// SPDX-License-Identifier: GPL-2.0
/*
 * Functions related to io context handling
 */
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/bio.h>
#include <linux/blkdev.h>
#include <linux/slab.h>
#include <linux/security.h>
#include <linux/sched/task.h>

#include "blk.h"
#include "blk-mq-sched.h"

/*
 * For io context allocations
 */
static struct kmem_cache *iocontext_cachep;

#ifdef CONFIG_BLK_ICQ
/**
 * get_io_context - increment reference count to io_context
 * @ioc: io_context to get
 *
 * Increment reference count to @ioc.
 */
static void get_io_context(struct io_context *ioc)
{
        BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
        atomic_long_inc(&ioc->refcount);
}

static void icq_free_icq_rcu(struct rcu_head *head)
{
        struct io_cq *icq = container_of(head, struct io_cq, __rcu_head);

        kmem_cache_free(icq->__rcu_icq_cache, icq);
}

/*
 * Exit an icq. Called with ioc locked for blk-mq, and with both ioc
 * and queue locked for legacy.
 */
static void ioc_exit_icq(struct io_cq *icq)
{
        struct elevator_type *et = icq->q->elevator->type;

        if (icq->flags & ICQ_EXITED)
                return;

        if (et->ops.exit_icq)
                et->ops.exit_icq(icq);

        icq->flags |= ICQ_EXITED;
}

static void ioc_exit_icqs(struct io_context *ioc)
{
        struct io_cq *icq;

        spin_lock_irq(&ioc->lock);
        hlist_for_each_entry(icq, &ioc->icq_list, ioc_node)
                ioc_exit_icq(icq);
        spin_unlock_irq(&ioc->lock);
}

/*
 * Release an icq. Called with ioc locked for blk-mq, and with both ioc
 * and queue locked for legacy.
 */
static void ioc_destroy_icq(struct io_cq *icq)
{
        struct io_context *ioc = icq->ioc;
        struct request_queue *q = icq->q;
        struct elevator_type *et = q->elevator->type;

        lockdep_assert_held(&ioc->lock);
        lockdep_assert_held(&q->queue_lock);

        if (icq->flags & ICQ_DESTROYED)
                return;

        radix_tree_delete(&ioc->icq_tree, icq->q->id);
        hlist_del_init(&icq->ioc_node);
        list_del_init(&icq->q_node);

        /*
         * Both setting lookup hint to and clearing it from @icq are done
         * under queue_lock.  If it's not pointing to @icq now, it never
         * will.  Hint assignment itself can race safely.
         */
        if (rcu_access_pointer(ioc->icq_hint) == icq)
                rcu_assign_pointer(ioc->icq_hint, NULL);

        ioc_exit_icq(icq);

        /*
         * @icq->q might have gone away by the time RCU callback runs
         * making it impossible to determine icq_cache.  Record it in @icq.
         */
        icq->__rcu_icq_cache = et->icq_cache;
        icq->flags |= ICQ_DESTROYED;
        call_rcu(&icq->__rcu_head, icq_free_icq_rcu);
}

/*
 * Slow path for ioc release in put_io_context().  Performs double-lock
 * dancing to unlink all icq's and then frees ioc.
 */
static void ioc_release_fn(struct work_struct *work)
{
        struct io_context *ioc = container_of(work, struct io_context,
                                              release_work);
        spin_lock_irq(&ioc->lock);

        while (!hlist_empty(&ioc->icq_list)) {
                struct io_cq *icq = hlist_entry(ioc->icq_list.first,
                                                struct io_cq, ioc_node);
                struct request_queue *q = icq->q;

                if (spin_trylock(&q->queue_lock)) {
                        ioc_destroy_icq(icq);
                        spin_unlock(&q->queue_lock);
                } else {
                        /* Make sure q and icq cannot be freed. */
                        rcu_read_lock();

                        /* Re-acquire the locks in the correct order. */
                        spin_unlock(&ioc->lock);
                        spin_lock(&q->queue_lock);
                        spin_lock(&ioc->lock);

                        ioc_destroy_icq(icq);

                        spin_unlock(&q->queue_lock);
                        rcu_read_unlock();
                }
        }

        spin_unlock_irq(&ioc->lock);

        kmem_cache_free(iocontext_cachep, ioc);
}

/*
 * Releasing icqs requires reverse order double locking and we may already be
 * holding a queue_lock.  Do it asynchronously from a workqueue.
 */
static bool ioc_delay_free(struct io_context *ioc)
{
        unsigned long flags;

        spin_lock_irqsave(&ioc->lock, flags);
        if (!hlist_empty(&ioc->icq_list)) {
                queue_work(system_power_efficient_wq, &ioc->release_work);
                spin_unlock_irqrestore(&ioc->lock, flags);
                return true;
        }
        spin_unlock_irqrestore(&ioc->lock, flags);
        return false;
}

/**
 * ioc_clear_queue - break any ioc association with the specified queue
 * @q: request_queue being cleared
 *
 * Walk @q->icq_list and exit all io_cq's.
 */
void ioc_clear_queue(struct request_queue *q)
{
        spin_lock_irq(&q->queue_lock);
        while (!list_empty(&q->icq_list)) {
                struct io_cq *icq =
                        list_first_entry(&q->icq_list, struct io_cq, q_node);

                /*
                 * Other context won't hold ioc lock to wait for queue_lock, see
                 * details in ioc_release_fn().
                 */
                spin_lock(&icq->ioc->lock);
                ioc_destroy_icq(icq);
                spin_unlock(&icq->ioc->lock);
        }
        spin_unlock_irq(&q->queue_lock);
}
#else /* CONFIG_BLK_ICQ */
static inline void ioc_exit_icqs(struct io_context *ioc)
{
}
static inline bool ioc_delay_free(struct io_context *ioc)
{
        return false;
}
#endif /* CONFIG_BLK_ICQ */

/**
 * put_io_context - put a reference of io_context
 * @ioc: io_context to put
 *
 * Decrement reference count of @ioc and release it if the count reaches
 * zero.
 */
void put_io_context(struct io_context *ioc)
{
        BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
        if (atomic_long_dec_and_test(&ioc->refcount) && !ioc_delay_free(ioc))
                kmem_cache_free(iocontext_cachep, ioc);
}
EXPORT_SYMBOL_GPL(put_io_context);

/* Called by the exiting task */
void exit_io_context(struct task_struct *task)
{
        struct io_context *ioc;

        task_lock(task);
        ioc = task->io_context;
        task->io_context = NULL;
        task_unlock(task);

        if (atomic_dec_and_test(&ioc->active_ref)) {
                ioc_exit_icqs(ioc);
                put_io_context(ioc);
        }
}

static struct io_context *alloc_io_context(gfp_t gfp_flags, int node)
{
        struct io_context *ioc;

        ioc = kmem_cache_alloc_node(iocontext_cachep, gfp_flags | __GFP_ZERO,
                                    node);
        if (unlikely(!ioc))
                return NULL;

        atomic_long_set(&ioc->refcount, 1);
        atomic_set(&ioc->active_ref, 1);
#ifdef CONFIG_BLK_ICQ
        spin_lock_init(&ioc->lock);
        INIT_RADIX_TREE(&ioc->icq_tree, GFP_ATOMIC);
        INIT_HLIST_HEAD(&ioc->icq_list);
        INIT_WORK(&ioc->release_work, ioc_release_fn);
#endif
        ioc->ioprio = IOPRIO_DEFAULT;

        return ioc;
}

int set_task_ioprio(struct task_struct *task, int ioprio)
{
        int err;
        const struct cred *cred = current_cred(), *tcred;

        rcu_read_lock();
        tcred = __task_cred(task);
        if (!uid_eq(tcred->uid, cred->euid) &&
            !uid_eq(tcred->uid, cred->uid) && !capable(CAP_SYS_NICE)) {
                rcu_read_unlock();
                return -EPERM;
        }
        rcu_read_unlock();

        err = security_task_setioprio(task, ioprio);
        if (err)
                return err;

        task_lock(task);
        if (unlikely(!task->io_context)) {
                struct io_context *ioc;

                task_unlock(task);

                ioc = alloc_io_context(GFP_ATOMIC, NUMA_NO_NODE);
                if (!ioc)
                        return -ENOMEM;

                task_lock(task);
                if (task->flags & PF_EXITING) {
                        kmem_cache_free(iocontext_cachep, ioc);
                        goto out;
                }
                if (task->io_context)
                        kmem_cache_free(iocontext_cachep, ioc);
                else
                        task->io_context = ioc;
        }
        task->io_context->ioprio = ioprio;
out:
        task_unlock(task);
        return 0;
}
EXPORT_SYMBOL_GPL(set_task_ioprio);

int __copy_io(unsigned long clone_flags, struct task_struct *tsk)
{
        struct io_context *ioc = current->io_context;

        /*
         * Share io context with parent, if CLONE_IO is set
         */
        if (clone_flags & CLONE_IO) {
                atomic_inc(&ioc->active_ref);
                tsk->io_context = ioc;
        } else if (ioprio_valid(ioc->ioprio)) {
                tsk->io_context = alloc_io_context(GFP_KERNEL, NUMA_NO_NODE);
                if (!tsk->io_context)
                        return -ENOMEM;
                tsk->io_context->ioprio = ioc->ioprio;
        }

        return 0;
}

#ifdef CONFIG_BLK_ICQ
/**
 * ioc_lookup_icq - lookup io_cq from ioc
 * @q: the associated request_queue
 *
 * Look up io_cq associated with @ioc - @q pair from @ioc.  Must be called
 * with @q->queue_lock held.
 */
struct io_cq *ioc_lookup_icq(struct request_queue *q)
{
        struct io_context *ioc = current->io_context;
        struct io_cq *icq;

        lockdep_assert_held(&q->queue_lock);

        /*
         * icq's are indexed from @ioc using radix tree and hint pointer,
         * both of which are protected with RCU.  All removals are done
         * holding both q and ioc locks, and we're holding q lock - if we
         * find a icq which points to us, it's guaranteed to be valid.
         */
        rcu_read_lock();
        icq = rcu_dereference(ioc->icq_hint);
        if (icq && icq->q == q)
                goto out;

        icq = radix_tree_lookup(&ioc->icq_tree, q->id);
        if (icq && icq->q == q)
                rcu_assign_pointer(ioc->icq_hint, icq); /* allowed to race */
        else
                icq = NULL;
out:
        rcu_read_unlock();
        return icq;
}
EXPORT_SYMBOL(ioc_lookup_icq);

/**
 * ioc_create_icq - create and link io_cq
 * @q: request_queue of interest
 *
 * Make sure io_cq linking @ioc and @q exists.  If icq doesn't exist, they
 * will be created using @gfp_mask.
 *
 * The caller is responsible for ensuring @ioc won't go away and @q is
 * alive and will stay alive until this function returns.
 */
static struct io_cq *ioc_create_icq(struct request_queue *q)
{
        struct io_context *ioc = current->io_context;
        struct elevator_type *et = q->elevator->type;
        struct io_cq *icq;

        /* allocate stuff */
        icq = kmem_cache_alloc_node(et->icq_cache, GFP_ATOMIC | __GFP_ZERO,
                                    q->node);
        if (!icq)
                return NULL;

        if (radix_tree_maybe_preload(GFP_ATOMIC) < 0) {
                kmem_cache_free(et->icq_cache, icq);
                return NULL;
        }

        icq->ioc = ioc;
        icq->q = q;
        INIT_LIST_HEAD(&icq->q_node);
        INIT_HLIST_NODE(&icq->ioc_node);

        /* lock both q and ioc and try to link @icq */
        spin_lock_irq(&q->queue_lock);
        spin_lock(&ioc->lock);

        if (likely(!radix_tree_insert(&ioc->icq_tree, q->id, icq))) {
                hlist_add_head(&icq->ioc_node, &ioc->icq_list);
                list_add(&icq->q_node, &q->icq_list);
                if (et->ops.init_icq)
                        et->ops.init_icq(icq);
        } else {
                kmem_cache_free(et->icq_cache, icq);
                icq = ioc_lookup_icq(q);
                if (!icq)
                        printk(KERN_ERR "cfq: icq link failed!\n");
        }

        spin_unlock(&ioc->lock);
        spin_unlock_irq(&q->queue_lock);
        radix_tree_preload_end();
        return icq;
}

struct io_cq *ioc_find_get_icq(struct request_queue *q)
{
        struct io_context *ioc = current->io_context;
        struct io_cq *icq = NULL;

        if (unlikely(!ioc)) {
                ioc = alloc_io_context(GFP_ATOMIC, q->node);
                if (!ioc)
                        return NULL;

                task_lock(current);
                if (current->io_context) {
                        kmem_cache_free(iocontext_cachep, ioc);
                        ioc = current->io_context;
                } else {
                        current->io_context = ioc;
                }

                get_io_context(ioc);
                task_unlock(current);
        } else {
                get_io_context(ioc);

                spin_lock_irq(&q->queue_lock);
                icq = ioc_lookup_icq(q);
                spin_unlock_irq(&q->queue_lock);
        }

        if (!icq) {
                icq = ioc_create_icq(q);
                if (!icq) {
                        put_io_context(ioc);
                        return NULL;
                }
        }
        return icq;
}
EXPORT_SYMBOL_GPL(ioc_find_get_icq);
#endif /* CONFIG_BLK_ICQ */

static int __init blk_ioc_init(void)
{
        iocontext_cachep = kmem_cache_create("blkdev_ioc",
                        sizeof(struct io_context), 0, SLAB_PANIC, NULL);
        return 0;
}
subsys_initcall(blk_ioc_init);