aio.c 35.9 KB
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/*
 *	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.
 *
 *	See ../COPYING for licensing terms.
 */
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#define pr_fmt(fmt) "%s: " fmt, __func__

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#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/errno.h>
#include <linux/time.h>
#include <linux/aio_abi.h>
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#include <linux/export.h>
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#include <linux/syscalls.h>
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#include <linux/backing-dev.h>
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#include <linux/uio.h>
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#include <linux/sched.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/mm.h>
#include <linux/mman.h>
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#include <linux/mmu_context.h>
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#include <linux/slab.h>
#include <linux/timer.h>
#include <linux/aio.h>
#include <linux/highmem.h>
#include <linux/workqueue.h>
#include <linux/security.h>
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#include <linux/eventfd.h>
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#include <linux/blkdev.h>
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#include <linux/compat.h>
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#include <asm/kmap_types.h>
#include <asm/uaccess.h>

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#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;
	unsigned	tail;

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


	struct io_event		io_events[0];
}; /* 128 bytes + ring size */

#define AIO_RING_PAGES	8
struct aio_ring_info {
	unsigned long		mmap_base;
	unsigned long		mmap_size;

	struct page		**ring_pages;
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	struct mutex		ring_lock;
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	long			nr_pages;

	unsigned		nr, tail;

	struct page		*internal_pages[AIO_RING_PAGES];
};

static inline unsigned aio_ring_avail(struct aio_ring_info *info,
					struct aio_ring *ring)
{
	return (ring->head + info->nr - 1 - ring->tail) % info->nr;
}

struct kioctx {
	atomic_t		users;
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	atomic_t		dead;
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	/* This needs improving */
	unsigned long		user_id;
	struct hlist_node	list;

	wait_queue_head_t	wait;

	spinlock_t		ctx_lock;

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	atomic_t		reqs_active;
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	struct list_head	active_reqs;	/* used for cancellation */

	/* sys_io_setup currently limits this to an unsigned int */
	unsigned		max_reqs;

	struct aio_ring_info	ring_info;

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	spinlock_t		completion_lock;

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	struct rcu_head		rcu_head;
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	struct work_struct	rcu_work;
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};

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/*------ sysctl variables----*/
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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 */
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/*----end sysctl variables---*/

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static struct kmem_cache	*kiocb_cachep;
static struct kmem_cache	*kioctx_cachep;
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/* 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)
{
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	kiocb_cachep = KMEM_CACHE(kiocb, SLAB_HWCACHE_ALIGN|SLAB_PANIC);
	kioctx_cachep = KMEM_CACHE(kioctx,SLAB_HWCACHE_ALIGN|SLAB_PANIC);
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	pr_debug("sizeof(struct page) = %zu\n", sizeof(struct page));
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	return 0;
}
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__initcall(aio_setup);
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static void aio_free_ring(struct kioctx *ctx)
{
	struct aio_ring_info *info = &ctx->ring_info;
	long i;

	for (i=0; i<info->nr_pages; i++)
		put_page(info->ring_pages[i]);

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	if (info->mmap_size) {
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		vm_munmap(info->mmap_base, info->mmap_size);
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	}
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	if (info->ring_pages && info->ring_pages != info->internal_pages)
		kfree(info->ring_pages);
	info->ring_pages = NULL;
	info->nr = 0;
}

static int aio_setup_ring(struct kioctx *ctx)
{
	struct aio_ring *ring;
	struct aio_ring_info *info = &ctx->ring_info;
	unsigned nr_events = ctx->max_reqs;
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	struct mm_struct *mm = current->mm;
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	unsigned long size, populate;
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	int nr_pages;

	/* 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 = (size + PAGE_SIZE-1) >> PAGE_SHIFT;

	if (nr_pages < 0)
		return -EINVAL;

	nr_events = (PAGE_SIZE * nr_pages - sizeof(struct aio_ring)) / sizeof(struct io_event);

	info->nr = 0;
	info->ring_pages = info->internal_pages;
	if (nr_pages > AIO_RING_PAGES) {
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		info->ring_pages = kcalloc(nr_pages, sizeof(struct page *), GFP_KERNEL);
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		if (!info->ring_pages)
			return -ENOMEM;
	}

	info->mmap_size = nr_pages * PAGE_SIZE;
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	pr_debug("attempting mmap of %lu bytes\n", info->mmap_size);
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	down_write(&mm->mmap_sem);
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	info->mmap_base = do_mmap_pgoff(NULL, 0, info->mmap_size, 
					PROT_READ|PROT_WRITE,
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					MAP_ANONYMOUS|MAP_PRIVATE, 0,
					&populate);
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	if (IS_ERR((void *)info->mmap_base)) {
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		up_write(&mm->mmap_sem);
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		info->mmap_size = 0;
		aio_free_ring(ctx);
		return -EAGAIN;
	}

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	pr_debug("mmap address: 0x%08lx\n", info->mmap_base);
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	info->nr_pages = get_user_pages(current, mm, info->mmap_base, nr_pages,
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					1, 0, info->ring_pages, NULL);
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	up_write(&mm->mmap_sem);
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	if (unlikely(info->nr_pages != nr_pages)) {
		aio_free_ring(ctx);
		return -EAGAIN;
	}
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	if (populate)
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		mm_populate(info->mmap_base, populate);
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	ctx->user_id = info->mmap_base;

	info->nr = nr_events;		/* trusted copy */

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	ring = kmap_atomic(info->ring_pages[0]);
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	ring->nr = nr_events;	/* user copy */
	ring->id = ctx->user_id;
	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);
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	kunmap_atomic(ring);
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	flush_dcache_page(info->ring_pages[0]);
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	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)

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

	spin_lock_irqsave(&ctx->ctx_lock, flags);

	if (!req->ki_list.next)
		list_add(&req->ki_list, &ctx->active_reqs);

	req->ki_cancel = cancel;

	spin_unlock_irqrestore(&ctx->ctx_lock, flags);
}
EXPORT_SYMBOL(kiocb_set_cancel_fn);

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static int kiocb_cancel(struct kioctx *ctx, struct kiocb *kiocb,
			struct io_event *res)
{
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	kiocb_cancel_fn *old, *cancel;
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	int ret = -EINVAL;

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	/*
	 * Don't want to set kiocb->ki_cancel = KIOCB_CANCELLED unless it
	 * actually has a cancel function, hence the cmpxchg()
	 */

	cancel = ACCESS_ONCE(kiocb->ki_cancel);
	do {
		if (!cancel || cancel == KIOCB_CANCELLED)
			return ret;
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		old = cancel;
		cancel = cmpxchg(&kiocb->ki_cancel, old, KIOCB_CANCELLED);
	} while (cancel != old);
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	atomic_inc(&kiocb->ki_users);
	spin_unlock_irq(&ctx->ctx_lock);

	memset(res, 0, sizeof(*res));
	res->obj = (u64)(unsigned long)kiocb->ki_obj.user;
	res->data = kiocb->ki_user_data;
	ret = cancel(kiocb, res);

	spin_lock_irq(&ctx->ctx_lock);
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	return ret;
}

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static void free_ioctx_rcu(struct rcu_head *head)
{
	struct kioctx *ctx = container_of(head, struct kioctx, rcu_head);
	kmem_cache_free(kioctx_cachep, ctx);
}

/*
 * 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(struct kioctx *ctx)
{
	struct io_event res;
	struct kiocb *req;

	spin_lock_irq(&ctx->ctx_lock);

	while (!list_empty(&ctx->active_reqs)) {
		req = list_first_entry(&ctx->active_reqs,
				       struct kiocb, ki_list);

		list_del_init(&req->ki_list);
		kiocb_cancel(ctx, req, &res);
	}

	spin_unlock_irq(&ctx->ctx_lock);

	wait_event(ctx->wait, !atomic_read(&ctx->reqs_active));

	aio_free_ring(ctx);

	spin_lock(&aio_nr_lock);
	BUG_ON(aio_nr - ctx->max_reqs > aio_nr);
	aio_nr -= ctx->max_reqs;
	spin_unlock(&aio_nr_lock);

	pr_debug("freeing %p\n", ctx);

	/*
	 * Here the call_rcu() is between the wait_event() for reqs_active to
	 * hit 0, and freeing the ioctx.
	 *
	 * aio_complete() decrements reqs_active, but it has to touch the ioctx
	 * after to issue a wakeup so we use rcu.
	 */
	call_rcu(&ctx->rcu_head, free_ioctx_rcu);
}

static void put_ioctx(struct kioctx *ctx)
{
	if (unlikely(atomic_dec_and_test(&ctx->users)))
		free_ioctx(ctx);
}

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/* ioctx_alloc
 *	Allocates and initializes an ioctx.  Returns an ERR_PTR if it failed.
 */
static struct kioctx *ioctx_alloc(unsigned nr_events)
{
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	struct mm_struct *mm = current->mm;
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	struct kioctx *ctx;
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	int err = -ENOMEM;
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	/* Prevent overflows */
	if ((nr_events > (0x10000000U / sizeof(struct io_event))) ||
	    (nr_events > (0x10000000U / sizeof(struct kiocb)))) {
		pr_debug("ENOMEM: nr_events too high\n");
		return ERR_PTR(-EINVAL);
	}

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

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

	ctx->max_reqs = nr_events;

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	atomic_set(&ctx->users, 2);
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	atomic_set(&ctx->dead, 0);
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	spin_lock_init(&ctx->ctx_lock);
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	spin_lock_init(&ctx->completion_lock);
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	mutex_init(&ctx->ring_info.ring_lock);
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	init_waitqueue_head(&ctx->wait);

	INIT_LIST_HEAD(&ctx->active_reqs);

	if (aio_setup_ring(ctx) < 0)
		goto out_freectx;

	/* limit the number of system wide aios */
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	spin_lock(&aio_nr_lock);
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	if (aio_nr + nr_events > aio_max_nr ||
	    aio_nr + nr_events < aio_nr) {
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		spin_unlock(&aio_nr_lock);
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		goto out_cleanup;
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	}
	aio_nr += ctx->max_reqs;
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	spin_unlock(&aio_nr_lock);
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	/* now link into global list. */
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	spin_lock(&mm->ioctx_lock);
	hlist_add_head_rcu(&ctx->list, &mm->ioctx_list);
	spin_unlock(&mm->ioctx_lock);
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	pr_debug("allocated ioctx %p[%ld]: mm=%p mask=0x%x\n",
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		ctx, ctx->user_id, mm, ctx->ring_info.nr);
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	return ctx;

out_cleanup:
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	err = -EAGAIN;
	aio_free_ring(ctx);
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out_freectx:
	kmem_cache_free(kioctx_cachep, ctx);
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	pr_debug("error allocating ioctx %d\n", err);
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	return ERR_PTR(err);
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}

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static void kill_ioctx_work(struct work_struct *work)
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{
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	struct kioctx *ctx = container_of(work, struct kioctx, rcu_work);
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	wake_up_all(&ctx->wait);
	put_ioctx(ctx);
}
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static void kill_ioctx_rcu(struct rcu_head *head)
{
	struct kioctx *ctx = container_of(head, struct kioctx, rcu_head);
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	INIT_WORK(&ctx->rcu_work, kill_ioctx_work);
	schedule_work(&ctx->rcu_work);
}
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/* 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 void kill_ioctx(struct kioctx *ctx)
{
	if (!atomic_xchg(&ctx->dead, 1)) {
		hlist_del_rcu(&ctx->list);
		/* Between hlist_del_rcu() and dropping the initial ref */
		synchronize_rcu();
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		/*
		 * We can't punt to workqueue here because put_ioctx() ->
		 * free_ioctx() will unmap the ringbuffer, and that has to be
		 * done in the original process's context. kill_ioctx_rcu/work()
		 * exist for exit_aio(), as in that path free_ioctx() won't do
		 * the unmap.
		 */
		kill_ioctx_work(&ctx->rcu_work);
	}
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}

/* wait_on_sync_kiocb:
 *	Waits on the given sync kiocb to complete.
 */
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ssize_t wait_on_sync_kiocb(struct kiocb *iocb)
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{
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	while (atomic_read(&iocb->ki_users)) {
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		set_current_state(TASK_UNINTERRUPTIBLE);
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		if (!atomic_read(&iocb->ki_users))
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			break;
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		io_schedule();
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	}
	__set_current_state(TASK_RUNNING);
	return iocb->ki_user_data;
}
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EXPORT_SYMBOL(wait_on_sync_kiocb);
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/*
 * 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.
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 */
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void exit_aio(struct mm_struct *mm)
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{
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	struct kioctx *ctx;
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	struct hlist_node *n;
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	hlist_for_each_entry_safe(ctx, n, &mm->ioctx_list, list) {
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		if (1 != atomic_read(&ctx->users))
			printk(KERN_DEBUG
				"exit_aio:ioctx still alive: %d %d %d\n",
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				atomic_read(&ctx->users),
				atomic_read(&ctx->dead),
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				atomic_read(&ctx->reqs_active));
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		/*
		 * We don't need to bother with munmap() here -
		 * exit_mmap(mm) is coming and it'll unmap everything.
		 * Since aio_free_ring() uses non-zero ->mmap_size
		 * as indicator that it needs to unmap the area,
		 * just set it to 0; aio_free_ring() is the only
		 * place that uses ->mmap_size, so it's safe.
		 */
		ctx->ring_info.mmap_size = 0;
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		if (!atomic_xchg(&ctx->dead, 1)) {
			hlist_del_rcu(&ctx->list);
			call_rcu(&ctx->rcu_head, kill_ioctx_rcu);
		}
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	}
}

/* aio_get_req
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 *	Allocate a slot for an aio request.  Increments the ki_users count
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 * of the kioctx so that the kioctx stays around until all requests are
 * complete.  Returns NULL if no requests are free.
 *
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 * Returns with kiocb->ki_users set to 2.  The io submit code path holds
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 * an extra reference while submitting the i/o.
 * This prevents races between the aio code path referencing the
 * req (after submitting it) and aio_complete() freeing the req.
 */
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static struct kiocb *__aio_get_req(struct kioctx *ctx)
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{
	struct kiocb *req = NULL;

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

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	atomic_set(&req->ki_users, 2);
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	req->ki_ctx = ctx;

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	return req;
}

/*
 * struct kiocb's are allocated in batches to reduce the number of
 * times the ctx lock is acquired and released.
 */
#define KIOCB_BATCH_SIZE	32L
struct kiocb_batch {
	struct list_head head;
	long count; /* number of requests left to allocate */
};

static void kiocb_batch_init(struct kiocb_batch *batch, long total)
{
	INIT_LIST_HEAD(&batch->head);
	batch->count = total;
}

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static void kiocb_batch_free(struct kioctx *ctx, struct kiocb_batch *batch)
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{
	struct kiocb *req, *n;

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	if (list_empty(&batch->head))
		return;

	spin_lock_irq(&ctx->ctx_lock);
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	list_for_each_entry_safe(req, n, &batch->head, ki_batch) {
		list_del(&req->ki_batch);
		kmem_cache_free(kiocb_cachep, req);
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		atomic_dec(&ctx->reqs_active);
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	}
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	spin_unlock_irq(&ctx->ctx_lock);
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}

/*
 * Allocate a batch of kiocbs.  This avoids taking and dropping the
 * context lock a lot during setup.
 */
static int kiocb_batch_refill(struct kioctx *ctx, struct kiocb_batch *batch)
{
	unsigned short allocated, to_alloc;
	long avail;
	struct kiocb *req, *n;
	struct aio_ring *ring;

	to_alloc = min(batch->count, KIOCB_BATCH_SIZE);
	for (allocated = 0; allocated < to_alloc; allocated++) {
		req = __aio_get_req(ctx);
		if (!req)
			/* allocation failed, go with what we've got */
			break;
		list_add(&req->ki_batch, &batch->head);
	}

	if (allocated == 0)
		goto out;

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	spin_lock_irq(&ctx->ctx_lock);
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	ring = kmap_atomic(ctx->ring_info.ring_pages[0]);

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	avail = aio_ring_avail(&ctx->ring_info, ring) -
				atomic_read(&ctx->reqs_active);
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	BUG_ON(avail < 0);
	if (avail < allocated) {
		/* Trim back the number of requests. */
		list_for_each_entry_safe(req, n, &batch->head, ki_batch) {
			list_del(&req->ki_batch);
			kmem_cache_free(kiocb_cachep, req);
			if (--allocated <= avail)
				break;
		}
	}

	batch->count -= allocated;
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	atomic_add(allocated, &ctx->reqs_active);
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	kunmap_atomic(ring);
	spin_unlock_irq(&ctx->ctx_lock);
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out:
	return allocated;
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}

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static inline struct kiocb *aio_get_req(struct kioctx *ctx,
					struct kiocb_batch *batch)
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{
	struct kiocb *req;
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	if (list_empty(&batch->head))
		if (kiocb_batch_refill(ctx, batch) == 0)
			return NULL;
	req = list_first_entry(&batch->head, struct kiocb, ki_batch);
	list_del(&req->ki_batch);
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	return req;
}

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static void kiocb_free(struct kiocb *req)
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{
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	if (req->ki_filp)
		fput(req->ki_filp);
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	if (req->ki_eventfd != NULL)
		eventfd_ctx_put(req->ki_eventfd);
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	if (req->ki_dtor)
		req->ki_dtor(req);
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	if (req->ki_iovec != &req->ki_inline_vec)
		kfree(req->ki_iovec);
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	kmem_cache_free(kiocb_cachep, req);
}

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void aio_put_req(struct kiocb *req)
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{
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	if (atomic_dec_and_test(&req->ki_users))
		kiocb_free(req);
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}
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EXPORT_SYMBOL(aio_put_req);
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static struct kioctx *lookup_ioctx(unsigned long ctx_id)
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{
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	struct mm_struct *mm = current->mm;
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	struct kioctx *ctx, *ret = NULL;
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	rcu_read_lock();

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	hlist_for_each_entry_rcu(ctx, &mm->ioctx_list, list) {
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		if (ctx->user_id == ctx_id) {
			atomic_inc(&ctx->users);
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			ret = ctx;
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			break;
		}
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	}
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	rcu_read_unlock();
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	return ret;
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}

/* aio_complete
 *	Called when the io request on the given iocb is complete.
 */
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void aio_complete(struct kiocb *iocb, long res, long res2)
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{
	struct kioctx	*ctx = iocb->ki_ctx;
	struct aio_ring_info	*info;
	struct aio_ring	*ring;
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	struct io_event	*ev_page, *event;
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	unsigned long	flags;
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	unsigned tail, pos;
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	/*
	 * Special case handling for sync iocbs:
	 *  - events go directly into the iocb for fast handling
	 *  - the sync task with the iocb in its stack holds the single iocb
	 *    ref, no other paths have a way to get another ref
	 *  - the sync task helpfully left a reference to itself in the iocb
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	 */
	if (is_sync_kiocb(iocb)) {
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		BUG_ON(atomic_read(&iocb->ki_users) != 1);
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		iocb->ki_user_data = res;
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		atomic_set(&iocb->ki_users, 0);
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		wake_up_process(iocb->ki_obj.tsk);
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		return;
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	}

	info = &ctx->ring_info;

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	/*
	 * Take rcu_read_lock() in case the kioctx is being destroyed, as we
	 * need to issue a wakeup after decrementing reqs_active.
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	 */
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	rcu_read_lock();
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	if (iocb->ki_list.next) {
		unsigned long flags;

		spin_lock_irqsave(&ctx->ctx_lock, flags);
		list_del(&iocb->ki_list);
		spin_unlock_irqrestore(&ctx->ctx_lock, flags);
	}
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	/*
	 * cancelled requests don't get events, userland was given one
	 * when the event got cancelled.
	 */
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	if (unlikely(xchg(&iocb->ki_cancel,
			  KIOCB_CANCELLED) == KIOCB_CANCELLED))
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		goto put_rq;

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	/*
	 * Add a completion event to the ring buffer. Must be done holding
	 * ctx->ctx_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);

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

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	if (++tail >= info->nr)
		tail = 0;
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	ev_page = kmap_atomic(info->ring_pages[pos / AIO_EVENTS_PER_PAGE]);
	event = ev_page + pos % AIO_EVENTS_PER_PAGE;

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	event->obj = (u64)(unsigned long)iocb->ki_obj.user;
	event->data = iocb->ki_user_data;
	event->res = res;
	event->res2 = res2;

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

	pr_debug("%p[%u]: %p: %p %Lx %lx %lx\n",
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		 ctx, tail, iocb, iocb->ki_obj.user, iocb->ki_user_data,
		 res, res2);
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	/* after flagging the request as done, we
	 * must never even look at it again
	 */
	smp_wmb();	/* make event visible before updating tail */

	info->tail = tail;

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	ring = kmap_atomic(info->ring_pages[0]);
	ring->tail = tail;
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	kunmap_atomic(ring);
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	flush_dcache_page(info->ring_pages[0]);
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	spin_unlock_irqrestore(&ctx->completion_lock, flags);

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	pr_debug("added to ring %p at [%u]\n", iocb, tail);
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	/*
	 * 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.
	 */
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	if (iocb->ki_eventfd != NULL)
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		eventfd_signal(iocb->ki_eventfd, 1);

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put_rq:
	/* everything turned out well, dispose of the aiocb. */
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	aio_put_req(iocb);
	atomic_dec(&ctx->reqs_active);
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	/*
	 * 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();

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

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	rcu_read_unlock();
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}
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EXPORT_SYMBOL(aio_complete);
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/* aio_read_events
 *	Pull an event off of the ioctx's event ring.  Returns the number of
 *	events fetched
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 */
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static long aio_read_events_ring(struct kioctx *ctx,
				 struct io_event __user *event, long nr)
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{
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	struct aio_ring_info *info = &ctx->ring_info;
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	struct aio_ring *ring;
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	unsigned head, pos;
	long ret = 0;
	int copy_ret;

	mutex_lock(&info->ring_lock);
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	ring = kmap_atomic(info->ring_pages[0]);
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	head = ring->head;
	kunmap_atomic(ring);

	pr_debug("h%u t%u m%u\n", head, info->tail, info->nr);
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	if (head == info->tail)
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		goto out;

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

		avail = (head <= info->tail ? info->tail : info->nr) - head;
		if (head == info->tail)
			break;

		avail = min(avail, nr - ret);
		avail = min_t(long, avail, AIO_EVENTS_PER_PAGE -
			    ((head + AIO_EVENTS_OFFSET) % AIO_EVENTS_PER_PAGE));

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

		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 %= info->nr;
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	}

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	ring = kmap_atomic(info->ring_pages[0]);
	ring->head = head;
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	kunmap_atomic(ring);
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	flush_dcache_page(info->ring_pages[0]);
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	pr_debug("%li  h%u t%u\n", ret, head, info->tail);
out:
	mutex_unlock(&info->ring_lock);

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	return ret;
}

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static bool aio_read_events(struct kioctx *ctx, long min_nr, long nr,
			    struct io_event __user *event, long *i)
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{
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	long ret = aio_read_events_ring(ctx, event + *i, nr - *i);
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	if (ret > 0)
		*i += ret;
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	if (unlikely(atomic_read(&ctx->dead)))
		ret = -EINVAL;
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	if (!*i)
		*i = ret;
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	return ret < 0 || *i >= min_nr;
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}

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static long read_events(struct kioctx *ctx, long min_nr, long nr,
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			struct io_event __user *event,
			struct timespec __user *timeout)
{
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	ktime_t until = { .tv64 = KTIME_MAX };
	long ret = 0;
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	if (timeout) {
		struct timespec	ts;
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		if (unlikely(copy_from_user(&ts, timeout, sizeof(ts))))
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			return -EFAULT;
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		until = timespec_to_ktime(ts);
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	}

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	/*
	 * 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.
	 */
	wait_event_interruptible_hrtimeout(ctx->wait,
			aio_read_events(ctx, min_nr, nr, event, &ret), until);
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	if (!ret && signal_pending(current))
		ret = -EINTR;
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	return ret;
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}

/* 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.
 */
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SYSCALL_DEFINE2(io_setup, unsigned, nr_events, aio_context_t __user *, ctxp)
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{
	struct kioctx *ioctx = NULL;
	unsigned long ctx;
	long ret;

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

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

	ioctx = ioctx_alloc(nr_events);
	ret = PTR_ERR(ioctx);
	if (!IS_ERR(ioctx)) {
		ret = put_user(ioctx->user_id, ctxp);
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		if (ret)
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			kill_ioctx(ioctx);
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		put_ioctx(ioctx);
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	}

out:
	return ret;
}

/* sys_io_destroy:
 *	Destroy the aio_context specified.  May cancel any outstanding 
 *	AIOs and block on completion.  Will fail with -ENOSYS if not
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 *	implemented.  May fail with -EINVAL if the context pointed to
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 *	is invalid.
 */
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SYSCALL_DEFINE1(io_destroy, aio_context_t, ctx)
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{
	struct kioctx *ioctx = lookup_ioctx(ctx);
	if (likely(NULL != ioctx)) {
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		kill_ioctx(ioctx);
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		put_ioctx(ioctx);
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		return 0;
	}
	pr_debug("EINVAL: io_destroy: invalid context id\n");
	return -EINVAL;
}

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static void aio_advance_iovec(struct kiocb *iocb, ssize_t ret)
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{
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	struct iovec *iov = &iocb->ki_iovec[iocb->ki_cur_seg];

	BUG_ON(ret <= 0);

	while (iocb->ki_cur_seg < iocb->ki_nr_segs && ret > 0) {
		ssize_t this = min((ssize_t)iov->iov_len, ret);
		iov->iov_base += this;
		iov->iov_len -= this;
		iocb->ki_left -= this;
		ret -= this;
		if (iov->iov_len == 0) {
			iocb->ki_cur_seg++;
			iov++;
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		}
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	}
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	/* the caller should not have done more io than what fit in
	 * the remaining iovecs */
	BUG_ON(ret > 0 && iocb->ki_left == 0);
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}

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static ssize_t aio_rw_vect_retry(struct kiocb *iocb)
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{
	struct file *file = iocb->ki_filp;
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	struct address_space *mapping = file->f_mapping;
	struct inode *inode = mapping->host;
	ssize_t (*rw_op)(struct kiocb *, const struct iovec *,
			 unsigned long, loff_t);
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	ssize_t ret = 0;
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	unsigned short opcode;

	if ((iocb->ki_opcode == IOCB_CMD_PREADV) ||
		(iocb->ki_opcode == IOCB_CMD_PREAD)) {
		rw_op = file->f_op->aio_read;
		opcode = IOCB_CMD_PREADV;
	} else {
		rw_op = file->f_op->aio_write;
		opcode = IOCB_CMD_PWRITEV;
	}
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	/* This matches the pread()/pwrite() logic */
	if (iocb->ki_pos < 0)
		return -EINVAL;

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	if (opcode == IOCB_CMD_PWRITEV)
		file_start_write(file);
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	do {
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		ret = rw_op(iocb, &iocb->ki_iovec[iocb->ki_cur_seg],
			    iocb->ki_nr_segs - iocb->ki_cur_seg,
			    iocb->ki_pos);
		if (ret > 0)
			aio_advance_iovec(iocb, ret);

	/* retry all partial writes.  retry partial reads as long as its a
	 * regular file. */
	} while (ret > 0 && iocb->ki_left > 0 &&
		 (opcode == IOCB_CMD_PWRITEV ||
		  (!S_ISFIFO(inode->i_mode) && !S_ISSOCK(inode->i_mode))));
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	if (opcode == IOCB_CMD_PWRITEV)
		file_end_write(file);
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	/* This means we must have transferred all that we could */
	/* No need to retry anymore */
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	if ((ret == 0) || (iocb->ki_left == 0))
		ret = iocb->ki_nbytes - iocb->ki_left;

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	/* If we managed to write some out we return that, rather than
	 * the eventual error. */
	if (opcode == IOCB_CMD_PWRITEV
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	    && ret < 0 && ret != -EIOCBQUEUED
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	    && iocb->ki_nbytes - iocb->ki_left)
		ret = iocb->ki_nbytes - iocb->ki_left;

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	return ret;
}

static ssize_t aio_fdsync(struct kiocb *iocb)
{
	struct file *file = iocb->ki_filp;
	ssize_t ret = -EINVAL;

	if (file->f_op->aio_fsync)
		ret = file->f_op->aio_fsync(iocb, 1);
	return ret;
}

static ssize_t aio_fsync(struct kiocb *iocb)
{
	struct file *file = iocb->ki_filp;
	ssize_t ret = -EINVAL;

	if (file->f_op->aio_fsync)
		ret = file->f_op->aio_fsync(iocb, 0);
	return ret;
}

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static ssize_t aio_setup_vectored_rw(int type, struct kiocb *kiocb, bool compat)
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{
	ssize_t ret;

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#ifdef CONFIG_COMPAT
	if (compat)
		ret = compat_rw_copy_check_uvector(type,
				(struct compat_iovec __user *)kiocb->ki_buf,
				kiocb->ki_nbytes, 1, &kiocb->ki_inline_vec,
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				&kiocb->ki_iovec);
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	else
#endif
		ret = rw_copy_check_uvector(type,
				(struct iovec __user *)kiocb->ki_buf,
				kiocb->ki_nbytes, 1, &kiocb->ki_inline_vec,
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				&kiocb->ki_iovec);
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	if (ret < 0)
		goto out;

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	ret = rw_verify_area(type, kiocb->ki_filp, &kiocb->ki_pos, ret);
	if (ret < 0)
		goto out;

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	kiocb->ki_nr_segs = kiocb->ki_nbytes;
	kiocb->ki_cur_seg = 0;
	/* ki_nbytes/left now reflect bytes instead of segs */
	kiocb->ki_nbytes = ret;
	kiocb->ki_left = ret;

	ret = 0;
out:
	return ret;
}

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static ssize_t aio_setup_single_vector(int type, struct file * file, struct kiocb *kiocb)
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{
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	int bytes;

	bytes = rw_verify_area(type, file, &kiocb->ki_pos, kiocb->ki_left);
	if (bytes < 0)
		return bytes;

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	kiocb->ki_iovec = &kiocb->ki_inline_vec;
	kiocb->ki_iovec->iov_base = kiocb->ki_buf;
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	kiocb->ki_iovec->iov_len = bytes;
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	kiocb->ki_nr_segs = 1;
	kiocb->ki_cur_seg = 0;
	return 0;
}

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/*
 * aio_setup_iocb:
 *	Performs the initial checks and aio retry method
 *	setup for the kiocb at the time of io submission.
 */
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static ssize_t aio_setup_iocb(struct kiocb *kiocb, bool compat)
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{
	struct file *file = kiocb->ki_filp;
	ssize_t ret = 0;

	switch (kiocb->ki_opcode) {
	case IOCB_CMD_PREAD:
		ret = -EBADF;
		if (unlikely(!(file->f_mode & FMODE_READ)))
			break;
		ret = -EFAULT;
		if (unlikely(!access_ok(VERIFY_WRITE, kiocb->ki_buf,
			kiocb->ki_left)))
			break;
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		ret = aio_setup_single_vector(READ, file, kiocb);
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		if (ret)
			break;
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		ret = -EINVAL;
		if (file->f_op->aio_read)
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			kiocb->ki_retry = aio_rw_vect_retry;
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		break;
	case IOCB_CMD_PWRITE:
		ret = -EBADF;
		if (unlikely(!(file->f_mode & FMODE_WRITE)))
			break;
		ret = -EFAULT;
		if (unlikely(!access_ok(VERIFY_READ, kiocb->ki_buf,
			kiocb->ki_left)))
			break;
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		ret = aio_setup_single_vector(WRITE, file, kiocb);
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		if (ret)
			break;
		ret = -EINVAL;
		if (file->f_op->aio_write)
			kiocb->ki_retry = aio_rw_vect_retry;
		break;
	case IOCB_CMD_PREADV:
		ret = -EBADF;
		if (unlikely(!(file->f_mode & FMODE_READ)))
			break;
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		ret = aio_setup_vectored_rw(READ, kiocb, compat);
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		if (ret)
			break;
		ret = -EINVAL;
		if (file->f_op->aio_read)
			kiocb->ki_retry = aio_rw_vect_retry;
		break;
	case IOCB_CMD_PWRITEV:
		ret = -EBADF;
		if (unlikely(!(file->f_mode & FMODE_WRITE)))
			break;
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		ret = aio_setup_vectored_rw(WRITE, kiocb, compat);
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		if (ret)
			break;
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		ret = -EINVAL;
		if (file->f_op->aio_write)
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			kiocb->ki_retry = aio_rw_vect_retry;
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		break;
	case IOCB_CMD_FDSYNC:
		ret = -EINVAL;
		if (file->f_op->aio_fsync)
			kiocb->ki_retry = aio_fdsync;
		break;
	case IOCB_CMD_FSYNC:
		ret = -EINVAL;
		if (file->f_op->aio_fsync)
			kiocb->ki_retry = aio_fsync;
		break;
	default:
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		pr_debug("EINVAL: no operation provided\n");
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		ret = -EINVAL;
	}

	if (!kiocb->ki_retry)
		return ret;

	return 0;
}

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static int io_submit_one(struct kioctx *ctx, struct iocb __user *user_iocb,
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			 struct iocb *iocb, struct kiocb_batch *batch,
			 bool compat)
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{
	struct kiocb *req;
	ssize_t ret;

	/* enforce forwards compatibility on users */
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	if (unlikely(iocb->aio_reserved1 || iocb->aio_reserved2)) {
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		pr_debug("EINVAL: reserve field set\n");
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		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: io_submit: overflow check\n");
		return -EINVAL;
	}

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	req = aio_get_req(ctx, batch);  /* returns with 2 references to req */
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	if (unlikely(!req))
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		return -EAGAIN;
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	req->ki_filp = fget(iocb->aio_fildes);
	if (unlikely(!req->ki_filp)) {
		ret = -EBADF;
		goto out_put_req;
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	}
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	if (iocb->aio_flags & IOCB_FLAG_RESFD) {
		/*
		 * 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.
		 */
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		req->ki_eventfd = eventfd_ctx_fdget((int) iocb->aio_resfd);
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		if (IS_ERR(req->ki_eventfd)) {
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			ret = PTR_ERR(req->ki_eventfd);
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			req->ki_eventfd = NULL;
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			goto out_put_req;
		}
	}
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	ret = put_user(req->ki_key, &user_iocb->aio_key);
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	if (unlikely(ret)) {
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		pr_debug("EFAULT: aio_key\n");
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		goto out_put_req;
	}

	req->ki_obj.user = user_iocb;
	req->ki_user_data = iocb->aio_data;
	req->ki_pos = iocb->aio_offset;

	req->ki_buf = (char __user *)(unsigned long)iocb->aio_buf;
	req->ki_left = req->ki_nbytes = iocb->aio_nbytes;
	req->ki_opcode = iocb->aio_lio_opcode;

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	ret = aio_setup_iocb(req, compat);
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	if (ret)
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		goto out_put_req;
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	ret = req->ki_retry(req);
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	if (ret != -EIOCBQUEUED) {
		/*
		 * There's no easy way to restart the syscall since other AIO's
		 * may be already running. Just fail this IO with EINTR.
		 */
		if (unlikely(ret == -ERESTARTSYS || ret == -ERESTARTNOINTR ||
			     ret == -ERESTARTNOHAND ||
			     ret == -ERESTART_RESTARTBLOCK))
			ret = -EINTR;
		aio_complete(req, ret, 0);
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	}
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	aio_put_req(req);	/* drop extra ref to req */
	return 0;

out_put_req:
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	atomic_dec(&ctx->reqs_active);
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	aio_put_req(req);	/* drop extra ref to req */
	aio_put_req(req);	/* drop i/o ref to req */
	return ret;
}

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long do_io_submit(aio_context_t ctx_id, long nr,
		  struct iocb __user *__user *iocbpp, bool compat)
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{
	struct kioctx *ctx;
	long ret = 0;
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	int i = 0;
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	struct blk_plug plug;
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	struct kiocb_batch batch;
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	if (unlikely(nr < 0))
		return -EINVAL;

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	if (unlikely(nr > LONG_MAX/sizeof(*iocbpp)))
		nr = LONG_MAX/sizeof(*iocbpp);

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	if (unlikely(!access_ok(VERIFY_READ, iocbpp, (nr*sizeof(*iocbpp)))))
		return -EFAULT;

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

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	kiocb_batch_init(&batch, nr);

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	blk_start_plug(&plug);

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