
                 */
                work = io_get_next_work(wqe);
                if (work)
                        __io_worker_busy(wqe, worker, work);
                else if (!wq_list_empty(&wqe->work_list))
                        wqe->flags |= IO_WQE_FLAG_STALLED;

                spin_unlock_irq(&wqe->lock);
                if (!work)
                        break;
                io_assign_current_work(worker, work);

                /* handle a whole dependent link */
                do {
                        struct io_wq_work *old_work, *next_hashed, *linked;

                        next_hashed = wq_next_work(work);
                        io_impersonate_work(worker, work);
                        /*
                         * OK to set IO_WQ_WORK_CANCEL even for uncancellable
                         * work, the worker function will do the right thing.
                         */
                        if (test_bit(IO_WQ_BIT_CANCEL, &wq->state))
                                work->flags |= IO_WQ_WORK_CANCEL;

                        hash = io_get_work_hash(work);
                        linked = old_work = work;
                        wq->do_work(&linked);
                        linked = (old_work == linked) ? NULL : linked;

                        work = next_hashed;
                        if (!work && linked && !io_wq_is_hashed(linked)) {
                                work = linked;
                                linked = NULL;
                        }
                        io_assign_current_work(worker, work);
                        wq->free_work(old_work);

                        if (linked)
                                io_wqe_enqueue(wqe, linked);

                        if (hash != -1U && !next_hashed) {
                                spin_lock_irq(&wqe->lock);
                                wqe->hash_map &= ~BIT_ULL(hash);
                                wqe->flags &= ~IO_WQE_FLAG_STALLED;
                                /* dependent work is not hashed */
                                hash = -1U;
                                /* skip unnecessary unlock-lock wqe->lock */
                                if (!work)
                                        goto get_next;
                                spin_unlock_irq(&wqe->lock);
                        }
                } while (work);

                spin_lock_irq(&wqe->lock);
        } while (1);
}

static int io_wqe_worker(void *data)
{
        struct io_worker *worker = data;
        struct io_wqe *wqe = worker->wqe;
        struct io_wq *wq = wqe->wq;

        io_worker_start(wqe, worker);

        while (!test_bit(IO_WQ_BIT_EXIT, &wq->state)) {
                set_current_state(TASK_INTERRUPTIBLE);
loop:
                spin_lock_irq(&wqe->lock);
                if (io_wqe_run_queue(wqe)) {
                        __set_current_state(TASK_RUNNING);
                        io_worker_handle_work(worker);
                        goto loop;
                }
                /* drops the lock on success, retry */
                if (__io_worker_idle(wqe, worker)) {
                        __release(&wqe->lock);
                        goto loop;
                }
                spin_unlock_irq(&wqe->lock);
                if (signal_pending(current))
                        flush_signals(current);
                if (schedule_timeout(WORKER_IDLE_TIMEOUT))
                        continue;
                /* timed out, exit unless we're the fixed worker */
                if (test_bit(IO_WQ_BIT_EXIT, &wq->state) ||
                    !(worker->flags & IO_WORKER_F_FIXED))
                        break;
        }

        if (test_bit(IO_WQ_BIT_EXIT, &wq->state)) {
                spin_lock_irq(&wqe->lock);
                if (!wq_list_empty(&wqe->work_list))
                        io_worker_handle_work(worker);
                else
                        spin_unlock_irq(&wqe->lock);
        }

        io_worker_exit(worker);
        return 0;
}

/*
 * Called when a worker is scheduled in. Mark us as currently running.
 */
void io_wq_worker_running(struct task_struct *tsk)
{
        struct io_worker *worker = kthread_data(tsk);
        struct io_wqe *wqe = worker->wqe;

        if (!(worker->flags & IO_WORKER_F_UP))
                return;
        if (worker->flags & IO_WORKER_F_RUNNING)
                return;
        worker->flags |= IO_WORKER_F_RUNNING;
        io_wqe_inc_running(wqe, worker);
}

/*
 * Called when worker is going to sleep. If there are no workers currently
 * running and we have work pending, wake up a free one or have the manager
 * set one up.
 */
void io_wq_worker_sleeping(struct task_struct *tsk)
{
        struct io_worker *worker = kthread_data(tsk);
        struct io_wqe *wqe = worker->wqe;

        if (!(worker->flags & IO_WORKER_F_UP))
                return;
        if (!(worker->flags & IO_WORKER_F_RUNNING))
                return;

        worker->flags &= ~IO_WORKER_F_RUNNING;

        spin_lock_irq(&wqe->lock);
        io_wqe_dec_running(wqe, worker);
        spin_unlock_irq(&wqe->lock);
}

static bool create_io_worker(struct io_wq *wq, struct io_wqe *wqe, int index)
{
        struct io_wqe_acct *acct =&wqe->acct[index];
        struct io_worker *worker;

        worker = kzalloc_node(sizeof(*worker), GFP_KERNEL, wqe->node);
        if (!worker)
                return false;

        refcount_set(&worker->ref, 1);
        worker->nulls_node.pprev = NULL;
        worker->wqe = wqe;
        spin_lock_init(&worker->lock);

        worker->task = kthread_create_on_node(io_wqe_worker, worker, wqe->node,
                                "io_wqe_worker-%d/%d", index, wqe->node);
        if (IS_ERR(worker->task)) {
                kfree(worker);
                return false;
        }

        spin_lock_irq(&wqe->lock);
        hlist_nulls_add_head_rcu(&worker->nulls_node, &wqe->free_list);
        list_add_tail_rcu(&worker->all_list, &wqe->all_list);
        worker->flags |= IO_WORKER_F_FREE;
        if (index == IO_WQ_ACCT_BOUND)
                worker->flags |= IO_WORKER_F_BOUND;
        if (!acct->nr_workers && (worker->flags & IO_WORKER_F_BOUND))
                worker->flags |= IO_WORKER_F_FIXED;
        acct->nr_workers++;
        spin_unlock_irq(&wqe->lock);

        if (index == IO_WQ_ACCT_UNBOUND)
                atomic_inc(&wq->user->processes);

        wake_up_process(worker->task);
        return true;
}

static inline bool io_wqe_need_worker(struct io_wqe *wqe, int index)
        __must_hold(wqe->lock)
{
        struct io_wqe_acct *acct = &wqe->acct[index];

        /* if we have available workers or no work, no need */
        if (!hlist_nulls_empty(&wqe->free_list) || !io_wqe_run_queue(wqe))
                return false;
        return acct->nr_workers < acct->max_workers;
}

/*
 * Manager thread. Tasked with creating new workers, if we need them.
 */
static int io_wq_manager(void *data)
{
        struct io_wq *wq = data;
        int workers_to_create = num_possible_nodes();
        int node;

        /* create fixed workers */
        refcount_set(&wq->refs, workers_to_create);
        for_each_node(node) {
                if (!node_online(node))
                        continue;
                if (!create_io_worker(wq, wq->wqes[node], IO_WQ_ACCT_BOUND))
                        goto err;
                workers_to_create--;
        }

        while (workers_to_create--)
                refcount_dec(&wq->refs);

        complete(&wq->done);

        while (!kthread_should_stop()) {
                if (current->task_works)
                        task_work_run();

                for_each_node(node) {
                        struct io_wqe *wqe = wq->wqes[node];
                        bool fork_worker[2] = { false, false };

                        if (!node_online(node))
                                continue;

                        spin_lock_irq(&wqe->lock);
                        if (io_wqe_need_worker(wqe, IO_WQ_ACCT_BOUND))
                                fork_worker[IO_WQ_ACCT_BOUND] = true;
                        if (io_wqe_need_worker(wqe, IO_WQ_ACCT_UNBOUND))
                                fork_worker[IO_WQ_ACCT_UNBOUND] = true;
                        spin_unlock_irq(&wqe->lock);
                        if (fork_worker[IO_WQ_ACCT_BOUND])
                                create_io_worker(wq, wqe, IO_WQ_ACCT_BOUND);
                        if (fork_worker[IO_WQ_ACCT_UNBOUND])
                                create_io_worker(wq, wqe, IO_WQ_ACCT_UNBOUND);
                }
                set_current_state(TASK_INTERRUPTIBLE);
                schedule_timeout(HZ);
        }

        if (current->task_works)
                task_work_run();

        return 0;
err:
        set_bit(IO_WQ_BIT_ERROR, &wq->state);
        set_bit(IO_WQ_BIT_EXIT, &wq->state);
        if (refcount_sub_and_test(workers_to_create, &wq->refs))
                complete(&wq->done);
        return 0;
}

static bool io_wq_can_queue(struct io_wqe *wqe, struct io_wqe_acct *acct,
                            struct io_wq_work *work)
{
        bool free_worker;

        if (!(work->flags & IO_WQ_WORK_UNBOUND))
                return true;
        if (atomic_read(&acct->nr_running))
                return true;

        rcu_read_lock();
        free_worker = !hlist_nulls_empty(&wqe->free_list);
        rcu_read_unlock();
        if (free_worker)
                return true;

        if (atomic_read(&wqe->wq->user->processes) >= acct->max_workers &&
            !(capable(CAP_SYS_RESOURCE) || capable(CAP_SYS_ADMIN)))
                return false;

        return true;
}

static void io_run_cancel(struct io_wq_work *work, struct io_wqe *wqe)
{
        struct io_wq *wq = wqe->wq;

        do {
                struct io_wq_work *old_work = work;

                work->flags |= IO_WQ_WORK_CANCEL;
                wq->do_work(&work);
                work = (work == old_work) ? NULL : work;
                wq->free_work(old_work);
        } while (work);
}

static void io_wqe_insert_work(struct io_wqe *wqe, struct io_wq_work *work)
{
        unsigned int hash;
        struct io_wq_work *tail;

        if (!io_wq_is_hashed(work)) {
append:
                wq_list_add_tail(&work->list, &wqe->work_list);
                return;
        }

        hash = io_get_work_hash(work);
        tail = wqe->hash_tail[hash];
        wqe->hash_tail[hash] = work;
        if (!tail)
                goto append;

        wq_list_add_after(&work->list, &tail->list, &wqe->work_list);
}

static void io_wqe_enqueue(struct io_wqe *wqe, struct io_wq_work *work)
{
        struct io_wqe_acct *acct = io_work_get_acct(wqe, work);
        int work_flags;
        unsigned long flags;

        /*
         * Do early check to see if we need a new unbound worker, and if we do,
         * if we're allowed to do so. This isn't 100% accurate as there's a
         * gap between this check and incrementing the value, but that's OK.
         * It's close enough to not be an issue, fork() has the same delay.
         */
        if (unlikely(!io_wq_can_queue(wqe, acct, work))) {
                io_run_cancel(work, wqe);
                return;
        }

        work_flags = work->flags;
        spin_lock_irqsave(&wqe->lock, flags);
        io_wqe_insert_work(wqe, work);
        wqe->flags &= ~IO_WQE_FLAG_STALLED;
        spin_unlock_irqrestore(&wqe->lock, flags);

        if ((work_flags & IO_WQ_WORK_CONCURRENT) ||
            !atomic_read(&acct->nr_running))
                io_wqe_wake_worker(wqe, acct);
}

void io_wq_enqueue(struct io_wq *wq, struct io_wq_work *work)
{
        struct io_wqe *wqe = wq->wqes[numa_node_id()];

        io_wqe_enqueue(wqe, work);
}

/*
 * Work items that hash to the same value will not be done in parallel.
 * Used to limit concurrent writes, generally hashed by inode.
 */
void io_wq_hash_work(struct io_wq_work *work, void *val)
{
        unsigned int bit;

        bit = hash_ptr(val, IO_WQ_HASH_ORDER);
        work->flags |= (IO_WQ_WORK_HASHED | (bit << IO_WQ_HASH_SHIFT));
}

static bool io_wqe_worker_send_sig(struct io_worker *worker, void *data)
{
        send_sig(SIGINT, worker->task, 1);
        return false;
}

/*
 * Iterate the passed in list and call the specific function for each
 * worker that isn't exiting
 */
static bool io_wq_for_each_worker(struct io_wqe *wqe,
                                  bool (*func)(struct io_worker *, void *),
                                  void *data)
{
        struct io_worker *worker;
        bool ret = false;

        list_for_each_entry_rcu(worker, &wqe->all_list, all_list) {
                if (io_worker_get(worker)) {
                        /* no task if node is/was offline */
                        if (worker->task)
                                ret = func(worker, data);
                        io_worker_release(worker);
                        if (ret)
                                break;
                }
        }

        return ret;
}

void io_wq_cancel_all(struct io_wq *wq)
{
        int node;

        set_bit(IO_WQ_BIT_CANCEL, &wq->state);

        rcu_read_lock();
        for_each_node(node) {
                struct io_wqe *wqe = wq->wqes[node];

                io_wq_for_each_worker(wqe, io_wqe_worker_send_sig, NULL);
        }
        rcu_read_unlock();
}

struct io_cb_cancel_data {
        work_cancel_fn *fn;
        void *data;
        int nr_running;
        int nr_pending;
        bool cancel_all;
};

static bool io_wq_worker_cancel(struct io_worker *worker, void *data)
{
        struct io_cb_cancel_data *match = data;
        unsigned long flags;

        /*
         * Hold the lock to avoid ->cur_work going out of scope, caller
         * may dereference the passed in work.
         */
        spin_lock_irqsave(&worker->lock, flags);
        if (worker->cur_work &&
            !(worker->cur_work->flags & IO_WQ_WORK_NO_CANCEL) &&
            match->fn(worker->cur_work, match->data)) {
                send_sig(SIGINT, worker->task, 1);
                match->nr_running++;
        }
        spin_unlock_irqrestore(&worker->lock, flags);

        return match->nr_running && !match->cancel_all;
}

static void io_wqe_cancel_pending_work(struct io_wqe *wqe,
                                       struct io_cb_cancel_data *match)
{
        struct io_wq_work_node *node, *prev;
        struct io_wq_work *work;
        unsigned long flags;

retry:
        spin_lock_irqsave(&wqe->lock, flags);
        wq_list_for_each(node, prev, &wqe->work_list) {
                work = container_of(node, struct io_wq_work, list);
                if (!match->fn(work, match->data))
                        continue;

                wq_list_del(&wqe->work_list, node, prev);
                spin_unlock_irqrestore(&wqe->lock, flags);
                io_run_cancel(work, wqe);
                match->nr_pending++;
                if (!match->cancel_all)
                        return;

                /* not safe to continue after unlock */
                goto retry;
        }
        spin_unlock_irqrestore(&wqe->lock, flags);
}

static void io_wqe_cancel_running_work(struct io_wqe *wqe,
                                       struct io_cb_cancel_data *match)
{
        rcu_read_lock();
        io_wq_for_each_worker(wqe, io_wq_worker_cancel, match);
        rcu_read_unlock();
}

enum io_wq_cancel io_wq_cancel_cb(struct io_wq *wq, work_cancel_fn *cancel,
                                  void *data, bool cancel_all)
{
        struct io_cb_cancel_data match = {
                .fn             = cancel,
                .data           = data,
                .cancel_all     = cancel_all,
        };
        int node;

        /*
         * First check pending list, if we're lucky we can just remove it
         * from there. CANCEL_OK means that the work is returned as-new,
         * no completion will be posted for it.
         */
        for_each_node(node) {
                struct io_wqe *wqe = wq->wqes[node];

                io_wqe_cancel_pending_work(wqe, &match);
                if (match.nr_pending && !match.cancel_all)
                        return IO_WQ_CANCEL_OK;
        }

        /*
         * Now check if a free (going busy) or busy worker has the work
         * currently running. If we find it there, we'll return CANCEL_RUNNING
         * as an indication that we attempt to signal cancellation. The
         * completion will run normally in this case.
         */
        for_each_node(node) {
                struct io_wqe *wqe = wq->wqes[node];

                io_wqe_cancel_running_work(wqe, &match);
                if (match.nr_running && !match.cancel_all)

                        return IO_WQ_CANCEL_RUNNING;
        }

        if (match.nr_running)
                return IO_WQ_CANCEL_RUNNING;
        if (match.nr_pending)
                return IO_WQ_CANCEL_OK;
        return IO_WQ_CANCEL_NOTFOUND;
}

static bool io_wq_io_cb_cancel_data(struct io_wq_work *work, void *data)
{
        return work == data;
}

enum io_wq_cancel io_wq_cancel_work(struct io_wq *wq, struct io_wq_work *cwork)
{
        return io_wq_cancel_cb(wq, io_wq_io_cb_cancel_data, (void *)cwork, false);
}

struct io_wq *io_wq_create(unsigned bounded, struct io_wq_data *data)
{
        int ret = -ENOMEM, node;
        struct io_wq *wq;

        if (WARN_ON_ONCE(!data->free_work || !data->do_work))
                return ERR_PTR(-EINVAL);

        wq = kzalloc(sizeof(*wq), GFP_KERNEL);
        if (!wq)
                return ERR_PTR(-ENOMEM);

        wq->wqes = kcalloc(nr_node_ids, sizeof(struct io_wqe *), GFP_KERNEL);
        if (!wq->wqes) {
                kfree(wq);
                return ERR_PTR(-ENOMEM);
        }

        wq->free_work = data->free_work;
        wq->do_work = data->do_work;

        /* caller must already hold a reference to this */
        wq->user = data->user;

        for_each_node(node) {
                struct io_wqe *wqe;
                int alloc_node = node;

                if (!node_online(alloc_node))
                        alloc_node = NUMA_NO_NODE;
                wqe = kzalloc_node(sizeof(struct io_wqe), GFP_KERNEL, alloc_node);
                if (!wqe)
                        goto err;
                wq->wqes[node] = wqe;
                wqe->node = alloc_node;
                wqe->acct[IO_WQ_ACCT_BOUND].max_workers = bounded;
                atomic_set(&wqe->acct[IO_WQ_ACCT_BOUND].nr_running, 0);
                if (wq->user) {
                        wqe->acct[IO_WQ_ACCT_UNBOUND].max_workers =
                                        task_rlimit(current, RLIMIT_NPROC);
                }
                atomic_set(&wqe->acct[IO_WQ_ACCT_UNBOUND].nr_running, 0);
                wqe->wq = wq;
                spin_lock_init(&wqe->lock);
                INIT_WQ_LIST(&wqe->work_list);
                INIT_HLIST_NULLS_HEAD(&wqe->free_list, 0);
                INIT_LIST_HEAD(&wqe->all_list);
        }

        init_completion(&wq->done);

        wq->manager = kthread_create(io_wq_manager, wq, "io_wq_manager");
        if (!IS_ERR(wq->manager)) {
                wake_up_process(wq->manager);
                wait_for_completion(&wq->done);
                if (test_bit(IO_WQ_BIT_ERROR, &wq->state)) {
                        ret = -ENOMEM;
                        goto err;
                }
                refcount_set(&wq->use_refs, 1);
                reinit_completion(&wq->done);
                return wq;
        }

        ret = PTR_ERR(wq->manager);
        complete(&wq->done);
err:
        for_each_node(node)
                kfree(wq->wqes[node]);
        kfree(wq->wqes);
        kfree(wq);
        return ERR_PTR(ret);
}

bool io_wq_get(struct io_wq *wq, struct io_wq_data *data)
{
        if (data->free_work != wq->free_work || data->do_work != wq->do_work)
                return false;

        return refcount_inc_not_zero(&wq->use_refs);
}

static bool io_wq_worker_wake(struct io_worker *worker, void *data)
{
        wake_up_process(worker->task);
        return false;
}

static void __io_wq_destroy(struct io_wq *wq)
{
        int node;

        set_bit(IO_WQ_BIT_EXIT, &wq->state);
        if (wq->manager)
                kthread_stop(wq->manager);

        rcu_read_lock();
        for_each_node(node)
                io_wq_for_each_worker(wq->wqes[node], io_wq_worker_wake, NULL);
        rcu_read_unlock();

        wait_for_completion(&wq->done);

        for_each_node(node)
                kfree(wq->wqes[node]);
        kfree(wq->wqes);
        kfree(wq);
}

void io_wq_destroy(struct io_wq *wq)
{
        if (refcount_dec_and_test(&wq->use_refs))
                __io_wq_destroy(wq);
}

struct task_struct *io_wq_get_task(struct io_wq *wq)
{
        return wq->manager;
}