btrfs: fix memory ordering between normal and ordered work functions

[mirror_ubuntu-jammy-kernel.git] / fs / aio.c

/*
 *      An async IO implementation for Linux
 *      Written by Benjamin LaHaise <bcrl@kvack.org>
 *
 *      Implements an efficient asynchronous io interface.
 *
 *      Copyright 2000, 2001, 2002 Red Hat, Inc.  All Rights Reserved.
 *      Copyright 2018 Christoph Hellwig.
 *
 *      See ../COPYING for licensing terms.
 */
#define pr_fmt(fmt) "%s: " fmt, __func__

#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/errno.h>
#include <linux/time.h>
#include <linux/aio_abi.h>
#include <linux/export.h>
#include <linux/syscalls.h>
#include <linux/backing-dev.h>
#include <linux/refcount.h>
#include <linux/uio.h>

#include <linux/sched/signal.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/mm.h>
#include <linux/mman.h>
#include <linux/percpu.h>
#include <linux/slab.h>
#include <linux/timer.h>
#include <linux/aio.h>
#include <linux/highmem.h>
#include <linux/workqueue.h>
#include <linux/security.h>
#include <linux/eventfd.h>
#include <linux/blkdev.h>
#include <linux/compat.h>
#include <linux/migrate.h>
#include <linux/ramfs.h>
#include <linux/percpu-refcount.h>
#include <linux/mount.h>
#include <linux/pseudo_fs.h>

#include <linux/uaccess.h>
#include <linux/nospec.h>

#include "internal.h"

#define KIOCB_KEY               0

#define AIO_RING_MAGIC                  0xa10a10a1
#define AIO_RING_COMPAT_FEATURES        1
#define AIO_RING_INCOMPAT_FEATURES      0
struct aio_ring {
        unsigned        id;     /* kernel internal index number */
        unsigned        nr;     /* number of io_events */
        unsigned        head;   /* Written to by userland or under ring_lock
                                 * mutex by aio_read_events_ring(). */
        unsigned        tail;

        unsigned        magic;
        unsigned        compat_features;
        unsigned        incompat_features;
        unsigned        header_length;  /* size of aio_ring */


        struct io_event         io_events[];
}; /* 128 bytes + ring size */

/*
 * Plugging is meant to work with larger batches of IOs. If we don't
 * have more than the below, then don't bother setting up a plug.
 */
#define AIO_PLUG_THRESHOLD      2

#define AIO_RING_PAGES  8

struct kioctx_table {
        struct rcu_head         rcu;
        unsigned                nr;
        struct kioctx __rcu     *table[];
};

struct kioctx_cpu {
        unsigned                reqs_available;
};

struct ctx_rq_wait {
        struct completion comp;
        atomic_t count;
};

struct kioctx {
        struct percpu_ref       users;
        atomic_t                dead;

        struct percpu_ref       reqs;

        unsigned long           user_id;

        struct __percpu kioctx_cpu *cpu;

        /*
         * For percpu reqs_available, number of slots we move to/from global
         * counter at a time:
         */
        unsigned                req_batch;
        /*
         * This is what userspace passed to io_setup(), it's not used for
         * anything but counting against the global max_reqs quota.
         *
         * The real limit is nr_events - 1, which will be larger (see
         * aio_setup_ring())
         */
        unsigned                max_reqs;

        /* Size of ringbuffer, in units of struct io_event */
        unsigned                nr_events;

        unsigned long           mmap_base;
        unsigned long           mmap_size;

        struct page             **ring_pages;
        long                    nr_pages;

        struct rcu_work         free_rwork;     /* see free_ioctx() */

        /*
         * signals when all in-flight requests are done
         */
        struct ctx_rq_wait      *rq_wait;

        struct {
                /*
                 * This counts the number of available slots in the ringbuffer,
                 * so we avoid overflowing it: it's decremented (if positive)
                 * when allocating a kiocb and incremented when the resulting
                 * io_event is pulled off the ringbuffer.
                 *
                 * We batch accesses to it with a percpu version.
                 */
                atomic_t        reqs_available;
        } ____cacheline_aligned_in_smp;

        struct {
                spinlock_t      ctx_lock;
                struct list_head active_reqs;   /* used for cancellation */
        } ____cacheline_aligned_in_smp;

        struct {
                struct mutex    ring_lock;
                wait_queue_head_t wait;
        } ____cacheline_aligned_in_smp;

        struct {
                unsigned        tail;
                unsigned        completed_events;
                spinlock_t      completion_lock;
        } ____cacheline_aligned_in_smp;

        struct page             *internal_pages[AIO_RING_PAGES];
        struct file             *aio_ring_file;

        unsigned                id;
};

/*
 * First field must be the file pointer in all the
 * iocb unions! See also 'struct kiocb' in <linux/fs.h>
 */
struct fsync_iocb {
        struct file             *file;
        struct work_struct      work;
        bool                    datasync;
        struct cred             *creds;
};

struct poll_iocb {
        struct file             *file;
        struct wait_queue_head  *head;
        __poll_t                events;
        bool                    done;
        bool                    cancelled;
        struct wait_queue_entry wait;
        struct work_struct      work;
};

/*
 * NOTE! Each of the iocb union members has the file pointer
 * as the first entry in their struct definition. So you can
 * access the file pointer through any of the sub-structs,
 * or directly as just 'ki_filp' in this struct.
 */
struct aio_kiocb {
        union {
                struct file             *ki_filp;
                struct kiocb            rw;
                struct fsync_iocb       fsync;
                struct poll_iocb        poll;
        };

        struct kioctx           *ki_ctx;
        kiocb_cancel_fn         *ki_cancel;

        struct io_event         ki_res;

        struct list_head        ki_list;        /* the aio core uses this
                                                 * for cancellation */
        refcount_t              ki_refcnt;

        /*
         * If the aio_resfd field of the userspace iocb is not zero,
         * this is the underlying eventfd context to deliver events to.
         */
        struct eventfd_ctx      *ki_eventfd;
};

/*------ sysctl variables----*/
static DEFINE_SPINLOCK(aio_nr_lock);
unsigned long aio_nr;           /* current system wide number of aio requests */
unsigned long aio_max_nr = 0x10000; /* system wide maximum number of aio requests */
/*----end sysctl variables---*/

static struct kmem_cache        *kiocb_cachep;
static struct kmem_cache        *kioctx_cachep;

static struct vfsmount *aio_mnt;

static const struct file_operations aio_ring_fops;
static const struct address_space_operations aio_ctx_aops;

static struct file *aio_private_file(struct kioctx *ctx, loff_t nr_pages)
{
        struct file *file;
        struct inode *inode = alloc_anon_inode(aio_mnt->mnt_sb);
        if (IS_ERR(inode))
                return ERR_CAST(inode);

        inode->i_mapping->a_ops = &aio_ctx_aops;
        inode->i_mapping->private_data = ctx;
        inode->i_size = PAGE_SIZE * nr_pages;

        file = alloc_file_pseudo(inode, aio_mnt, "[aio]",
                                O_RDWR, &aio_ring_fops);
        if (IS_ERR(file))
                iput(inode);
        return file;
}

static int aio_init_fs_context(struct fs_context *fc)
{
        if (!init_pseudo(fc, AIO_RING_MAGIC))
                return -ENOMEM;
        fc->s_iflags |= SB_I_NOEXEC;
        return 0;
}

/* aio_setup
 *      Creates the slab caches used by the aio routines, panic on
 *      failure as this is done early during the boot sequence.
 */
static int __init aio_setup(void)
{
        static struct file_system_type aio_fs = {
                .name           = "aio",
                .init_fs_context = aio_init_fs_context,
                .kill_sb        = kill_anon_super,
        };
        aio_mnt = kern_mount(&aio_fs);
        if (IS_ERR(aio_mnt))
                panic("Failed to create aio fs mount.");

        kiocb_cachep = KMEM_CACHE(aio_kiocb, SLAB_HWCACHE_ALIGN|SLAB_PANIC);
        kioctx_cachep = KMEM_CACHE(kioctx,SLAB_HWCACHE_ALIGN|SLAB_PANIC);
        return 0;
}
__initcall(aio_setup);

static void put_aio_ring_file(struct kioctx *ctx)
{
        struct file *aio_ring_file = ctx->aio_ring_file;
        struct address_space *i_mapping;

        if (aio_ring_file) {
                truncate_setsize(file_inode(aio_ring_file), 0);

                /* Prevent further access to the kioctx from migratepages */
                i_mapping = aio_ring_file->f_mapping;
                spin_lock(&i_mapping->private_lock);
                i_mapping->private_data = NULL;
                ctx->aio_ring_file = NULL;
                spin_unlock(&i_mapping->private_lock);

                fput(aio_ring_file);
        }
}

static void aio_free_ring(struct kioctx *ctx)
{
        int i;

        /* Disconnect the kiotx from the ring file.  This prevents future
         * accesses to the kioctx from page migration.
         */
        put_aio_ring_file(ctx);

        for (i = 0; i < ctx->nr_pages; i++) {
                struct page *page;
                pr_debug("pid(%d) [%d] page->count=%d\n", current->pid, i,
                                page_count(ctx->ring_pages[i]));
                page = ctx->ring_pages[i];
                if (!page)
                        continue;
                ctx->ring_pages[i] = NULL;
                put_page(page);
        }

        if (ctx->ring_pages && ctx->ring_pages != ctx->internal_pages) {
                kfree(ctx->ring_pages);
                ctx->ring_pages = NULL;
        }
}

static int aio_ring_mremap(struct vm_area_struct *vma)
{
        struct file *file = vma->vm_file;
        struct mm_struct *mm = vma->vm_mm;
        struct kioctx_table *table;
        int i, res = -EINVAL;

        spin_lock(&mm->ioctx_lock);
        rcu_read_lock();
        table = rcu_dereference(mm->ioctx_table);
        for (i = 0; i < table->nr; i++) {
                struct kioctx *ctx;

                ctx = rcu_dereference(table->table[i]);
                if (ctx && ctx->aio_ring_file == file) {
                        if (!atomic_read(&ctx->dead)) {
                                ctx->user_id = ctx->mmap_base = vma->vm_start;
                                res = 0;
                        }
                        break;
                }
        }

        rcu_read_unlock();
        spin_unlock(&mm->ioctx_lock);
        return res;
}

static const struct vm_operations_struct aio_ring_vm_ops = {
        .mremap         = aio_ring_mremap,
#if IS_ENABLED(CONFIG_MMU)
        .fault          = filemap_fault,
        .map_pages      = filemap_map_pages,
        .page_mkwrite   = filemap_page_mkwrite,
#endif
};

static int aio_ring_mmap(struct file *file, struct vm_area_struct *vma)
{
        vma->vm_flags |= VM_DONTEXPAND;
        vma->vm_ops = &aio_ring_vm_ops;
        return 0;
}

static const struct file_operations aio_ring_fops = {
        .mmap = aio_ring_mmap,
};

#if IS_ENABLED(CONFIG_MIGRATION)
static int aio_migratepage(struct address_space *mapping, struct page *new,
                        struct page *old, enum migrate_mode mode)
{
        struct kioctx *ctx;
        unsigned long flags;
        pgoff_t idx;
        int rc;

        /*
         * We cannot support the _NO_COPY case here, because copy needs to
         * happen under the ctx->completion_lock. That does not work with the
         * migration workflow of MIGRATE_SYNC_NO_COPY.
         */
        if (mode == MIGRATE_SYNC_NO_COPY)
                return -EINVAL;

        rc = 0;

        /* mapping->private_lock here protects against the kioctx teardown.  */
        spin_lock(&mapping->private_lock);
        ctx = mapping->private_data;
        if (!ctx) {
                rc = -EINVAL;
                goto out;
        }

        /* The ring_lock mutex.  The prevents aio_read_events() from writing
         * to the ring's head, and prevents page migration from mucking in
         * a partially initialized kiotx.
         */
        if (!mutex_trylock(&ctx->ring_lock)) {
                rc = -EAGAIN;
                goto out;
        }

        idx = old->index;
        if (idx < (pgoff_t)ctx->nr_pages) {
                /* Make sure the old page hasn't already been changed */
                if (ctx->ring_pages[idx] != old)
                        rc = -EAGAIN;
        } else
                rc = -EINVAL;

        if (rc != 0)
                goto out_unlock;

        /* Writeback must be complete */
        BUG_ON(PageWriteback(old));
        get_page(new);

        rc = migrate_page_move_mapping(mapping, new, old, 1);
        if (rc != MIGRATEPAGE_SUCCESS) {
                put_page(new);
                goto out_unlock;
        }

        /* Take completion_lock to prevent other writes to the ring buffer
         * while the old page is copied to the new.  This prevents new
         * events from being lost.
         */
        spin_lock_irqsave(&ctx->completion_lock, flags);
        migrate_page_copy(new, old);
        BUG_ON(ctx->ring_pages[idx] != old);
        ctx->ring_pages[idx] = new;
        spin_unlock_irqrestore(&ctx->completion_lock, flags);

        /* The old page is no longer accessible. */
        put_page(old);

out_unlock:
        mutex_unlock(&ctx->ring_lock);
out:
        spin_unlock(&mapping->private_lock);
        return rc;
}
#endif

static const struct address_space_operations aio_ctx_aops = {
        .set_page_dirty = __set_page_dirty_no_writeback,
#if IS_ENABLED(CONFIG_MIGRATION)
        .migratepage    = aio_migratepage,
#endif
};

static int aio_setup_ring(struct kioctx *ctx, unsigned int nr_events)
{
        struct aio_ring *ring;
        struct mm_struct *mm = current->mm;
        unsigned long size, unused;
        int nr_pages;
        int i;
        struct file *file;

        /* Compensate for the ring buffer's head/tail overlap entry */
        nr_events += 2; /* 1 is required, 2 for good luck */

        size = sizeof(struct aio_ring);
        size += sizeof(struct io_event) * nr_events;

        nr_pages = PFN_UP(size);
        if (nr_pages < 0)
                return -EINVAL;

        file = aio_private_file(ctx, nr_pages);
        if (IS_ERR(file)) {
                ctx->aio_ring_file = NULL;
                return -ENOMEM;
        }

        ctx->aio_ring_file = file;
        nr_events = (PAGE_SIZE * nr_pages - sizeof(struct aio_ring))
                        / sizeof(struct io_event);

        ctx->ring_pages = ctx->internal_pages;
        if (nr_pages > AIO_RING_PAGES) {
                ctx->ring_pages = kcalloc(nr_pages, sizeof(struct page *),
                                          GFP_KERNEL);
                if (!ctx->ring_pages) {
                        put_aio_ring_file(ctx);
                        return -ENOMEM;
                }
        }

        for (i = 0; i < nr_pages; i++) {
                struct page *page;
                page = find_or_create_page(file->f_mapping,
                                           i, GFP_HIGHUSER | __GFP_ZERO);
                if (!page)
                        break;
                pr_debug("pid(%d) page[%d]->count=%d\n",
                         current->pid, i, page_count(page));
                SetPageUptodate(page);
                unlock_page(page);

                ctx->ring_pages[i] = page;
        }
        ctx->nr_pages = i;

        if (unlikely(i != nr_pages)) {
                aio_free_ring(ctx);
                return -ENOMEM;
        }

        ctx->mmap_size = nr_pages * PAGE_SIZE;
        pr_debug("attempting mmap of %lu bytes\n", ctx->mmap_size);

        if (mmap_write_lock_killable(mm)) {
                ctx->mmap_size = 0;
                aio_free_ring(ctx);
                return -EINTR;
        }

        ctx->mmap_base = do_mmap(ctx->aio_ring_file, 0, ctx->mmap_size,
                                 PROT_READ | PROT_WRITE,
                                 MAP_SHARED, 0, &unused, NULL);
        mmap_write_unlock(mm);
        if (IS_ERR((void *)ctx->mmap_base)) {
                ctx->mmap_size = 0;
                aio_free_ring(ctx);
                return -ENOMEM;
        }

        pr_debug("mmap address: 0x%08lx\n", ctx->mmap_base);

        ctx->user_id = ctx->mmap_base;
        ctx->nr_events = nr_events; /* trusted copy */

        ring = kmap_atomic(ctx->ring_pages[0]);
        ring->nr = nr_events;   /* user copy */
        ring->id = ~0U;
        ring->head = ring->tail = 0;
        ring->magic = AIO_RING_MAGIC;
        ring->compat_features = AIO_RING_COMPAT_FEATURES;
        ring->incompat_features = AIO_RING_INCOMPAT_FEATURES;
        ring->header_length = sizeof(struct aio_ring);
        kunmap_atomic(ring);
        flush_dcache_page(ctx->ring_pages[0]);

        return 0;
}

#define AIO_EVENTS_PER_PAGE     (PAGE_SIZE / sizeof(struct io_event))
#define AIO_EVENTS_FIRST_PAGE   ((PAGE_SIZE - sizeof(struct aio_ring)) / sizeof(struct io_event))
#define AIO_EVENTS_OFFSET       (AIO_EVENTS_PER_PAGE - AIO_EVENTS_FIRST_PAGE)

void kiocb_set_cancel_fn(struct kiocb *iocb, kiocb_cancel_fn *cancel)
{
        struct aio_kiocb *req = container_of(iocb, struct aio_kiocb, rw);
        struct kioctx *ctx = req->ki_ctx;
        unsigned long flags;

        if (WARN_ON_ONCE(!list_empty(&req->ki_list)))
                return;

        spin_lock_irqsave(&ctx->ctx_lock, flags);
        list_add_tail(&req->ki_list, &ctx->active_reqs);
        req->ki_cancel = cancel;
        spin_unlock_irqrestore(&ctx->ctx_lock, flags);
}
EXPORT_SYMBOL(kiocb_set_cancel_fn);

/*
 * free_ioctx() should be RCU delayed to synchronize against the RCU
 * protected lookup_ioctx() and also needs process context to call
 * aio_free_ring().  Use rcu_work.
 */
static void free_ioctx(struct work_struct *work)
{
        struct kioctx *ctx = container_of(to_rcu_work(work), struct kioctx,
                                          free_rwork);
        pr_debug("freeing %p\n", ctx);

        aio_free_ring(ctx);
        free_percpu(ctx->cpu);
        percpu_ref_exit(&ctx->reqs);
        percpu_ref_exit(&ctx->users);
        kmem_cache_free(kioctx_cachep, ctx);
}

static void free_ioctx_reqs(struct percpu_ref *ref)
{
        struct kioctx *ctx = container_of(ref, struct kioctx, reqs);

        /* At this point we know that there are no any in-flight requests */
        if (ctx->rq_wait && atomic_dec_and_test(&ctx->rq_wait->count))
                complete(&ctx->rq_wait->comp);

        /* Synchronize against RCU protected table->table[] dereferences */
        INIT_RCU_WORK(&ctx->free_rwork, free_ioctx);
        queue_rcu_work(system_wq, &ctx->free_rwork);
}

/*
 * When this function runs, the kioctx has been removed from the "hash table"
 * and ctx->users has dropped to 0, so we know no more kiocbs can be submitted -
 * now it's safe to cancel any that need to be.
 */
static void free_ioctx_users(struct percpu_ref *ref)
{
        struct kioctx *ctx = container_of(ref, struct kioctx, users);
        struct aio_kiocb *req;

        spin_lock_irq(&ctx->ctx_lock);

        while (!list_empty(&ctx->active_reqs)) {
                req = list_first_entry(&ctx->active_reqs,
                                       struct aio_kiocb, ki_list);
                req->ki_cancel(&req->rw);
                list_del_init(&req->ki_list);
        }

        spin_unlock_irq(&ctx->ctx_lock);

        percpu_ref_kill(&ctx->reqs);
        percpu_ref_put(&ctx->reqs);
}

static int ioctx_add_table(struct kioctx *ctx, struct mm_struct *mm)
{
        unsigned i, new_nr;
        struct kioctx_table *table, *old;
        struct aio_ring *ring;

        spin_lock(&mm->ioctx_lock);
        table = rcu_dereference_raw(mm->ioctx_table);

        while (1) {
                if (table)
                        for (i = 0; i < table->nr; i++)
                                if (!rcu_access_pointer(table->table[i])) {
                                        ctx->id = i;
                                        rcu_assign_pointer(table->table[i], ctx);
                                        spin_unlock(&mm->ioctx_lock);

                                        /* While kioctx setup is in progress,
                                         * we are protected from page migration
                                         * changes ring_pages by ->ring_lock.
                                         */
                                        ring = kmap_atomic(ctx->ring_pages[0]);
                                        ring->id = ctx->id;
                                        kunmap_atomic(ring);
                                        return 0;
                                }

                new_nr = (table ? table->nr : 1) * 4;
                spin_unlock(&mm->ioctx_lock);

                table = kzalloc(sizeof(*table) + sizeof(struct kioctx *) *
                                new_nr, GFP_KERNEL);
                if (!table)
                        return -ENOMEM;

                table->nr = new_nr;

                spin_lock(&mm->ioctx_lock);
                old = rcu_dereference_raw(mm->ioctx_table);

                if (!old) {
                        rcu_assign_pointer(mm->ioctx_table, table);
                } else if (table->nr > old->nr) {
                        memcpy(table->table, old->table,
                               old->nr * sizeof(struct kioctx *));

                        rcu_assign_pointer(mm->ioctx_table, table);
                        kfree_rcu(old, rcu);
                } else {
                        kfree(table);
                        table = old;
                }
        }
}

static void aio_nr_sub(unsigned nr)
{
        spin_lock(&aio_nr_lock);
        if (WARN_ON(aio_nr - nr > aio_nr))
                aio_nr = 0;
        else
                aio_nr -= nr;
        spin_unlock(&aio_nr_lock);
}

/* ioctx_alloc
 *      Allocates and initializes an ioctx.  Returns an ERR_PTR if it failed.
 */
static struct kioctx *ioctx_alloc(unsigned nr_events)
{
        struct mm_struct *mm = current->mm;
        struct kioctx *ctx;
        int err = -ENOMEM;

        /*
         * Store the original nr_events -- what userspace passed to io_setup(),
         * for counting against the global limit -- before it changes.
         */
        unsigned int max_reqs = nr_events;

        /*
         * We keep track of the number of available ringbuffer slots, to prevent
         * overflow (reqs_available), and we also use percpu counters for this.
         *
         * So since up to half the slots might be on other cpu's percpu counters
         * and unavailable, double nr_events so userspace sees what they
         * expected: additionally, we move req_batch slots to/from percpu
         * counters at a time, so make sure that isn't 0:
         */
        nr_events = max(nr_events, num_possible_cpus() * 4);
        nr_events *= 2;

        /* Prevent overflows */
        if (nr_events > (0x10000000U / sizeof(struct io_event))) {
                pr_debug("ENOMEM: nr_events too high\n");
                return ERR_PTR(-EINVAL);
        }

        if (!nr_events || (unsigned long)max_reqs > aio_max_nr)
                return ERR_PTR(-EAGAIN);

        ctx = kmem_cache_zalloc(kioctx_cachep, GFP_KERNEL);
        if (!ctx)
                return ERR_PTR(-ENOMEM);

        ctx->max_reqs = max_reqs;

        spin_lock_init(&ctx->ctx_lock);
        spin_lock_init(&ctx->completion_lock);
        mutex_init(&ctx->ring_lock);
        /* Protect against page migration throughout kiotx setup by keeping
         * the ring_lock mutex held until setup is complete. */
        mutex_lock(&ctx->ring_lock);
        init_waitqueue_head(&ctx->wait);

        INIT_LIST_HEAD(&ctx->active_reqs);

        if (percpu_ref_init(&ctx->users, free_ioctx_users, 0, GFP_KERNEL))
                goto err;

        if (percpu_ref_init(&ctx->reqs, free_ioctx_reqs, 0, GFP_KERNEL))
                goto err;

        ctx->cpu = alloc_percpu(struct kioctx_cpu);
        if (!ctx->cpu)
                goto err;

        err = aio_setup_ring(ctx, nr_events);
        if (err < 0)
                goto err;

        atomic_set(&ctx->reqs_available, ctx->nr_events - 1);
        ctx->req_batch = (ctx->nr_events - 1) / (num_possible_cpus() * 4);
        if (ctx->req_batch < 1)
                ctx->req_batch = 1;

        /* limit the number of system wide aios */
        spin_lock(&aio_nr_lock);
        if (aio_nr + ctx->max_reqs > aio_max_nr ||
            aio_nr + ctx->max_reqs < aio_nr) {
                spin_unlock(&aio_nr_lock);
                err = -EAGAIN;
                goto err_ctx;
        }
        aio_nr += ctx->max_reqs;
        spin_unlock(&aio_nr_lock);

        percpu_ref_get(&ctx->users);    /* io_setup() will drop this ref */
        percpu_ref_get(&ctx->reqs);     /* free_ioctx_users() will drop this */

        err = ioctx_add_table(ctx, mm);
        if (err)
                goto err_cleanup;

        /* Release the ring_lock mutex now that all setup is complete. */
        mutex_unlock(&ctx->ring_lock);

        pr_debug("allocated ioctx %p[%ld]: mm=%p mask=0x%x\n",
                 ctx, ctx->user_id, mm, ctx->nr_events);
        return ctx;

err_cleanup:
        aio_nr_sub(ctx->max_reqs);
err_ctx:
        atomic_set(&ctx->dead, 1);
        if (ctx->mmap_size)
                vm_munmap(ctx->mmap_base, ctx->mmap_size);
        aio_free_ring(ctx);
err:
        mutex_unlock(&ctx->ring_lock);
        free_percpu(ctx->cpu);
        percpu_ref_exit(&ctx->reqs);
        percpu_ref_exit(&ctx->users);
        kmem_cache_free(kioctx_cachep, ctx);
        pr_debug("error allocating ioctx %d\n", err);
        return ERR_PTR(err);
}

/* kill_ioctx
 *      Cancels all outstanding aio requests on an aio context.  Used
 *      when the processes owning a context have all exited to encourage
 *      the rapid destruction of the kioctx.
 */
static int kill_ioctx(struct mm_struct *mm, struct kioctx *ctx,
                      struct ctx_rq_wait *wait)
{
        struct kioctx_table *table;

        spin_lock(&mm->ioctx_lock);
        if (atomic_xchg(&ctx->dead, 1)) {
                spin_unlock(&mm->ioctx_lock);
                return -EINVAL;
        }

        table = rcu_dereference_raw(mm->ioctx_table);
        WARN_ON(ctx != rcu_access_pointer(table->table[ctx->id]));
        RCU_INIT_POINTER(table->table[ctx->id], NULL);
        spin_unlock(&mm->ioctx_lock);

        /* free_ioctx_reqs() will do the necessary RCU synchronization */
        wake_up_all(&ctx->wait);

        /*
         * It'd be more correct to do this in free_ioctx(), after all
         * the outstanding kiocbs have finished - but by then io_destroy
         * has already returned, so io_setup() could potentially return
         * -EAGAIN with no ioctxs actually in use (as far as userspace
         *  could tell).
         */
        aio_nr_sub(ctx->max_reqs);

        if (ctx->mmap_size)
                vm_munmap(ctx->mmap_base, ctx->mmap_size);

        ctx->rq_wait = wait;
        percpu_ref_kill(&ctx->users);
        return 0;
}

/*
 * exit_aio: called when the last user of mm goes away.  At this point, there is
 * no way for any new requests to be submited or any of the io_* syscalls to be
 * called on the context.
 *
 * There may be outstanding kiocbs, but free_ioctx() will explicitly wait on
 * them.
 */
void exit_aio(struct mm_struct *mm)
{
        struct kioctx_table *table = rcu_dereference_raw(mm->ioctx_table);
        struct ctx_rq_wait wait;
        int i, skipped;

        if (!table)
                return;

        atomic_set(&wait.count, table->nr);
        init_completion(&wait.comp);

        skipped = 0;
        for (i = 0; i < table->nr; ++i) {
                struct kioctx *ctx =
                        rcu_dereference_protected(table->table[i], true);

                if (!ctx) {
                        skipped++;
                        continue;
                }

                /*
                 * We don't need to bother with munmap() here - exit_mmap(mm)
                 * is coming and it'll unmap everything. And we simply can't,
                 * this is not necessarily our ->mm.
                 * Since kill_ioctx() uses non-zero ->mmap_size as indicator
                 * that it needs to unmap the area, just set it to 0.
                 */
                ctx->mmap_size = 0;
                kill_ioctx(mm, ctx, &wait);
        }

        if (!atomic_sub_and_test(skipped, &wait.count)) {
                /* Wait until all IO for the context are done. */
                wait_for_completion(&wait.comp);
        }

        RCU_INIT_POINTER(mm->ioctx_table, NULL);
        kfree(table);
}

static void put_reqs_available(struct kioctx *ctx, unsigned nr)
{
        struct kioctx_cpu *kcpu;
        unsigned long flags;

        local_irq_save(flags);
        kcpu = this_cpu_ptr(ctx->cpu);
        kcpu->reqs_available += nr;

        while (kcpu->reqs_available >= ctx->req_batch * 2) {
                kcpu->reqs_available -= ctx->req_batch;
                atomic_add(ctx->req_batch, &ctx->reqs_available);
        }

        local_irq_restore(flags);
}

static bool __get_reqs_available(struct kioctx *ctx)
{
        struct kioctx_cpu *kcpu;
        bool ret = false;
        unsigned long flags;

        local_irq_save(flags);
        kcpu = this_cpu_ptr(ctx->cpu);
        if (!kcpu->reqs_available) {
                int old, avail = atomic_read(&ctx->reqs_available);

                do {
                        if (avail < ctx->req_batch)
                                goto out;

                        old = avail;
                        avail = atomic_cmpxchg(&ctx->reqs_available,
                                               avail, avail - ctx->req_batch);
                } while (avail != old);

                kcpu->reqs_available += ctx->req_batch;
        }

        ret = true;
        kcpu->reqs_available--;
out:
        local_irq_restore(flags);
        return ret;
}

/* refill_reqs_available
 *      Updates the reqs_available reference counts used for tracking the
 *      number of free slots in the completion ring.  This can be called
 *      from aio_complete() (to optimistically update reqs_available) or
 *      from aio_get_req() (the we're out of events case).  It must be
 *      called holding ctx->completion_lock.
 */
static void refill_reqs_available(struct kioctx *ctx, unsigned head,
                                  unsigned tail)
{
        unsigned events_in_ring, completed;

        /* Clamp head since userland can write to it. */
        head %= ctx->nr_events;
        if (head <= tail)
                events_in_ring = tail - head;
        else
                events_in_ring = ctx->nr_events - (head - tail);

        completed = ctx->completed_events;
        if (events_in_ring < completed)
                completed -= events_in_ring;
        else
                completed = 0;

        if (!completed)
                return;

        ctx->completed_events -= completed;
        put_reqs_available(ctx, completed);
}

/* user_refill_reqs_available
 *      Called to refill reqs_available when aio_get_req() encounters an
 *      out of space in the completion ring.
 */
static void user_refill_reqs_available(struct kioctx *ctx)
{
        spin_lock_irq(&ctx->completion_lock);
        if (ctx->completed_events) {
                struct aio_ring *ring;
                unsigned head;

                /* Access of ring->head may race with aio_read_events_ring()
                 * here, but that's okay since whether we read the old version
                 * or the new version, and either will be valid.  The important
                 * part is that head cannot pass tail since we prevent
                 * aio_complete() from updating tail by holding
                 * ctx->completion_lock.  Even if head is invalid, the check
                 * against ctx->completed_events below will make sure we do the
                 * safe/right thing.
                 */
                ring = kmap_atomic(ctx->ring_pages[0]);
                head = ring->head;
                kunmap_atomic(ring);

                refill_reqs_available(ctx, head, ctx->tail);
        }

        spin_unlock_irq(&ctx->completion_lock);
}

static bool get_reqs_available(struct kioctx *ctx)
{
        if (__get_reqs_available(ctx))
                return true;
        user_refill_reqs_available(ctx);
        return __get_reqs_available(ctx);
}

/* aio_get_req
 *      Allocate a slot for an aio request.
 * Returns NULL if no requests are free.
 *
 * The refcount is initialized to 2 - one for the async op completion,
 * one for the synchronous code that does this.
 */
static inline struct aio_kiocb *aio_get_req(struct kioctx *ctx)
{
        struct aio_kiocb *req;

        req = kmem_cache_alloc(kiocb_cachep, GFP_KERNEL);
        if (unlikely(!req))
                return NULL;

        if (unlikely(!get_reqs_available(ctx))) {
                kmem_cache_free(kiocb_cachep, req);
                return NULL;
        }

        percpu_ref_get(&ctx->reqs);
        req->ki_ctx = ctx;
        INIT_LIST_HEAD(&req->ki_list);
        refcount_set(&req->ki_refcnt, 2);
        req->ki_eventfd = NULL;
        return req;
}

static struct kioctx *lookup_ioctx(unsigned long ctx_id)
{
        struct aio_ring __user *ring  = (void __user *)ctx_id;
        struct mm_struct *mm = current->mm;
        struct kioctx *ctx, *ret = NULL;
        struct kioctx_table *table;
        unsigned id;

        if (get_user(id, &ring->id))
                return NULL;

        rcu_read_lock();
        table = rcu_dereference(mm->ioctx_table);

        if (!table || id >= table->nr)
                goto out;

        id = array_index_nospec(id, table->nr);
        ctx = rcu_dereference(table->table[id]);
        if (ctx && ctx->user_id == ctx_id) {
                if (percpu_ref_tryget_live(&ctx->users))
                        ret = ctx;
        }
out:
        rcu_read_unlock();
        return ret;
}

static inline void iocb_destroy(struct aio_kiocb *iocb)
{
        if (iocb->ki_eventfd)
                eventfd_ctx_put(iocb->ki_eventfd);
        if (iocb->ki_filp)
                fput(iocb->ki_filp);
        percpu_ref_put(&iocb->ki_ctx->reqs);
        kmem_cache_free(kiocb_cachep, iocb);
}

/* aio_complete
 *      Called when the io request on the given iocb is complete.
 */
static void aio_complete(struct aio_kiocb *iocb)
{
        struct kioctx   *ctx = iocb->ki_ctx;
        struct aio_ring *ring;
        struct io_event *ev_page, *event;
        unsigned tail, pos, head;
        unsigned long   flags;

        /*
         * Add a completion event to the ring buffer. Must be done holding
         * ctx->completion_lock to prevent other code from messing with the tail
         * pointer since we might be called from irq context.
         */
        spin_lock_irqsave(&ctx->completion_lock, flags);

        tail = ctx->tail;
        pos = tail + AIO_EVENTS_OFFSET;

        if (++tail >= ctx->nr_events)
                tail = 0;

        ev_page = kmap_atomic(ctx->ring_pages[pos / AIO_EVENTS_PER_PAGE]);
        event = ev_page + pos % AIO_EVENTS_PER_PAGE;

        *event = iocb->ki_res;

        kunmap_atomic(ev_page);
        flush_dcache_page(ctx->ring_pages[pos / AIO_EVENTS_PER_PAGE]);

        pr_debug("%p[%u]: %p: %p %Lx %Lx %Lx\n", ctx, tail, iocb,
                 (void __user *)(unsigned long)iocb->ki_res.obj,
                 iocb->ki_res.data, iocb->ki_res.res, iocb->ki_res.res2);

        /* after flagging the request as done, we
         * must never even look at it again
         */
        smp_wmb();      /* make event visible before updating tail */

        ctx->tail = tail;

        ring = kmap_atomic(ctx->ring_pages[0]);
        head = ring->head;
        ring->tail = tail;
        kunmap_atomic(ring);
        flush_dcache_page(ctx->ring_pages[0]);

        ctx->completed_events++;
        if (ctx->completed_events > 1)
                refill_reqs_available(ctx, head, tail);
        spin_unlock_irqrestore(&ctx->completion_lock, flags);

        pr_debug("added to ring %p at [%u]\n", iocb, tail);

        /*
         * Check if the user asked us to deliver the result through an
         * eventfd. The eventfd_signal() function is safe to be called
         * from IRQ context.
         */
        if (iocb->ki_eventfd)
                eventfd_signal(iocb->ki_eventfd, 1);

        /*
         * We have to order our ring_info tail store above and test
         * of the wait list below outside the wait lock.  This is
         * like in wake_up_bit() where clearing a bit has to be
         * ordered with the unlocked test.
         */
        smp_mb();

        if (waitqueue_active(&ctx->wait))
                wake_up(&ctx->wait);
}

static inline void iocb_put(struct aio_kiocb *iocb)
{
        if (refcount_dec_and_test(&iocb->ki_refcnt)) {
                aio_complete(iocb);
                iocb_destroy(iocb);
        }
}

/* aio_read_events_ring
 *      Pull an event off of the ioctx's event ring.  Returns the number of
 *      events fetched
 */
static long aio_read_events_ring(struct kioctx *ctx,
                                 struct io_event __user *event, long nr)
{
        struct aio_ring *ring;
        unsigned head, tail, pos;
        long ret = 0;
        int copy_ret;

        /*
         * The mutex can block and wake us up and that will cause
         * wait_event_interruptible_hrtimeout() to schedule without sleeping
         * and repeat. This should be rare enough that it doesn't cause
         * peformance issues. See the comment in read_events() for more detail.
         */
        sched_annotate_sleep();
        mutex_lock(&ctx->ring_lock);

        /* Access to ->ring_pages here is protected by ctx->ring_lock. */
        ring = kmap_atomic(ctx->ring_pages[0]);
        head = ring->head;
        tail = ring->tail;
        kunmap_atomic(ring);

        /*
         * Ensure that once we've read the current tail pointer, that
         * we also see the events that were stored up to the tail.
         */
        smp_rmb();

        pr_debug("h%u t%u m%u\n", head, tail, ctx->nr_events);

        if (head == tail)
                goto out;

        head %= ctx->nr_events;
        tail %= ctx->nr_events;

        while (ret < nr) {
                long avail;
                struct io_event *ev;
                struct page *page;

                avail = (head <= tail ?  tail : ctx->nr_events) - head;
                if (head == tail)
                        break;

                pos = head + AIO_EVENTS_OFFSET;
                page = ctx->ring_pages[pos / AIO_EVENTS_PER_PAGE];
                pos %= AIO_EVENTS_PER_PAGE;

                avail = min(avail, nr - ret);
                avail = min_t(long, avail, AIO_EVENTS_PER_PAGE - pos);

                ev = kmap(page);
                copy_ret = copy_to_user(event + ret, ev + pos,
                                        sizeof(*ev) * avail);
                kunmap(page);

                if (unlikely(copy_ret)) {
                        ret = -EFAULT;
                        goto out;
                }

                ret += avail;
                head += avail;
                head %= ctx->nr_events;
        }

        ring = kmap_atomic(ctx->ring_pages[0]);
        ring->head = head;
        kunmap_atomic(ring);
        flush_dcache_page(ctx->ring_pages[0]);

        pr_debug("%li  h%u t%u\n", ret, head, tail);
out:
        mutex_unlock(&ctx->ring_lock);

        return ret;
}

static bool aio_read_events(struct kioctx *ctx, long min_nr, long nr,
                            struct io_event __user *event, long *i)
{
        long ret = aio_read_events_ring(ctx, event + *i, nr - *i);

        if (ret > 0)
                *i += ret;

        if (unlikely(atomic_read(&ctx->dead)))
                ret = -EINVAL;

        if (!*i)
                *i = ret;

        return ret < 0 || *i >= min_nr;
}

static long read_events(struct kioctx *ctx, long min_nr, long nr,
                        struct io_event __user *event,
                        ktime_t until)
{
        long ret = 0;

        /*
         * Note that aio_read_events() is being called as the conditional - i.e.
         * we're calling it after prepare_to_wait() has set task state to
         * TASK_INTERRUPTIBLE.
         *
         * But aio_read_events() can block, and if it blocks it's going to flip
         * the task state back to TASK_RUNNING.
         *
         * This should be ok, provided it doesn't flip the state back to
         * TASK_RUNNING and return 0 too much - that causes us to spin. That
         * will only happen if the mutex_lock() call blocks, and we then find
         * the ringbuffer empty. So in practice we should be ok, but it's
         * something to be aware of when touching this code.
         */
        if (until == 0)
                aio_read_events(ctx, min_nr, nr, event, &ret);
        else
                wait_event_interruptible_hrtimeout(ctx->wait,
                                aio_read_events(ctx, min_nr, nr, event, &ret),
                                until);
        return ret;
}

/* sys_io_setup:
 *      Create an aio_context capable of receiving at least nr_events.
 *      ctxp must not point to an aio_context that already exists, and
 *      must be initialized to 0 prior to the call.  On successful
 *      creation of the aio_context, *ctxp is filled in with the resulting 
 *      handle.  May fail with -EINVAL if *ctxp is not initialized,
 *      if the specified nr_events exceeds internal limits.  May fail 
 *      with -EAGAIN if the specified nr_events exceeds the user's limit 
 *      of available events.  May fail with -ENOMEM if insufficient kernel
 *      resources are available.  May fail with -EFAULT if an invalid
 *      pointer is passed for ctxp.  Will fail with -ENOSYS if not
 *      implemented.
 */
SYSCALL_DEFINE2(io_setup, unsigned, nr_events, aio_context_t __user *, ctxp)
{
        struct kioctx *ioctx = NULL;
        unsigned long ctx;
        long ret;

        ret = get_user(ctx, ctxp);
        if (unlikely(ret))
                goto out;

        ret = -EINVAL;
        if (unlikely(ctx || nr_events == 0)) {
                pr_debug("EINVAL: ctx %lu nr_events %u\n",
                         ctx, nr_events);
                goto out;
        }

        ioctx = ioctx_alloc(nr_events);
        ret = PTR_ERR(ioctx);
        if (!IS_ERR(ioctx)) {
                ret = put_user(ioctx->user_id, ctxp);
                if (ret)
                        kill_ioctx(current->mm, ioctx, NULL);
                percpu_ref_put(&ioctx->users);
        }

out:
        return ret;
}

#ifdef CONFIG_COMPAT
COMPAT_SYSCALL_DEFINE2(io_setup, unsigned, nr_events, u32 __user *, ctx32p)
{
        struct kioctx *ioctx = NULL;
        unsigned long ctx;
        long ret;

        ret = get_user(ctx, ctx32p);
        if (unlikely(ret))
                goto out;

        ret = -EINVAL;
        if (unlikely(ctx || nr_events == 0)) {
                pr_debug("EINVAL: ctx %lu nr_events %u\n",
                         ctx, nr_events);
                goto out;
        }

        ioctx = ioctx_alloc(nr_events);
        ret = PTR_ERR(ioctx);
        if (!IS_ERR(ioctx)) {
                /* truncating is ok because it's a user address */
                ret = put_user((u32)ioctx->user_id, ctx32p);
                if (ret)
                        kill_ioctx(current->mm, ioctx, NULL);
                percpu_ref_put(&ioctx->users);
        }

out:
        return ret;
}
#endif

/* sys_io_destroy:
 *      Destroy the aio_context specified.  May cancel any outstanding 
 *      AIOs and block on completion.  Will fail with -ENOSYS if not
 *      implemented.  May fail with -EINVAL if the context pointed to
 *      is invalid.
 */
SYSCALL_DEFINE1(io_destroy, aio_context_t, ctx)
{
        struct kioctx *ioctx = lookup_ioctx(ctx);
        if (likely(NULL != ioctx)) {
                struct ctx_rq_wait wait;
                int ret;

                init_completion(&wait.comp);
                atomic_set(&wait.count, 1);

                /* Pass requests_done to kill_ioctx() where it can be set
                 * in a thread-safe way. If we try to set it here then we have
                 * a race condition if two io_destroy() called simultaneously.
                 */
                ret = kill_ioctx(current->mm, ioctx, &wait);
                percpu_ref_put(&ioctx->users);

                /* Wait until all IO for the context are done. Otherwise kernel
                 * keep using user-space buffers even if user thinks the context
                 * is destroyed.
                 */
                if (!ret)
                        wait_for_completion(&wait.comp);

                return ret;
        }
        pr_debug("EINVAL: invalid context id\n");
        return -EINVAL;
}

static void aio_remove_iocb(struct aio_kiocb *iocb)
{
        struct kioctx *ctx = iocb->ki_ctx;
        unsigned long flags;

        spin_lock_irqsave(&ctx->ctx_lock, flags);
        list_del(&iocb->ki_list);
        spin_unlock_irqrestore(&ctx->ctx_lock, flags);
}

static void aio_complete_rw(struct kiocb *kiocb, long res, long res2)
{
        struct aio_kiocb *iocb = container_of(kiocb, struct aio_kiocb, rw);

        if (!list_empty_careful(&iocb->ki_list))
                aio_remove_iocb(iocb);

        if (kiocb->ki_flags & IOCB_WRITE) {
                struct inode *inode = file_inode(kiocb->ki_filp);

                /*
                 * Tell lockdep we inherited freeze protection from submission
                 * thread.
                 */
                if (S_ISREG(inode->i_mode))
                        __sb_writers_acquired(inode->i_sb, SB_FREEZE_WRITE);
                file_end_write(kiocb->ki_filp);
        }

        iocb->ki_res.res = res;
        iocb->ki_res.res2 = res2;
        iocb_put(iocb);
}

static int aio_prep_rw(struct kiocb *req, const struct iocb *iocb)
{
        int ret;

        req->ki_complete = aio_complete_rw;
        req->private = NULL;
        req->ki_pos = iocb->aio_offset;
        req->ki_flags = iocb_flags(req->ki_filp);
        if (iocb->aio_flags & IOCB_FLAG_RESFD)
                req->ki_flags |= IOCB_EVENTFD;
        req->ki_hint = ki_hint_validate(file_write_hint(req->ki_filp));
        if (iocb->aio_flags & IOCB_FLAG_IOPRIO) {
                /*
                 * If the IOCB_FLAG_IOPRIO flag of aio_flags is set, then
                 * aio_reqprio is interpreted as an I/O scheduling
                 * class and priority.
                 */
                ret = ioprio_check_cap(iocb->aio_reqprio);
                if (ret) {
                        pr_debug("aio ioprio check cap error: %d\n", ret);
                        return ret;
                }

                req->ki_ioprio = iocb->aio_reqprio;
        } else
                req->ki_ioprio = get_current_ioprio();

        ret = kiocb_set_rw_flags(req, iocb->aio_rw_flags);
        if (unlikely(ret))
                return ret;

        req->ki_flags &= ~IOCB_HIPRI; /* no one is going to poll for this I/O */
        return 0;
}

static ssize_t aio_setup_rw(int rw, const struct iocb *iocb,
                struct iovec **iovec, bool vectored, bool compat,
                struct iov_iter *iter)
{
        void __user *buf = (void __user *)(uintptr_t)iocb->aio_buf;
        size_t len = iocb->aio_nbytes;

        if (!vectored) {
                ssize_t ret = import_single_range(rw, buf, len, *iovec, iter);
                *iovec = NULL;
                return ret;
        }

        return __import_iovec(rw, buf, len, UIO_FASTIOV, iovec, iter, compat);
}

static inline void aio_rw_done(struct kiocb *req, ssize_t ret)
{
        switch (ret) {
        case -EIOCBQUEUED:
                break;
        case -ERESTARTSYS:
        case -ERESTARTNOINTR:
        case -ERESTARTNOHAND:
        case -ERESTART_RESTARTBLOCK:
                /*
                 * There's no easy way to restart the syscall since other AIO's
                 * may be already running. Just fail this IO with EINTR.
                 */
                ret = -EINTR;
                fallthrough;
        default:
                req->ki_complete(req, ret, 0);
        }
}

static int aio_read(struct kiocb *req, const struct iocb *iocb,
                        bool vectored, bool compat)
{
        struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
        struct iov_iter iter;
        struct file *file;
        int ret;

        ret = aio_prep_rw(req, iocb);
        if (ret)
                return ret;
        file = req->ki_filp;
        if (unlikely(!(file->f_mode & FMODE_READ)))
                return -EBADF;
        ret = -EINVAL;
        if (unlikely(!file->f_op->read_iter))
                return -EINVAL;

        ret = aio_setup_rw(READ, iocb, &iovec, vectored, compat, &iter);
        if (ret < 0)
                return ret;
        ret = rw_verify_area(READ, file, &req->ki_pos, iov_iter_count(&iter));
        if (!ret)
                aio_rw_done(req, call_read_iter(file, req, &iter));
        kfree(iovec);
        return ret;
}

static int aio_write(struct kiocb *req, const struct iocb *iocb,
                         bool vectored, bool compat)
{
        struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
        struct iov_iter iter;
        struct file *file;
        int ret;

        ret = aio_prep_rw(req, iocb);
        if (ret)
                return ret;
        file = req->ki_filp;

        if (unlikely(!(file->f_mode & FMODE_WRITE)))
                return -EBADF;
        if (unlikely(!file->f_op->write_iter))
                return -EINVAL;

        ret = aio_setup_rw(WRITE, iocb, &iovec, vectored, compat, &iter);
        if (ret < 0)
                return ret;
        ret = rw_verify_area(WRITE, file, &req->ki_pos, iov_iter_count(&iter));
        if (!ret) {
                /*
                 * Open-code file_start_write here to grab freeze protection,
                 * which will be released by another thread in
                 * aio_complete_rw().  Fool lockdep by telling it the lock got
                 * released so that it doesn't complain about the held lock when
                 * we return to userspace.
                 */
                if (S_ISREG(file_inode(file)->i_mode)) {
                        sb_start_write(file_inode(file)->i_sb);
                        __sb_writers_release(file_inode(file)->i_sb, SB_FREEZE_WRITE);
                }
                req->ki_flags |= IOCB_WRITE;
                aio_rw_done(req, call_write_iter(file, req, &iter));
        }
        kfree(iovec);
        return ret;
}

static void aio_fsync_work(struct work_struct *work)
{
        struct aio_kiocb *iocb = container_of(work, struct aio_kiocb, fsync.work);
        const struct cred *old_cred = override_creds(iocb->fsync.creds);

        iocb->ki_res.res = vfs_fsync(iocb->fsync.file, iocb->fsync.datasync);
        revert_creds(old_cred);
        put_cred(iocb->fsync.creds);
        iocb_put(iocb);
}

static int aio_fsync(struct fsync_iocb *req, const struct iocb *iocb,
                     bool datasync)
{
        if (unlikely(iocb->aio_buf || iocb->aio_offset || iocb->aio_nbytes ||
                        iocb->aio_rw_flags))
                return -EINVAL;

        if (unlikely(!req->file->f_op->fsync))
                return -EINVAL;

        req->creds = prepare_creds();
        if (!req->creds)
                return -ENOMEM;

        req->datasync = datasync;
        INIT_WORK(&req->work, aio_fsync_work);
        schedule_work(&req->work);
        return 0;
}

static void aio_poll_put_work(struct work_struct *work)
{
        struct poll_iocb *req = container_of(work, struct poll_iocb, work);
        struct aio_kiocb *iocb = container_of(req, struct aio_kiocb, poll);

        iocb_put(iocb);
}

static void aio_poll_complete_work(struct work_struct *work)
{
        struct poll_iocb *req = container_of(work, struct poll_iocb, work);
        struct aio_kiocb *iocb = container_of(req, struct aio_kiocb, poll);
        struct poll_table_struct pt = { ._key = req->events };
        struct kioctx *ctx = iocb->ki_ctx;
        __poll_t mask = 0;

        if (!READ_ONCE(req->cancelled))
                mask = vfs_poll(req->file, &pt) & req->events;

        /*
         * Note that ->ki_cancel callers also delete iocb from active_reqs after
         * calling ->ki_cancel.  We need the ctx_lock roundtrip here to
         * synchronize with them.  In the cancellation case the list_del_init
         * itself is not actually needed, but harmless so we keep it in to
         * avoid further branches in the fast path.
         */
        spin_lock_irq(&ctx->ctx_lock);
        if (!mask && !READ_ONCE(req->cancelled)) {
                add_wait_queue(req->head, &req->wait);
                spin_unlock_irq(&ctx->ctx_lock);
                return;
        }
        list_del_init(&iocb->ki_list);
        iocb->ki_res.res = mangle_poll(mask);
        req->done = true;
        spin_unlock_irq(&ctx->ctx_lock);

        iocb_put(iocb);
}

/* assumes we are called with irqs disabled */
static int aio_poll_cancel(struct kiocb *iocb)
{
        struct aio_kiocb *aiocb = container_of(iocb, struct aio_kiocb, rw);
        struct poll_iocb *req = &aiocb->poll;

        spin_lock(&req->head->lock);
        WRITE_ONCE(req->cancelled, true);
        if (!list_empty(&req->wait.entry)) {
                list_del_init(&req->wait.entry);
                schedule_work(&aiocb->poll.work);
        }
        spin_unlock(&req->head->lock);

        return 0;
}

static int aio_poll_wake(struct wait_queue_entry *wait, unsigned mode, int sync,
                void *key)
{
        struct poll_iocb *req = container_of(wait, struct poll_iocb, wait);
        struct aio_kiocb *iocb = container_of(req, struct aio_kiocb, poll);
        __poll_t mask = key_to_poll(key);
        unsigned long flags;

        /* for instances that support it check for an event match first: */
        if (mask && !(mask & req->events))
                return 0;

        list_del_init(&req->wait.entry);

        if (mask && spin_trylock_irqsave(&iocb->ki_ctx->ctx_lock, flags)) {
                struct kioctx *ctx = iocb->ki_ctx;

                /*
                 * Try to complete the iocb inline if we can. Use
                 * irqsave/irqrestore because not all filesystems (e.g. fuse)
                 * call this function with IRQs disabled and because IRQs
                 * have to be disabled before ctx_lock is obtained.
                 */
                list_del(&iocb->ki_list);
                iocb->ki_res.res = mangle_poll(mask);
                req->done = true;
                if (iocb->ki_eventfd && eventfd_signal_allowed()) {
                        iocb = NULL;
                        INIT_WORK(&req->work, aio_poll_put_work);
                        schedule_work(&req->work);
                }
                spin_unlock_irqrestore(&ctx->ctx_lock, flags);
                if (iocb)
                        iocb_put(iocb);
        } else {
                schedule_work(&req->work);
        }
        return 1;
}

struct aio_poll_table {
        struct poll_table_struct        pt;
        struct aio_kiocb                *iocb;
        int                             error;
};

static void
aio_poll_queue_proc(struct file *file, struct wait_queue_head *head,
                struct poll_table_struct *p)
{
        struct aio_poll_table *pt = container_of(p, struct aio_poll_table, pt);

        /* multiple wait queues per file are not supported */
        if (unlikely(pt->iocb->poll.head)) {
                pt->error = -EINVAL;
                return;
        }

        pt->error = 0;
        pt->iocb->poll.head = head;
        add_wait_queue(head, &pt->iocb->poll.wait);
}

static int aio_poll(struct aio_kiocb *aiocb, const struct iocb *iocb)
{
        struct kioctx *ctx = aiocb->ki_ctx;
        struct poll_iocb *req = &aiocb->poll;
        struct aio_poll_table apt;
        bool cancel = false;
        __poll_t mask;

        /* reject any unknown events outside the normal event mask. */
        if ((u16)iocb->aio_buf != iocb->aio_buf)
                return -EINVAL;
        /* reject fields that are not defined for poll */
        if (iocb->aio_offset || iocb->aio_nbytes || iocb->aio_rw_flags)
                return -EINVAL;

        INIT_WORK(&req->work, aio_poll_complete_work);
        req->events = demangle_poll(iocb->aio_buf) | EPOLLERR | EPOLLHUP;

        req->head = NULL;
        req->done = false;
        req->cancelled = false;

        apt.pt._qproc = aio_poll_queue_proc;
        apt.pt._key = req->events;
        apt.iocb = aiocb;
        apt.error = -EINVAL; /* same as no support for IOCB_CMD_POLL */

        /* initialized the list so that we can do list_empty checks */
        INIT_LIST_HEAD(&req->wait.entry);
        init_waitqueue_func_entry(&req->wait, aio_poll_wake);

        mask = vfs_poll(req->file, &apt.pt) & req->events;
        spin_lock_irq(&ctx->ctx_lock);
        if (likely(req->head)) {
                spin_lock(&req->head->lock);
                if (unlikely(list_empty(&req->wait.entry))) {
                        if (apt.error)
                                cancel = true;
                        apt.error = 0;
                        mask = 0;
                }
                if (mask || apt.error) {
                        list_del_init(&req->wait.entry);
                } else if (cancel) {
                        WRITE_ONCE(req->cancelled, true);
                } else if (!req->done) { /* actually waiting for an event */
                        list_add_tail(&aiocb->ki_list, &ctx->active_reqs);
                        aiocb->ki_cancel = aio_poll_cancel;
                }
                spin_unlock(&req->head->lock);
        }
        if (mask) { /* no async, we'd stolen it */
                aiocb->ki_res.res = mangle_poll(mask);
                apt.error = 0;
        }
        spin_unlock_irq(&ctx->ctx_lock);
        if (mask)
                iocb_put(aiocb);
        return apt.error;
}

static int __io_submit_one(struct kioctx *ctx, const struct iocb *iocb,
                           struct iocb __user *user_iocb, struct aio_kiocb *req,
                           bool compat)
{
        req->ki_filp = fget(iocb->aio_fildes);
        if (unlikely(!req->ki_filp))
                return -EBADF;

        if (iocb->aio_flags & IOCB_FLAG_RESFD) {
                struct eventfd_ctx *eventfd;
                /*
                 * If the IOCB_FLAG_RESFD flag of aio_flags is set, get an
                 * instance of the file* now. The file descriptor must be
                 * an eventfd() fd, and will be signaled for each completed
                 * event using the eventfd_signal() function.
                 */
                eventfd = eventfd_ctx_fdget(iocb->aio_resfd);
                if (IS_ERR(eventfd))
                        return PTR_ERR(eventfd);

                req->ki_eventfd = eventfd;
        }

        if (unlikely(put_user(KIOCB_KEY, &user_iocb->aio_key))) {
                pr_debug("EFAULT: aio_key\n");
                return -EFAULT;
        }

        req->ki_res.obj = (u64)(unsigned long)user_iocb;
        req->ki_res.data = iocb->aio_data;
        req->ki_res.res = 0;
        req->ki_res.res2 = 0;

        switch (iocb->aio_lio_opcode) {
        case IOCB_CMD_PREAD:
                return aio_read(&req->rw, iocb, false, compat);
        case IOCB_CMD_PWRITE:
                return aio_write(&req->rw, iocb, false, compat);
        case IOCB_CMD_PREADV:
                return aio_read(&req->rw, iocb, true, compat);
        case IOCB_CMD_PWRITEV:
                return aio_write(&req->rw, iocb, true, compat);
        case IOCB_CMD_FSYNC:
                return aio_fsync(&req->fsync, iocb, false);
        case IOCB_CMD_FDSYNC:
                return aio_fsync(&req->fsync, iocb, true);
        case IOCB_CMD_POLL:
                return aio_poll(req, iocb);
        default:
                pr_debug("invalid aio operation %d\n", iocb->aio_lio_opcode);
                return -EINVAL;
        }
}

static int io_submit_one(struct kioctx *ctx, struct iocb __user *user_iocb,
                         bool compat)
{
        struct aio_kiocb *req;
        struct iocb iocb;
        int err;

        if (unlikely(copy_from_user(&iocb, user_iocb, sizeof(iocb))))
                return -EFAULT;

        /* enforce forwards compatibility on users */
        if (unlikely(iocb.aio_reserved2)) {
                pr_debug("EINVAL: reserve field set\n");
                return -EINVAL;
        }

        /* prevent overflows */
        if (unlikely(
            (iocb.aio_buf != (unsigned long)iocb.aio_buf) ||
            (iocb.aio_nbytes != (size_t)iocb.aio_nbytes) ||
            ((ssize_t)iocb.aio_nbytes < 0)
           )) {
                pr_debug("EINVAL: overflow check\n");
                return -EINVAL;
        }

        req = aio_get_req(ctx);
        if (unlikely(!req))
                return -EAGAIN;

        err = __io_submit_one(ctx, &iocb, user_iocb, req, compat);

        /* Done with the synchronous reference */
        iocb_put(req);

        /*
         * If err is 0, we'd either done aio_complete() ourselves or have
         * arranged for that to be done asynchronously.  Anything non-zero
         * means that we need to destroy req ourselves.
         */
        if (unlikely(err)) {
                iocb_destroy(req);
                put_reqs_available(ctx, 1);
        }
        return err;
}

/* sys_io_submit:
 *      Queue the nr iocbs pointed to by iocbpp for processing.  Returns
 *      the number of iocbs queued.  May return -EINVAL if the aio_context
 *      specified by ctx_id is invalid, if nr is < 0, if the iocb at
 *      *iocbpp[0] is not properly initialized, if the operation specified
 *      is invalid for the file descriptor in the iocb.  May fail with
 *      -EFAULT if any of the data structures point to invalid data.  May
 *      fail with -EBADF if the file descriptor specified in the first
 *      iocb is invalid.  May fail with -EAGAIN if insufficient resources
 *      are available to queue any iocbs.  Will return 0 if nr is 0.  Will
 *      fail with -ENOSYS if not implemented.
 */
SYSCALL_DEFINE3(io_submit, aio_context_t, ctx_id, long, nr,
                struct iocb __user * __user *, iocbpp)
{
        struct kioctx *ctx;
        long ret = 0;
        int i = 0;
        struct blk_plug plug;

        if (unlikely(nr < 0))
                return -EINVAL;

        ctx = lookup_ioctx(ctx_id);
        if (unlikely(!ctx)) {
                pr_debug("EINVAL: invalid context id\n");
                return -EINVAL;
        }

        if (nr > ctx->nr_events)
                nr = ctx->nr_events;

        if (nr > AIO_PLUG_THRESHOLD)
                blk_start_plug(&plug);
        for (i = 0; i < nr; i++) {
                struct iocb __user *user_iocb;

                if (unlikely(get_user(user_iocb, iocbpp + i))) {
                        ret = -EFAULT;
                        break;
                }

                ret = io_submit_one(ctx, user_iocb, false);
                if (ret)
                        break;
        }
        if (nr > AIO_PLUG_THRESHOLD)
                blk_finish_plug(&plug);

        percpu_ref_put(&ctx->users);
        return i ? i : ret;
}

#ifdef CONFIG_COMPAT
COMPAT_SYSCALL_DEFINE3(io_submit, compat_aio_context_t, ctx_id,
                       int, nr, compat_uptr_t __user *, iocbpp)
{
        struct kioctx *ctx;
        long ret = 0;
        int i = 0;
        struct blk_plug plug;

        if (unlikely(nr < 0))
                return -EINVAL;

        ctx = lookup_ioctx(ctx_id);
        if (unlikely(!ctx)) {
                pr_debug("EINVAL: invalid context id\n");
                return -EINVAL;
        }

        if (nr > ctx->nr_events)
                nr = ctx->nr_events;

        if (nr > AIO_PLUG_THRESHOLD)
                blk_start_plug(&plug);
        for (i = 0; i < nr; i++) {
                compat_uptr_t user_iocb;

                if (unlikely(get_user(user_iocb, iocbpp + i))) {
                        ret = -EFAULT;
                        break;
                }

                ret = io_submit_one(ctx, compat_ptr(user_iocb), true);
                if (ret)
                        break;
        }
        if (nr > AIO_PLUG_THRESHOLD)
                blk_finish_plug(&plug);

        percpu_ref_put(&ctx->users);
        return i ? i : ret;
}
#endif

/* sys_io_cancel:
 *      Attempts to cancel an iocb previously passed to io_submit.  If
 *      the operation is successfully cancelled, the resulting event is
 *      copied into the memory pointed to by result without being placed
 *      into the completion queue and 0 is returned.  May fail with
 *      -EFAULT if any of the data structures pointed to are invalid.
 *      May fail with -EINVAL if aio_context specified by ctx_id is
 *      invalid.  May fail with -EAGAIN if the iocb specified was not
 *      cancelled.  Will fail with -ENOSYS if not implemented.
 */
SYSCALL_DEFINE3(io_cancel, aio_context_t, ctx_id, struct iocb __user *, iocb,
                struct io_event __user *, result)
{
        struct kioctx *ctx;
        struct aio_kiocb *kiocb;
        int ret = -EINVAL;
        u32 key;
        u64 obj = (u64)(unsigned long)iocb;

        if (unlikely(get_user(key, &iocb->aio_key)))
                return -EFAULT;
        if (unlikely(key != KIOCB_KEY))
                return -EINVAL;

        ctx = lookup_ioctx(ctx_id);
        if (unlikely(!ctx))
                return -EINVAL;

        spin_lock_irq(&ctx->ctx_lock);
        /* TODO: use a hash or array, this sucks. */
        list_for_each_entry(kiocb, &ctx->active_reqs, ki_list) {
                if (kiocb->ki_res.obj == obj) {
                        ret = kiocb->ki_cancel(&kiocb->rw);
                        list_del_init(&kiocb->ki_list);
                        break;
                }
        }
        spin_unlock_irq(&ctx->ctx_lock);

        if (!ret) {
                /*
                 * The result argument is no longer used - the io_event is
                 * always delivered via the ring buffer. -EINPROGRESS indicates
                 * cancellation is progress:
                 */
                ret = -EINPROGRESS;
        }

        percpu_ref_put(&ctx->users);

        return ret;
}

static long do_io_getevents(aio_context_t ctx_id,
                long min_nr,
                long nr,
                struct io_event __user *events,
                struct timespec64 *ts)
{
        ktime_t until = ts ? timespec64_to_ktime(*ts) : KTIME_MAX;
        struct kioctx *ioctx = lookup_ioctx(ctx_id);
        long ret = -EINVAL;

        if (likely(ioctx)) {
                if (likely(min_nr <= nr && min_nr >= 0))
                        ret = read_events(ioctx, min_nr, nr, events, until);
                percpu_ref_put(&ioctx->users);
        }

        return ret;
}

/* io_getevents:
 *      Attempts to read at least min_nr events and up to nr events from
 *      the completion queue for the aio_context specified by ctx_id. If
 *      it succeeds, the number of read events is returned. May fail with
 *      -EINVAL if ctx_id is invalid, if min_nr is out of range, if nr is
 *      out of range, if timeout is out of range.  May fail with -EFAULT
 *      if any of the memory specified is invalid.  May return 0 or
 *      < min_nr if the timeout specified by timeout has elapsed
 *      before sufficient events are available, where timeout == NULL
 *      specifies an infinite timeout. Note that the timeout pointed to by
 *      timeout is relative.  Will fail with -ENOSYS if not implemented.
 */
#ifdef CONFIG_64BIT

SYSCALL_DEFINE5(io_getevents, aio_context_t, ctx_id,
                long, min_nr,
                long, nr,
                struct io_event __user *, events,
                struct __kernel_timespec __user *, timeout)
{
        struct timespec64       ts;
        int                     ret;

        if (timeout && unlikely(get_timespec64(&ts, timeout)))
                return -EFAULT;

        ret = do_io_getevents(ctx_id, min_nr, nr, events, timeout ? &ts : NULL);
        if (!ret && signal_pending(current))
                ret = -EINTR;
        return ret;
}

#endif

struct __aio_sigset {
        const sigset_t __user   *sigmask;
        size_t          sigsetsize;
};

SYSCALL_DEFINE6(io_pgetevents,
                aio_context_t, ctx_id,
                long, min_nr,
                long, nr,
                struct io_event __user *, events,
                struct __kernel_timespec __user *, timeout,
                const struct __aio_sigset __user *, usig)
{
        struct __aio_sigset     ksig = { NULL, };
        struct timespec64       ts;
        bool interrupted;
        int ret;

        if (timeout && unlikely(get_timespec64(&ts, timeout)))
                return -EFAULT;

        if (usig && copy_from_user(&ksig, usig, sizeof(ksig)))
                return -EFAULT;

        ret = set_user_sigmask(ksig.sigmask, ksig.sigsetsize);
        if (ret)
                return ret;

        ret = do_io_getevents(ctx_id, min_nr, nr, events, timeout ? &ts : NULL);

        interrupted = signal_pending(current);
        restore_saved_sigmask_unless(interrupted);
        if (interrupted && !ret)
                ret = -ERESTARTNOHAND;

        return ret;
}

#if defined(CONFIG_COMPAT_32BIT_TIME) && !defined(CONFIG_64BIT)

SYSCALL_DEFINE6(io_pgetevents_time32,
                aio_context_t, ctx_id,
                long, min_nr,
                long, nr,
                struct io_event __user *, events,
                struct old_timespec32 __user *, timeout,
                const struct __aio_sigset __user *, usig)
{
        struct __aio_sigset     ksig = { NULL, };
        struct timespec64       ts;
        bool interrupted;
        int ret;

        if (timeout && unlikely(get_old_timespec32(&ts, timeout)))
                return -EFAULT;

        if (usig && copy_from_user(&ksig, usig, sizeof(ksig)))
                return -EFAULT;


        ret = set_user_sigmask(ksig.sigmask, ksig.sigsetsize);
        if (ret)
                return ret;

        ret = do_io_getevents(ctx_id, min_nr, nr, events, timeout ? &ts : NULL);

        interrupted = signal_pending(current);
        restore_saved_sigmask_unless(interrupted);
        if (interrupted && !ret)
                ret = -ERESTARTNOHAND;

        return ret;
}

#endif

#if defined(CONFIG_COMPAT_32BIT_TIME)

SYSCALL_DEFINE5(io_getevents_time32, __u32, ctx_id,
                __s32, min_nr,
                __s32, nr,
                struct io_event __user *, events,
                struct old_timespec32 __user *, timeout)
{
        struct timespec64 t;
        int ret;

        if (timeout && get_old_timespec32(&t, timeout))
                return -EFAULT;

        ret = do_io_getevents(ctx_id, min_nr, nr, events, timeout ? &t : NULL);
        if (!ret && signal_pending(current))
                ret = -EINTR;
        return ret;
}

#endif

#ifdef CONFIG_COMPAT

struct __compat_aio_sigset {
        compat_uptr_t           sigmask;
        compat_size_t           sigsetsize;
};

#if defined(CONFIG_COMPAT_32BIT_TIME)

COMPAT_SYSCALL_DEFINE6(io_pgetevents,
                compat_aio_context_t, ctx_id,
                compat_long_t, min_nr,
                compat_long_t, nr,
                struct io_event __user *, events,
                struct old_timespec32 __user *, timeout,
                const struct __compat_aio_sigset __user *, usig)
{
        struct __compat_aio_sigset ksig = { 0, };
        struct timespec64 t;
        bool interrupted;
        int ret;

        if (timeout && get_old_timespec32(&t, timeout))
                return -EFAULT;

        if (usig && copy_from_user(&ksig, usig, sizeof(ksig)))
                return -EFAULT;

        ret = set_compat_user_sigmask(compat_ptr(ksig.sigmask), ksig.sigsetsize);
        if (ret)
                return ret;

        ret = do_io_getevents(ctx_id, min_nr, nr, events, timeout ? &t : NULL);

        interrupted = signal_pending(current);
        restore_saved_sigmask_unless(interrupted);
        if (interrupted && !ret)
                ret = -ERESTARTNOHAND;

        return ret;
}

#endif

COMPAT_SYSCALL_DEFINE6(io_pgetevents_time64,
                compat_aio_context_t, ctx_id,
                compat_long_t, min_nr,
                compat_long_t, nr,
                struct io_event __user *, events,
                struct __kernel_timespec __user *, timeout,
                const struct __compat_aio_sigset __user *, usig)
{
        struct __compat_aio_sigset ksig = { 0, };
        struct timespec64 t;
        bool interrupted;
        int ret;

        if (timeout && get_timespec64(&t, timeout))
                return -EFAULT;

        if (usig && copy_from_user(&ksig, usig, sizeof(ksig)))
                return -EFAULT;

        ret = set_compat_user_sigmask(compat_ptr(ksig.sigmask), ksig.sigsetsize);
        if (ret)
                return ret;

        ret = do_io_getevents(ctx_id, min_nr, nr, events, timeout ? &t : NULL);

        interrupted = signal_pending(current);
        restore_saved_sigmask_unless(interrupted);
        if (interrupted && !ret)
                ret = -ERESTARTNOHAND;

        return ret;
}
#endif