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

[drm/drm-misc.git] / io_uring / io-wq.c

// 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/percpu.h>
#include <linux/slab.h>
#include <linux/rculist_nulls.h>
#include <linux/cpu.h>
#include <linux/cpuset.h>
#include <linux/task_work.h>
#include <linux/audit.h>
#include <linux/mmu_context.h>
#include <uapi/linux/io_uring.h>

#include "io-wq.h"
#include "slist.h"
#include "io_uring.h"

#define WORKER_IDLE_TIMEOUT     (5 * HZ)
#define WORKER_INIT_LIMIT       3

enum {
        IO_WORKER_F_UP          = 0,    /* up and active */
        IO_WORKER_F_RUNNING     = 1,    /* account as running */
        IO_WORKER_F_FREE        = 2,    /* worker on free list */
        IO_WORKER_F_BOUND       = 3,    /* is doing bounded work */
};

enum {
        IO_WQ_BIT_EXIT          = 0,    /* wq exiting */
};

enum {
        IO_ACCT_STALLED_BIT     = 0,    /* stalled on hash */
};

/*
 * One for each thread in a wq pool
 */
struct io_worker {
        refcount_t ref;
        int create_index;
        unsigned long flags;
        struct hlist_nulls_node nulls_node;
        struct list_head all_list;
        struct task_struct *task;
        struct io_wq *wq;

        struct io_wq_work *cur_work;
        raw_spinlock_t lock;

        struct completion ref_done;

        unsigned long create_state;
        struct callback_head create_work;
        int init_retries;

        union {
                struct rcu_head rcu;
                struct work_struct work;
        };
};

#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_wq_acct {
        unsigned nr_workers;
        unsigned max_workers;
        int index;
        atomic_t nr_running;
        raw_spinlock_t lock;
        struct io_wq_work_list work_list;
        unsigned long flags;
};

enum {
        IO_WQ_ACCT_BOUND,
        IO_WQ_ACCT_UNBOUND,
        IO_WQ_ACCT_NR,
};

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

        free_work_fn *free_work;
        io_wq_work_fn *do_work;

        struct io_wq_hash *hash;

        atomic_t worker_refs;
        struct completion worker_done;

        struct hlist_node cpuhp_node;

        struct task_struct *task;

        struct io_wq_acct acct[IO_WQ_ACCT_NR];

        /* lock protects access to elements below */
        raw_spinlock_t lock;

        struct hlist_nulls_head free_list;
        struct list_head all_list;

        struct wait_queue_entry wait;

        struct io_wq_work *hash_tail[IO_WQ_NR_HASH_BUCKETS];

        cpumask_var_t cpu_mask;
};

static enum cpuhp_state io_wq_online;

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

static bool create_io_worker(struct io_wq *wq, int index);
static void io_wq_dec_running(struct io_worker *worker);
static bool io_acct_cancel_pending_work(struct io_wq *wq,
                                        struct io_wq_acct *acct,
                                        struct io_cb_cancel_data *match);
static void create_worker_cb(struct callback_head *cb);
static void io_wq_cancel_tw_create(struct io_wq *wq);

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))
                complete(&worker->ref_done);
}

static inline struct io_wq_acct *io_get_acct(struct io_wq *wq, bool bound)
{
        return &wq->acct[bound ? IO_WQ_ACCT_BOUND : IO_WQ_ACCT_UNBOUND];
}

static inline struct io_wq_acct *io_work_get_acct(struct io_wq *wq,
                                                  struct io_wq_work *work)
{
        return io_get_acct(wq, !(atomic_read(&work->flags) & IO_WQ_WORK_UNBOUND));
}

static inline struct io_wq_acct *io_wq_get_acct(struct io_worker *worker)
{
        return io_get_acct(worker->wq, test_bit(IO_WORKER_F_BOUND, &worker->flags));
}

static void io_worker_ref_put(struct io_wq *wq)
{
        if (atomic_dec_and_test(&wq->worker_refs))
                complete(&wq->worker_done);
}

bool io_wq_worker_stopped(void)
{
        struct io_worker *worker = current->worker_private;

        if (WARN_ON_ONCE(!io_wq_current_is_worker()))
                return true;

        return test_bit(IO_WQ_BIT_EXIT, &worker->wq->state);
}

static void io_worker_cancel_cb(struct io_worker *worker)
{
        struct io_wq_acct *acct = io_wq_get_acct(worker);
        struct io_wq *wq = worker->wq;

        atomic_dec(&acct->nr_running);
        raw_spin_lock(&wq->lock);
        acct->nr_workers--;
        raw_spin_unlock(&wq->lock);
        io_worker_ref_put(wq);
        clear_bit_unlock(0, &worker->create_state);
        io_worker_release(worker);
}

static bool io_task_worker_match(struct callback_head *cb, void *data)
{
        struct io_worker *worker;

        if (cb->func != create_worker_cb)
                return false;
        worker = container_of(cb, struct io_worker, create_work);
        return worker == data;
}

static void io_worker_exit(struct io_worker *worker)
{
        struct io_wq *wq = worker->wq;

        while (1) {
                struct callback_head *cb = task_work_cancel_match(wq->task,
                                                io_task_worker_match, worker);

                if (!cb)
                        break;
                io_worker_cancel_cb(worker);
        }

        io_worker_release(worker);
        wait_for_completion(&worker->ref_done);

        raw_spin_lock(&wq->lock);
        if (test_bit(IO_WORKER_F_FREE, &worker->flags))
                hlist_nulls_del_rcu(&worker->nulls_node);
        list_del_rcu(&worker->all_list);
        raw_spin_unlock(&wq->lock);
        io_wq_dec_running(worker);
        /*
         * this worker is a goner, clear ->worker_private to avoid any
         * inc/dec running calls that could happen as part of exit from
         * touching 'worker'.
         */
        current->worker_private = NULL;

        kfree_rcu(worker, rcu);
        io_worker_ref_put(wq);
        do_exit(0);
}

static inline bool __io_acct_run_queue(struct io_wq_acct *acct)
{
        return !test_bit(IO_ACCT_STALLED_BIT, &acct->flags) &&
                !wq_list_empty(&acct->work_list);
}

/*
 * If there's work to do, returns true with acct->lock acquired. If not,
 * returns false with no lock held.
 */
static inline bool io_acct_run_queue(struct io_wq_acct *acct)
        __acquires(&acct->lock)
{
        raw_spin_lock(&acct->lock);
        if (__io_acct_run_queue(acct))
                return true;

        raw_spin_unlock(&acct->lock);
        return false;
}

/*
 * Check head of free list for an available worker. If one isn't available,
 * caller must create one.
 */
static bool io_wq_activate_free_worker(struct io_wq *wq,
                                        struct io_wq_acct *acct)
        __must_hold(RCU)
{
        struct hlist_nulls_node *n;
        struct io_worker *worker;

        /*
         * Iterate free_list and see if we can find an idle worker to
         * activate. If a given worker is on the free_list but in the process
         * of exiting, keep trying.
         */
        hlist_nulls_for_each_entry_rcu(worker, n, &wq->free_list, nulls_node) {
                if (!io_worker_get(worker))
                        continue;
                if (io_wq_get_acct(worker) != acct) {
                        io_worker_release(worker);
                        continue;
                }
                /*
                 * If the worker is already running, it's either already
                 * starting work or finishing work. In either case, if it does
                 * to go sleep, we'll kick off a new task for this work anyway.
                 */
                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, create one.
 */
static bool io_wq_create_worker(struct io_wq *wq, struct io_wq_acct *acct)
{
        /*
         * Most likely an attempt to queue unbounded work on an io_wq that
         * wasn't setup with any unbounded workers.
         */
        if (unlikely(!acct->max_workers))
                pr_warn_once("io-wq is not configured for unbound workers");

        raw_spin_lock(&wq->lock);
        if (acct->nr_workers >= acct->max_workers) {
                raw_spin_unlock(&wq->lock);
                return true;
        }
        acct->nr_workers++;
        raw_spin_unlock(&wq->lock);
        atomic_inc(&acct->nr_running);
        atomic_inc(&wq->worker_refs);
        return create_io_worker(wq, acct->index);
}

static void io_wq_inc_running(struct io_worker *worker)
{
        struct io_wq_acct *acct = io_wq_get_acct(worker);

        atomic_inc(&acct->nr_running);
}

static void create_worker_cb(struct callback_head *cb)
{
        struct io_worker *worker;
        struct io_wq *wq;

        struct io_wq_acct *acct;
        bool do_create = false;

        worker = container_of(cb, struct io_worker, create_work);
        wq = worker->wq;
        acct = &wq->acct[worker->create_index];
        raw_spin_lock(&wq->lock);

        if (acct->nr_workers < acct->max_workers) {
                acct->nr_workers++;
                do_create = true;
        }
        raw_spin_unlock(&wq->lock);
        if (do_create) {
                create_io_worker(wq, worker->create_index);
        } else {
                atomic_dec(&acct->nr_running);
                io_worker_ref_put(wq);
        }
        clear_bit_unlock(0, &worker->create_state);
        io_worker_release(worker);
}

static bool io_queue_worker_create(struct io_worker *worker,
                                   struct io_wq_acct *acct,
                                   task_work_func_t func)
{
        struct io_wq *wq = worker->wq;

        /* raced with exit, just ignore create call */
        if (test_bit(IO_WQ_BIT_EXIT, &wq->state))
                goto fail;
        if (!io_worker_get(worker))
                goto fail;
        /*
         * create_state manages ownership of create_work/index. We should
         * only need one entry per worker, as the worker going to sleep
         * will trigger the condition, and waking will clear it once it
         * runs the task_work.
         */
        if (test_bit(0, &worker->create_state) ||
            test_and_set_bit_lock(0, &worker->create_state))
                goto fail_release;

        atomic_inc(&wq->worker_refs);
        init_task_work(&worker->create_work, func);
        worker->create_index = acct->index;
        if (!task_work_add(wq->task, &worker->create_work, TWA_SIGNAL)) {
                /*
                 * EXIT may have been set after checking it above, check after
                 * adding the task_work and remove any creation item if it is
                 * now set. wq exit does that too, but we can have added this
                 * work item after we canceled in io_wq_exit_workers().
                 */
                if (test_bit(IO_WQ_BIT_EXIT, &wq->state))
                        io_wq_cancel_tw_create(wq);
                io_worker_ref_put(wq);
                return true;
        }
        io_worker_ref_put(wq);
        clear_bit_unlock(0, &worker->create_state);
fail_release:
        io_worker_release(worker);
fail:
        atomic_dec(&acct->nr_running);
        io_worker_ref_put(wq);
        return false;
}

static void io_wq_dec_running(struct io_worker *worker)
{
        struct io_wq_acct *acct = io_wq_get_acct(worker);
        struct io_wq *wq = worker->wq;

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

        if (!atomic_dec_and_test(&acct->nr_running))
                return;
        if (!io_acct_run_queue(acct))
                return;

        raw_spin_unlock(&acct->lock);
        atomic_inc(&acct->nr_running);
        atomic_inc(&wq->worker_refs);
        io_queue_worker_create(worker, acct, create_worker_cb);
}

/*
 * 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_wq *wq, struct io_worker *worker)
{
        if (test_bit(IO_WORKER_F_FREE, &worker->flags)) {
                clear_bit(IO_WORKER_F_FREE, &worker->flags);
                raw_spin_lock(&wq->lock);
                hlist_nulls_del_init_rcu(&worker->nulls_node);
                raw_spin_unlock(&wq->lock);
        }
}

/*
 * No work, worker going to sleep. Move to freelist.
 */
static void __io_worker_idle(struct io_wq *wq, struct io_worker *worker)
        __must_hold(wq->lock)
{
        if (!test_bit(IO_WORKER_F_FREE, &worker->flags)) {
                set_bit(IO_WORKER_F_FREE, &worker->flags);
                hlist_nulls_add_head_rcu(&worker->nulls_node, &wq->free_list);
        }
}

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

static bool io_wait_on_hash(struct io_wq *wq, unsigned int hash)
{
        bool ret = false;

        spin_lock_irq(&wq->hash->wait.lock);
        if (list_empty(&wq->wait.entry)) {
                __add_wait_queue(&wq->hash->wait, &wq->wait);
                if (!test_bit(hash, &wq->hash->map)) {
                        __set_current_state(TASK_RUNNING);
                        list_del_init(&wq->wait.entry);
                        ret = true;
                }
        }
        spin_unlock_irq(&wq->hash->wait.lock);
        return ret;
}

static struct io_wq_work *io_get_next_work(struct io_wq_acct *acct,
                                           struct io_worker *worker)
        __must_hold(acct->lock)
{
        struct io_wq_work_node *node, *prev;
        struct io_wq_work *work, *tail;
        unsigned int stall_hash = -1U;
        struct io_wq *wq = worker->wq;

        wq_list_for_each(node, prev, &acct->work_list) {
                unsigned int hash;

                work = container_of(node, struct io_wq_work, list);

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

                hash = io_get_work_hash(work);
                /* all items with this hash lie in [work, tail] */
                tail = wq->hash_tail[hash];

                /* hashed, can run if not already running */
                if (!test_and_set_bit(hash, &wq->hash->map)) {
                        wq->hash_tail[hash] = NULL;
                        wq_list_cut(&acct->work_list, &tail->list, prev);
                        return work;
                }
                if (stall_hash == -1U)
                        stall_hash = hash;
                /* fast forward to a next hash, for-each will fix up @prev */
                node = &tail->list;
        }

        if (stall_hash != -1U) {
                bool unstalled;

                /*
                 * Set this before dropping the lock to avoid racing with new
                 * work being added and clearing the stalled bit.
                 */
                set_bit(IO_ACCT_STALLED_BIT, &acct->flags);
                raw_spin_unlock(&acct->lock);
                unstalled = io_wait_on_hash(wq, stall_hash);
                raw_spin_lock(&acct->lock);
                if (unstalled) {
                        clear_bit(IO_ACCT_STALLED_BIT, &acct->flags);
                        if (wq_has_sleeper(&wq->hash->wait))
                                wake_up(&wq->hash->wait);
                }
        }

        return NULL;
}

static void io_assign_current_work(struct io_worker *worker,
                                   struct io_wq_work *work)
{
        if (work) {
                io_run_task_work();
                cond_resched();
        }

        raw_spin_lock(&worker->lock);
        worker->cur_work = work;
        raw_spin_unlock(&worker->lock);
}

/*
 * Called with acct->lock held, drops it before returning
 */
static void io_worker_handle_work(struct io_wq_acct *acct,
                                  struct io_worker *worker)
        __releases(&acct->lock)
{
        struct io_wq *wq = worker->wq;
        bool do_kill = test_bit(IO_WQ_BIT_EXIT, &wq->state);

        do {
                struct io_wq_work *work;

                /*
                 * 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(acct, worker);
                if (work) {
                        /*
                         * Make sure cancelation can find this, even before
                         * it becomes the active work. That avoids a window
                         * where the work has been removed from our general
                         * work list, but isn't yet discoverable as the
                         * current work item for this worker.
                         */
                        raw_spin_lock(&worker->lock);
                        worker->cur_work = work;
                        raw_spin_unlock(&worker->lock);
                }

                raw_spin_unlock(&acct->lock);

                if (!work)
                        break;

                __io_worker_busy(wq, worker);

                io_assign_current_work(worker, work);
                __set_current_state(TASK_RUNNING);

                /* handle a whole dependent link */
                do {
                        struct io_wq_work *next_hashed, *linked;
                        unsigned int hash = io_get_work_hash(work);

                        next_hashed = wq_next_work(work);

                        if (do_kill &&
                            (atomic_read(&work->flags) & IO_WQ_WORK_UNBOUND))
                                atomic_or(IO_WQ_WORK_CANCEL, &work->flags);
                        wq->do_work(work);
                        io_assign_current_work(worker, NULL);

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

                        if (hash != -1U && !next_hashed) {
                                /* serialize hash clear with wake_up() */
                                spin_lock_irq(&wq->hash->wait.lock);
                                clear_bit(hash, &wq->hash->map);
                                clear_bit(IO_ACCT_STALLED_BIT, &acct->flags);
                                spin_unlock_irq(&wq->hash->wait.lock);
                                if (wq_has_sleeper(&wq->hash->wait))
                                        wake_up(&wq->hash->wait);
                        }
                } while (work);

                if (!__io_acct_run_queue(acct))
                        break;
                raw_spin_lock(&acct->lock);
        } while (1);
}

static int io_wq_worker(void *data)
{
        struct io_worker *worker = data;
        struct io_wq_acct *acct = io_wq_get_acct(worker);
        struct io_wq *wq = worker->wq;
        bool exit_mask = false, last_timeout = false;
        char buf[TASK_COMM_LEN];

        set_mask_bits(&worker->flags, 0,
                      BIT(IO_WORKER_F_UP) | BIT(IO_WORKER_F_RUNNING));

        snprintf(buf, sizeof(buf), "iou-wrk-%d", wq->task->pid);
        set_task_comm(current, buf);

        while (!test_bit(IO_WQ_BIT_EXIT, &wq->state)) {
                long ret;

                set_current_state(TASK_INTERRUPTIBLE);

                /*
                 * If we have work to do, io_acct_run_queue() returns with
                 * the acct->lock held. If not, it will drop it.
                 */
                while (io_acct_run_queue(acct))
                        io_worker_handle_work(acct, worker);

                raw_spin_lock(&wq->lock);
                /*
                 * Last sleep timed out. Exit if we're not the last worker,
                 * or if someone modified our affinity.
                 */
                if (last_timeout && (exit_mask || acct->nr_workers > 1)) {
                        acct->nr_workers--;
                        raw_spin_unlock(&wq->lock);
                        __set_current_state(TASK_RUNNING);
                        break;
                }
                last_timeout = false;
                __io_worker_idle(wq, worker);
                raw_spin_unlock(&wq->lock);
                if (io_run_task_work())
                        continue;
                ret = schedule_timeout(WORKER_IDLE_TIMEOUT);
                if (signal_pending(current)) {
                        struct ksignal ksig;

                        if (!get_signal(&ksig))
                                continue;
                        break;
                }
                if (!ret) {
                        last_timeout = true;
                        exit_mask = !cpumask_test_cpu(raw_smp_processor_id(),
                                                        wq->cpu_mask);
                }
        }

        if (test_bit(IO_WQ_BIT_EXIT, &wq->state) && io_acct_run_queue(acct))
                io_worker_handle_work(acct, worker);

        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 = tsk->worker_private;

        if (!worker)
                return;
        if (!test_bit(IO_WORKER_F_UP, &worker->flags))
                return;
        if (test_bit(IO_WORKER_F_RUNNING, &worker->flags))
                return;
        set_bit(IO_WORKER_F_RUNNING, &worker->flags);
        io_wq_inc_running(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 create a new one.
 */
void io_wq_worker_sleeping(struct task_struct *tsk)
{
        struct io_worker *worker = tsk->worker_private;

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

        clear_bit(IO_WORKER_F_RUNNING, &worker->flags);
        io_wq_dec_running(worker);
}

static void io_init_new_worker(struct io_wq *wq, struct io_worker *worker,
                               struct task_struct *tsk)
{
        tsk->worker_private = worker;
        worker->task = tsk;
        set_cpus_allowed_ptr(tsk, wq->cpu_mask);

        raw_spin_lock(&wq->lock);
        hlist_nulls_add_head_rcu(&worker->nulls_node, &wq->free_list);
        list_add_tail_rcu(&worker->all_list, &wq->all_list);
        set_bit(IO_WORKER_F_FREE, &worker->flags);
        raw_spin_unlock(&wq->lock);
        wake_up_new_task(tsk);
}

static bool io_wq_work_match_all(struct io_wq_work *work, void *data)
{
        return true;
}

static inline bool io_should_retry_thread(struct io_worker *worker, long err)
{
        /*
         * Prevent perpetual task_work retry, if the task (or its group) is
         * exiting.
         */
        if (fatal_signal_pending(current))
                return false;
        if (worker->init_retries++ >= WORKER_INIT_LIMIT)
                return false;

        switch (err) {
        case -EAGAIN:
        case -ERESTARTSYS:
        case -ERESTARTNOINTR:
        case -ERESTARTNOHAND:
                return true;
        default:
                return false;
        }
}

static void create_worker_cont(struct callback_head *cb)
{
        struct io_worker *worker;
        struct task_struct *tsk;
        struct io_wq *wq;

        worker = container_of(cb, struct io_worker, create_work);
        clear_bit_unlock(0, &worker->create_state);
        wq = worker->wq;
        tsk = create_io_thread(io_wq_worker, worker, NUMA_NO_NODE);
        if (!IS_ERR(tsk)) {
                io_init_new_worker(wq, worker, tsk);
                io_worker_release(worker);
                return;
        } else if (!io_should_retry_thread(worker, PTR_ERR(tsk))) {
                struct io_wq_acct *acct = io_wq_get_acct(worker);

                atomic_dec(&acct->nr_running);
                raw_spin_lock(&wq->lock);
                acct->nr_workers--;
                if (!acct->nr_workers) {
                        struct io_cb_cancel_data match = {
                                .fn             = io_wq_work_match_all,
                                .cancel_all     = true,
                        };

                        raw_spin_unlock(&wq->lock);
                        while (io_acct_cancel_pending_work(wq, acct, &match))
                                ;
                } else {
                        raw_spin_unlock(&wq->lock);
                }
                io_worker_ref_put(wq);
                kfree(worker);
                return;
        }

        /* re-create attempts grab a new worker ref, drop the existing one */
        io_worker_release(worker);
        schedule_work(&worker->work);
}

static void io_workqueue_create(struct work_struct *work)
{
        struct io_worker *worker = container_of(work, struct io_worker, work);
        struct io_wq_acct *acct = io_wq_get_acct(worker);

        if (!io_queue_worker_create(worker, acct, create_worker_cont))
                kfree(worker);
}

static bool create_io_worker(struct io_wq *wq, int index)
{
        struct io_wq_acct *acct = &wq->acct[index];
        struct io_worker *worker;
        struct task_struct *tsk;

        __set_current_state(TASK_RUNNING);

        worker = kzalloc(sizeof(*worker), GFP_KERNEL);
        if (!worker) {
fail:
                atomic_dec(&acct->nr_running);
                raw_spin_lock(&wq->lock);
                acct->nr_workers--;
                raw_spin_unlock(&wq->lock);
                io_worker_ref_put(wq);
                return false;
        }

        refcount_set(&worker->ref, 1);
        worker->wq = wq;
        raw_spin_lock_init(&worker->lock);
        init_completion(&worker->ref_done);

        if (index == IO_WQ_ACCT_BOUND)
                set_bit(IO_WORKER_F_BOUND, &worker->flags);

        tsk = create_io_thread(io_wq_worker, worker, NUMA_NO_NODE);
        if (!IS_ERR(tsk)) {
                io_init_new_worker(wq, worker, tsk);
        } else if (!io_should_retry_thread(worker, PTR_ERR(tsk))) {
                kfree(worker);
                goto fail;
        } else {
                INIT_WORK(&worker->work, io_workqueue_create);
                schedule_work(&worker->work);
        }

        return true;
}

/*
 * 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_wq *wq,
                                  bool (*func)(struct io_worker *, void *),
                                  void *data)
{
        struct io_worker *worker;
        bool ret = false;

        list_for_each_entry_rcu(worker, &wq->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;
}

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

static void io_run_cancel(struct io_wq_work *work, struct io_wq *wq)
{
        do {
                atomic_or(IO_WQ_WORK_CANCEL, &work->flags);
                wq->do_work(work);
                work = wq->free_work(work);
        } while (work);
}

static void io_wq_insert_work(struct io_wq *wq, struct io_wq_work *work)
{
        struct io_wq_acct *acct = io_work_get_acct(wq, work);
        unsigned int hash;
        struct io_wq_work *tail;

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

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

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

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

void io_wq_enqueue(struct io_wq *wq, struct io_wq_work *work)
{
        struct io_wq_acct *acct = io_work_get_acct(wq, work);
        unsigned int work_flags = atomic_read(&work->flags);
        struct io_cb_cancel_data match = {
                .fn             = io_wq_work_match_item,
                .data           = work,
                .cancel_all     = false,
        };
        bool do_create;

        /*
         * If io-wq is exiting for this task, or if the request has explicitly
         * been marked as one that should not get executed, cancel it here.
         */
        if (test_bit(IO_WQ_BIT_EXIT, &wq->state) ||
            (work_flags & IO_WQ_WORK_CANCEL)) {
                io_run_cancel(work, wq);
                return;
        }

        raw_spin_lock(&acct->lock);
        io_wq_insert_work(wq, work);
        clear_bit(IO_ACCT_STALLED_BIT, &acct->flags);
        raw_spin_unlock(&acct->lock);

        rcu_read_lock();
        do_create = !io_wq_activate_free_worker(wq, acct);
        rcu_read_unlock();

        if (do_create && ((work_flags & IO_WQ_WORK_CONCURRENT) ||
            !atomic_read(&acct->nr_running))) {
                bool did_create;

                did_create = io_wq_create_worker(wq, acct);
                if (likely(did_create))
                        return;

                raw_spin_lock(&wq->lock);
                if (acct->nr_workers) {
                        raw_spin_unlock(&wq->lock);
                        return;
                }
                raw_spin_unlock(&wq->lock);

                /* fatal condition, failed to create the first worker */
                io_acct_cancel_pending_work(wq, acct, &match);
        }
}

/*
 * 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);
        atomic_or(IO_WQ_WORK_HASHED | (bit << IO_WQ_HASH_SHIFT), &work->flags);
}

static bool __io_wq_worker_cancel(struct io_worker *worker,
                                  struct io_cb_cancel_data *match,
                                  struct io_wq_work *work)
{
        if (work && match->fn(work, match->data)) {
                atomic_or(IO_WQ_WORK_CANCEL, &work->flags);
                __set_notify_signal(worker->task);
                return true;
        }

        return false;
}

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

        /*
         * Hold the lock to avoid ->cur_work going out of scope, caller
         * may dereference the passed in work.
         */
        raw_spin_lock(&worker->lock);
        if (__io_wq_worker_cancel(worker, match, worker->cur_work))
                match->nr_running++;
        raw_spin_unlock(&worker->lock);

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

static inline void io_wq_remove_pending(struct io_wq *wq,
                                         struct io_wq_work *work,
                                         struct io_wq_work_node *prev)
{
        struct io_wq_acct *acct = io_work_get_acct(wq, work);
        unsigned int hash = io_get_work_hash(work);
        struct io_wq_work *prev_work = NULL;

        if (io_wq_is_hashed(work) && work == wq->hash_tail[hash]) {
                if (prev)
                        prev_work = container_of(prev, struct io_wq_work, list);
                if (prev_work && io_get_work_hash(prev_work) == hash)
                        wq->hash_tail[hash] = prev_work;
                else
                        wq->hash_tail[hash] = NULL;
        }
        wq_list_del(&acct->work_list, &work->list, prev);
}

static bool io_acct_cancel_pending_work(struct io_wq *wq,
                                        struct io_wq_acct *acct,
                                        struct io_cb_cancel_data *match)
{
        struct io_wq_work_node *node, *prev;
        struct io_wq_work *work;

        raw_spin_lock(&acct->lock);
        wq_list_for_each(node, prev, &acct->work_list) {
                work = container_of(node, struct io_wq_work, list);
                if (!match->fn(work, match->data))
                        continue;
                io_wq_remove_pending(wq, work, prev);
                raw_spin_unlock(&acct->lock);
                io_run_cancel(work, wq);
                match->nr_pending++;
                /* not safe to continue after unlock */
                return true;
        }
        raw_spin_unlock(&acct->lock);

        return false;
}

static void io_wq_cancel_pending_work(struct io_wq *wq,
                                      struct io_cb_cancel_data *match)
{
        int i;
retry:
        for (i = 0; i < IO_WQ_ACCT_NR; i++) {
                struct io_wq_acct *acct = io_get_acct(wq, i == 0);

                if (io_acct_cancel_pending_work(wq, acct, match)) {
                        if (match->cancel_all)
                                goto retry;
                        break;
                }
        }
}

static void io_wq_cancel_running_work(struct io_wq *wq,
                                       struct io_cb_cancel_data *match)
{
        rcu_read_lock();
        io_wq_for_each_worker(wq, 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,
        };

        /*
         * 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.
         *
         * Then 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.
         *
         * Do both of these while holding the wq->lock, to ensure that
         * we'll find a work item regardless of state.
         */
        io_wq_cancel_pending_work(wq, &match);
        if (match.nr_pending && !match.cancel_all)
                return IO_WQ_CANCEL_OK;

        raw_spin_lock(&wq->lock);
        io_wq_cancel_running_work(wq, &match);
        raw_spin_unlock(&wq->lock);
        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 int io_wq_hash_wake(struct wait_queue_entry *wait, unsigned mode,
                            int sync, void *key)
{
        struct io_wq *wq = container_of(wait, struct io_wq, wait);
        int i;

        list_del_init(&wait->entry);

        rcu_read_lock();
        for (i = 0; i < IO_WQ_ACCT_NR; i++) {
                struct io_wq_acct *acct = &wq->acct[i];

                if (test_and_clear_bit(IO_ACCT_STALLED_BIT, &acct->flags))
                        io_wq_activate_free_worker(wq, acct);
        }
        rcu_read_unlock();
        return 1;
}

struct io_wq *io_wq_create(unsigned bounded, struct io_wq_data *data)
{
        int ret, i;
        struct io_wq *wq;

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

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

        refcount_inc(&data->hash->refs);
        wq->hash = data->hash;
        wq->free_work = data->free_work;
        wq->do_work = data->do_work;

        ret = -ENOMEM;

        if (!alloc_cpumask_var(&wq->cpu_mask, GFP_KERNEL))
                goto err;
        cpuset_cpus_allowed(data->task, wq->cpu_mask);
        wq->acct[IO_WQ_ACCT_BOUND].max_workers = bounded;
        wq->acct[IO_WQ_ACCT_UNBOUND].max_workers =
                                task_rlimit(current, RLIMIT_NPROC);
        INIT_LIST_HEAD(&wq->wait.entry);
        wq->wait.func = io_wq_hash_wake;
        for (i = 0; i < IO_WQ_ACCT_NR; i++) {
                struct io_wq_acct *acct = &wq->acct[i];

                acct->index = i;
                atomic_set(&acct->nr_running, 0);
                INIT_WQ_LIST(&acct->work_list);
                raw_spin_lock_init(&acct->lock);
        }

        raw_spin_lock_init(&wq->lock);
        INIT_HLIST_NULLS_HEAD(&wq->free_list, 0);
        INIT_LIST_HEAD(&wq->all_list);

        wq->task = get_task_struct(data->task);
        atomic_set(&wq->worker_refs, 1);
        init_completion(&wq->worker_done);
        ret = cpuhp_state_add_instance_nocalls(io_wq_online, &wq->cpuhp_node);
        if (ret)
                goto err;

        return wq;
err:
        io_wq_put_hash(data->hash);
        free_cpumask_var(wq->cpu_mask);
        kfree(wq);
        return ERR_PTR(ret);
}

static bool io_task_work_match(struct callback_head *cb, void *data)
{
        struct io_worker *worker;

        if (cb->func != create_worker_cb && cb->func != create_worker_cont)
                return false;
        worker = container_of(cb, struct io_worker, create_work);
        return worker->wq == data;
}

void io_wq_exit_start(struct io_wq *wq)
{
        set_bit(IO_WQ_BIT_EXIT, &wq->state);
}

static void io_wq_cancel_tw_create(struct io_wq *wq)
{
        struct callback_head *cb;

        while ((cb = task_work_cancel_match(wq->task, io_task_work_match, wq)) != NULL) {
                struct io_worker *worker;

                worker = container_of(cb, struct io_worker, create_work);
                io_worker_cancel_cb(worker);
                /*
                 * Only the worker continuation helper has worker allocated and
                 * hence needs freeing.
                 */
                if (cb->func == create_worker_cont)
                        kfree(worker);
        }
}

static void io_wq_exit_workers(struct io_wq *wq)
{
        if (!wq->task)
                return;

        io_wq_cancel_tw_create(wq);

        rcu_read_lock();
        io_wq_for_each_worker(wq, io_wq_worker_wake, NULL);
        rcu_read_unlock();
        io_worker_ref_put(wq);
        wait_for_completion(&wq->worker_done);

        spin_lock_irq(&wq->hash->wait.lock);
        list_del_init(&wq->wait.entry);
        spin_unlock_irq(&wq->hash->wait.lock);

        put_task_struct(wq->task);
        wq->task = NULL;
}

static void io_wq_destroy(struct io_wq *wq)
{
        struct io_cb_cancel_data match = {
                .fn             = io_wq_work_match_all,
                .cancel_all     = true,
        };

        cpuhp_state_remove_instance_nocalls(io_wq_online, &wq->cpuhp_node);
        io_wq_cancel_pending_work(wq, &match);
        free_cpumask_var(wq->cpu_mask);
        io_wq_put_hash(wq->hash);
        kfree(wq);
}

void io_wq_put_and_exit(struct io_wq *wq)
{
        WARN_ON_ONCE(!test_bit(IO_WQ_BIT_EXIT, &wq->state));

        io_wq_exit_workers(wq);
        io_wq_destroy(wq);
}

struct online_data {
        unsigned int cpu;
        bool online;
};

static bool io_wq_worker_affinity(struct io_worker *worker, void *data)
{
        struct online_data *od = data;

        if (od->online)
                cpumask_set_cpu(od->cpu, worker->wq->cpu_mask);
        else
                cpumask_clear_cpu(od->cpu, worker->wq->cpu_mask);
        return false;
}

static int __io_wq_cpu_online(struct io_wq *wq, unsigned int cpu, bool online)
{
        struct online_data od = {
                .cpu = cpu,
                .online = online
        };

        rcu_read_lock();
        io_wq_for_each_worker(wq, io_wq_worker_affinity, &od);
        rcu_read_unlock();
        return 0;
}

static int io_wq_cpu_online(unsigned int cpu, struct hlist_node *node)
{
        struct io_wq *wq = hlist_entry_safe(node, struct io_wq, cpuhp_node);

        return __io_wq_cpu_online(wq, cpu, true);
}

static int io_wq_cpu_offline(unsigned int cpu, struct hlist_node *node)
{
        struct io_wq *wq = hlist_entry_safe(node, struct io_wq, cpuhp_node);

        return __io_wq_cpu_online(wq, cpu, false);
}

int io_wq_cpu_affinity(struct io_uring_task *tctx, cpumask_var_t mask)
{
        cpumask_var_t allowed_mask;
        int ret = 0;

        if (!tctx || !tctx->io_wq)
                return -EINVAL;

        if (!alloc_cpumask_var(&allowed_mask, GFP_KERNEL))
                return -ENOMEM;

        rcu_read_lock();
        cpuset_cpus_allowed(tctx->io_wq->task, allowed_mask);
        if (mask) {
                if (cpumask_subset(mask, allowed_mask))
                        cpumask_copy(tctx->io_wq->cpu_mask, mask);
                else
                        ret = -EINVAL;
        } else {
                cpumask_copy(tctx->io_wq->cpu_mask, allowed_mask);
        }
        rcu_read_unlock();

        free_cpumask_var(allowed_mask);
        return ret;
}

/*
 * Set max number of unbounded workers, returns old value. If new_count is 0,
 * then just return the old value.
 */
int io_wq_max_workers(struct io_wq *wq, int *new_count)
{
        struct io_wq_acct *acct;
        int prev[IO_WQ_ACCT_NR];
        int i;

        BUILD_BUG_ON((int) IO_WQ_ACCT_BOUND   != (int) IO_WQ_BOUND);
        BUILD_BUG_ON((int) IO_WQ_ACCT_UNBOUND != (int) IO_WQ_UNBOUND);
        BUILD_BUG_ON((int) IO_WQ_ACCT_NR      != 2);

        for (i = 0; i < IO_WQ_ACCT_NR; i++) {
                if (new_count[i] > task_rlimit(current, RLIMIT_NPROC))
                        new_count[i] = task_rlimit(current, RLIMIT_NPROC);
        }

        for (i = 0; i < IO_WQ_ACCT_NR; i++)
                prev[i] = 0;

        rcu_read_lock();

        raw_spin_lock(&wq->lock);
        for (i = 0; i < IO_WQ_ACCT_NR; i++) {
                acct = &wq->acct[i];
                prev[i] = max_t(int, acct->max_workers, prev[i]);
                if (new_count[i])
                        acct->max_workers = new_count[i];
        }
        raw_spin_unlock(&wq->lock);
        rcu_read_unlock();

        for (i = 0; i < IO_WQ_ACCT_NR; i++)
                new_count[i] = prev[i];

        return 0;
}

static __init int io_wq_init(void)
{
        int ret;

        ret = cpuhp_setup_state_multi(CPUHP_AP_ONLINE_DYN, "io-wq/online",
                                        io_wq_cpu_online, io_wq_cpu_offline);
        if (ret < 0)
                return ret;
        io_wq_online = ret;
        return 0;
}
subsys_initcall(io_wq_init);