Merge tag 'hwmon-for-v6.13-rc7' of git://git.kernel.org/pub/scm/linux/kernel/git...

[linux.git] / fs / iomap / direct-io.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2010 Red Hat, Inc.
 * Copyright (c) 2016-2021 Christoph Hellwig.
 */
#include <linux/module.h>
#include <linux/compiler.h>
#include <linux/fs.h>
#include <linux/fscrypt.h>
#include <linux/pagemap.h>
#include <linux/iomap.h>
#include <linux/backing-dev.h>
#include <linux/uio.h>
#include <linux/task_io_accounting_ops.h>
#include "trace.h"

#include "../internal.h"

/*
 * Private flags for iomap_dio, must not overlap with the public ones in
 * iomap.h:
 */
#define IOMAP_DIO_CALLER_COMP   (1U << 26)
#define IOMAP_DIO_INLINE_COMP   (1U << 27)
#define IOMAP_DIO_WRITE_THROUGH (1U << 28)
#define IOMAP_DIO_NEED_SYNC     (1U << 29)
#define IOMAP_DIO_WRITE         (1U << 30)
#define IOMAP_DIO_DIRTY         (1U << 31)

/*
 * Used for sub block zeroing in iomap_dio_zero()
 */
#define IOMAP_ZERO_PAGE_SIZE (SZ_64K)
#define IOMAP_ZERO_PAGE_ORDER (get_order(IOMAP_ZERO_PAGE_SIZE))
static struct page *zero_page;

struct iomap_dio {
        struct kiocb            *iocb;
        const struct iomap_dio_ops *dops;
        loff_t                  i_size;
        loff_t                  size;
        atomic_t                ref;
        unsigned                flags;
        int                     error;
        size_t                  done_before;
        bool                    wait_for_completion;

        union {
                /* used during submission and for synchronous completion: */
                struct {
                        struct iov_iter         *iter;
                        struct task_struct      *waiter;
                } submit;

                /* used for aio completion: */
                struct {
                        struct work_struct      work;
                } aio;
        };
};

static struct bio *iomap_dio_alloc_bio(const struct iomap_iter *iter,
                struct iomap_dio *dio, unsigned short nr_vecs, blk_opf_t opf)
{
        if (dio->dops && dio->dops->bio_set)
                return bio_alloc_bioset(iter->iomap.bdev, nr_vecs, opf,
                                        GFP_KERNEL, dio->dops->bio_set);
        return bio_alloc(iter->iomap.bdev, nr_vecs, opf, GFP_KERNEL);
}

static void iomap_dio_submit_bio(const struct iomap_iter *iter,
                struct iomap_dio *dio, struct bio *bio, loff_t pos)
{
        struct kiocb *iocb = dio->iocb;

        atomic_inc(&dio->ref);

        /* Sync dio can't be polled reliably */
        if ((iocb->ki_flags & IOCB_HIPRI) && !is_sync_kiocb(iocb)) {
                bio_set_polled(bio, iocb);
                WRITE_ONCE(iocb->private, bio);
        }

        if (dio->dops && dio->dops->submit_io)
                dio->dops->submit_io(iter, bio, pos);
        else
                submit_bio(bio);
}

ssize_t iomap_dio_complete(struct iomap_dio *dio)
{
        const struct iomap_dio_ops *dops = dio->dops;
        struct kiocb *iocb = dio->iocb;
        loff_t offset = iocb->ki_pos;
        ssize_t ret = dio->error;

        if (dops && dops->end_io)
                ret = dops->end_io(iocb, dio->size, ret, dio->flags);

        if (likely(!ret)) {
                ret = dio->size;
                /* check for short read */
                if (offset + ret > dio->i_size &&
                    !(dio->flags & IOMAP_DIO_WRITE))
                        ret = dio->i_size - offset;
        }

        /*
         * Try again to invalidate clean pages which might have been cached by
         * non-direct readahead, or faulted in by get_user_pages() if the source
         * of the write was an mmap'ed region of the file we're writing.  Either
         * one is a pretty crazy thing to do, so we don't support it 100%.  If
         * this invalidation fails, tough, the write still worked...
         *
         * And this page cache invalidation has to be after ->end_io(), as some
         * filesystems convert unwritten extents to real allocations in
         * ->end_io() when necessary, otherwise a racing buffer read would cache
         * zeros from unwritten extents.
         */
        if (!dio->error && dio->size && (dio->flags & IOMAP_DIO_WRITE))
                kiocb_invalidate_post_direct_write(iocb, dio->size);

        inode_dio_end(file_inode(iocb->ki_filp));

        if (ret > 0) {
                iocb->ki_pos += ret;

                /*
                 * If this is a DSYNC write, make sure we push it to stable
                 * storage now that we've written data.
                 */
                if (dio->flags & IOMAP_DIO_NEED_SYNC)
                        ret = generic_write_sync(iocb, ret);
                if (ret > 0)
                        ret += dio->done_before;
        }
        trace_iomap_dio_complete(iocb, dio->error, ret);
        kfree(dio);
        return ret;
}
EXPORT_SYMBOL_GPL(iomap_dio_complete);

static ssize_t iomap_dio_deferred_complete(void *data)
{
        return iomap_dio_complete(data);
}

static void iomap_dio_complete_work(struct work_struct *work)
{
        struct iomap_dio *dio = container_of(work, struct iomap_dio, aio.work);
        struct kiocb *iocb = dio->iocb;

        iocb->ki_complete(iocb, iomap_dio_complete(dio));
}

/*
 * Set an error in the dio if none is set yet.  We have to use cmpxchg
 * as the submission context and the completion context(s) can race to
 * update the error.
 */
static inline void iomap_dio_set_error(struct iomap_dio *dio, int ret)
{
        cmpxchg(&dio->error, 0, ret);
}

void iomap_dio_bio_end_io(struct bio *bio)
{
        struct iomap_dio *dio = bio->bi_private;
        bool should_dirty = (dio->flags & IOMAP_DIO_DIRTY);
        struct kiocb *iocb = dio->iocb;

        if (bio->bi_status)
                iomap_dio_set_error(dio, blk_status_to_errno(bio->bi_status));
        if (!atomic_dec_and_test(&dio->ref))
                goto release_bio;

        /*
         * Synchronous dio, task itself will handle any completion work
         * that needs after IO. All we need to do is wake the task.
         */
        if (dio->wait_for_completion) {
                struct task_struct *waiter = dio->submit.waiter;

                WRITE_ONCE(dio->submit.waiter, NULL);
                blk_wake_io_task(waiter);
                goto release_bio;
        }

        /*
         * Flagged with IOMAP_DIO_INLINE_COMP, we can complete it inline
         */
        if (dio->flags & IOMAP_DIO_INLINE_COMP) {
                WRITE_ONCE(iocb->private, NULL);
                iomap_dio_complete_work(&dio->aio.work);
                goto release_bio;
        }

        /*
         * If this dio is flagged with IOMAP_DIO_CALLER_COMP, then schedule
         * our completion that way to avoid an async punt to a workqueue.
         */
        if (dio->flags & IOMAP_DIO_CALLER_COMP) {
                /* only polled IO cares about private cleared */
                iocb->private = dio;
                iocb->dio_complete = iomap_dio_deferred_complete;

                /*
                 * Invoke ->ki_complete() directly. We've assigned our
                 * dio_complete callback handler, and since the issuer set
                 * IOCB_DIO_CALLER_COMP, we know their ki_complete handler will
                 * notice ->dio_complete being set and will defer calling that
                 * handler until it can be done from a safe task context.
                 *
                 * Note that the 'res' being passed in here is not important
                 * for this case. The actual completion value of the request
                 * will be gotten from dio_complete when that is run by the
                 * issuer.
                 */
                iocb->ki_complete(iocb, 0);
                goto release_bio;
        }

        /*
         * Async DIO completion that requires filesystem level completion work
         * gets punted to a work queue to complete as the operation may require
         * more IO to be issued to finalise filesystem metadata changes or
         * guarantee data integrity.
         */
        INIT_WORK(&dio->aio.work, iomap_dio_complete_work);
        queue_work(file_inode(iocb->ki_filp)->i_sb->s_dio_done_wq,
                        &dio->aio.work);
release_bio:
        if (should_dirty) {
                bio_check_pages_dirty(bio);
        } else {
                bio_release_pages(bio, false);
                bio_put(bio);
        }
}
EXPORT_SYMBOL_GPL(iomap_dio_bio_end_io);

static int iomap_dio_zero(const struct iomap_iter *iter, struct iomap_dio *dio,
                loff_t pos, unsigned len)
{
        struct inode *inode = file_inode(dio->iocb->ki_filp);
        struct bio *bio;

        if (!len)
                return 0;
        /*
         * Max block size supported is 64k
         */
        if (WARN_ON_ONCE(len > IOMAP_ZERO_PAGE_SIZE))
                return -EINVAL;

        bio = iomap_dio_alloc_bio(iter, dio, 1, REQ_OP_WRITE | REQ_SYNC | REQ_IDLE);
        fscrypt_set_bio_crypt_ctx(bio, inode, pos >> inode->i_blkbits,
                                  GFP_KERNEL);
        bio->bi_iter.bi_sector = iomap_sector(&iter->iomap, pos);
        bio->bi_private = dio;
        bio->bi_end_io = iomap_dio_bio_end_io;

        __bio_add_page(bio, zero_page, len, 0);
        iomap_dio_submit_bio(iter, dio, bio, pos);
        return 0;
}

/*
 * Figure out the bio's operation flags from the dio request, the
 * mapping, and whether or not we want FUA.  Note that we can end up
 * clearing the WRITE_THROUGH flag in the dio request.
 */
static inline blk_opf_t iomap_dio_bio_opflags(struct iomap_dio *dio,
                const struct iomap *iomap, bool use_fua, bool atomic)
{
        blk_opf_t opflags = REQ_SYNC | REQ_IDLE;

        if (!(dio->flags & IOMAP_DIO_WRITE))
                return REQ_OP_READ;

        opflags |= REQ_OP_WRITE;
        if (use_fua)
                opflags |= REQ_FUA;
        else
                dio->flags &= ~IOMAP_DIO_WRITE_THROUGH;
        if (atomic)
                opflags |= REQ_ATOMIC;

        return opflags;
}

static loff_t iomap_dio_bio_iter(const struct iomap_iter *iter,
                struct iomap_dio *dio)
{
        const struct iomap *iomap = &iter->iomap;
        struct inode *inode = iter->inode;
        unsigned int fs_block_size = i_blocksize(inode), pad;
        const loff_t length = iomap_length(iter);
        bool atomic = iter->flags & IOMAP_ATOMIC;
        loff_t pos = iter->pos;
        blk_opf_t bio_opf;
        struct bio *bio;
        bool need_zeroout = false;
        bool use_fua = false;
        int nr_pages, ret = 0;
        size_t copied = 0;
        size_t orig_count;

        if (atomic && length != fs_block_size)
                return -EINVAL;

        if ((pos | length) & (bdev_logical_block_size(iomap->bdev) - 1) ||
            !bdev_iter_is_aligned(iomap->bdev, dio->submit.iter))
                return -EINVAL;

        if (iomap->type == IOMAP_UNWRITTEN) {
                dio->flags |= IOMAP_DIO_UNWRITTEN;
                need_zeroout = true;
        }

        if (iomap->flags & IOMAP_F_SHARED)
                dio->flags |= IOMAP_DIO_COW;

        if (iomap->flags & IOMAP_F_NEW) {
                need_zeroout = true;
        } else if (iomap->type == IOMAP_MAPPED) {
                /*
                 * Use a FUA write if we need datasync semantics, this is a pure
                 * data IO that doesn't require any metadata updates (including
                 * after IO completion such as unwritten extent conversion) and
                 * the underlying device either supports FUA or doesn't have
                 * a volatile write cache. This allows us to avoid cache flushes
                 * on IO completion. If we can't use writethrough and need to
                 * sync, disable in-task completions as dio completion will
                 * need to call generic_write_sync() which will do a blocking
                 * fsync / cache flush call.
                 */
                if (!(iomap->flags & (IOMAP_F_SHARED|IOMAP_F_DIRTY)) &&
                    (dio->flags & IOMAP_DIO_WRITE_THROUGH) &&
                    (bdev_fua(iomap->bdev) || !bdev_write_cache(iomap->bdev)))
                        use_fua = true;
                else if (dio->flags & IOMAP_DIO_NEED_SYNC)
                        dio->flags &= ~IOMAP_DIO_CALLER_COMP;
        }

        /*
         * Save the original count and trim the iter to just the extent we
         * are operating on right now.  The iter will be re-expanded once
         * we are done.
         */
        orig_count = iov_iter_count(dio->submit.iter);
        iov_iter_truncate(dio->submit.iter, length);

        if (!iov_iter_count(dio->submit.iter))
                goto out;

        /*
         * We can only do deferred completion for pure overwrites that
         * don't require additional IO at completion. This rules out
         * writes that need zeroing or extent conversion, extend
         * the file size, or issue journal IO or cache flushes
         * during completion processing.
         */
        if (need_zeroout ||
            ((dio->flags & IOMAP_DIO_NEED_SYNC) && !use_fua) ||
            ((dio->flags & IOMAP_DIO_WRITE) && pos >= i_size_read(inode)))
                dio->flags &= ~IOMAP_DIO_CALLER_COMP;

        /*
         * The rules for polled IO completions follow the guidelines as the
         * ones we set for inline and deferred completions. If none of those
         * are available for this IO, clear the polled flag.
         */
        if (!(dio->flags & (IOMAP_DIO_INLINE_COMP|IOMAP_DIO_CALLER_COMP)))
                dio->iocb->ki_flags &= ~IOCB_HIPRI;

        if (need_zeroout) {
                /* zero out from the start of the block to the write offset */
                pad = pos & (fs_block_size - 1);

                ret = iomap_dio_zero(iter, dio, pos - pad, pad);
                if (ret)
                        goto out;
        }

        bio_opf = iomap_dio_bio_opflags(dio, iomap, use_fua, atomic);

        nr_pages = bio_iov_vecs_to_alloc(dio->submit.iter, BIO_MAX_VECS);
        do {
                size_t n;
                if (dio->error) {
                        iov_iter_revert(dio->submit.iter, copied);
                        copied = ret = 0;
                        goto out;
                }

                bio = iomap_dio_alloc_bio(iter, dio, nr_pages, bio_opf);
                fscrypt_set_bio_crypt_ctx(bio, inode, pos >> inode->i_blkbits,
                                          GFP_KERNEL);
                bio->bi_iter.bi_sector = iomap_sector(iomap, pos);
                bio->bi_write_hint = inode->i_write_hint;
                bio->bi_ioprio = dio->iocb->ki_ioprio;
                bio->bi_private = dio;
                bio->bi_end_io = iomap_dio_bio_end_io;

                ret = bio_iov_iter_get_pages(bio, dio->submit.iter);
                if (unlikely(ret)) {
                        /*
                         * We have to stop part way through an IO. We must fall
                         * through to the sub-block tail zeroing here, otherwise
                         * this short IO may expose stale data in the tail of
                         * the block we haven't written data to.
                         */
                        bio_put(bio);
                        goto zero_tail;
                }

                n = bio->bi_iter.bi_size;
                if (WARN_ON_ONCE(atomic && n != length)) {
                        /*
                         * This bio should have covered the complete length,
                         * which it doesn't, so error. We may need to zero out
                         * the tail (complete FS block), similar to when
                         * bio_iov_iter_get_pages() returns an error, above.
                         */
                        ret = -EINVAL;
                        bio_put(bio);
                        goto zero_tail;
                }
                if (dio->flags & IOMAP_DIO_WRITE) {
                        task_io_account_write(n);
                } else {
                        if (dio->flags & IOMAP_DIO_DIRTY)
                                bio_set_pages_dirty(bio);
                }

                dio->size += n;
                copied += n;

                nr_pages = bio_iov_vecs_to_alloc(dio->submit.iter,
                                                 BIO_MAX_VECS);
                /*
                 * We can only poll for single bio I/Os.
                 */
                if (nr_pages)
                        dio->iocb->ki_flags &= ~IOCB_HIPRI;
                iomap_dio_submit_bio(iter, dio, bio, pos);
                pos += n;
        } while (nr_pages);

        /*
         * We need to zeroout the tail of a sub-block write if the extent type
         * requires zeroing or the write extends beyond EOF. If we don't zero
         * the block tail in the latter case, we can expose stale data via mmap
         * reads of the EOF block.
         */
zero_tail:
        if (need_zeroout ||
            ((dio->flags & IOMAP_DIO_WRITE) && pos >= i_size_read(inode))) {
                /* zero out from the end of the write to the end of the block */
                pad = pos & (fs_block_size - 1);
                if (pad)
                        ret = iomap_dio_zero(iter, dio, pos,
                                             fs_block_size - pad);
        }
out:
        /* Undo iter limitation to current extent */
        iov_iter_reexpand(dio->submit.iter, orig_count - copied);
        if (copied)
                return copied;
        return ret;
}

static loff_t iomap_dio_hole_iter(const struct iomap_iter *iter,
                struct iomap_dio *dio)
{
        loff_t length = iov_iter_zero(iomap_length(iter), dio->submit.iter);

        dio->size += length;
        if (!length)
                return -EFAULT;
        return length;
}

static loff_t iomap_dio_inline_iter(const struct iomap_iter *iomi,
                struct iomap_dio *dio)
{
        const struct iomap *iomap = &iomi->iomap;
        struct iov_iter *iter = dio->submit.iter;
        void *inline_data = iomap_inline_data(iomap, iomi->pos);
        loff_t length = iomap_length(iomi);
        loff_t pos = iomi->pos;
        size_t copied;

        if (WARN_ON_ONCE(!iomap_inline_data_valid(iomap)))
                return -EIO;

        if (dio->flags & IOMAP_DIO_WRITE) {
                loff_t size = iomi->inode->i_size;

                if (pos > size)
                        memset(iomap_inline_data(iomap, size), 0, pos - size);
                copied = copy_from_iter(inline_data, length, iter);
                if (copied) {
                        if (pos + copied > size)
                                i_size_write(iomi->inode, pos + copied);
                        mark_inode_dirty(iomi->inode);
                }
        } else {
                copied = copy_to_iter(inline_data, length, iter);
        }
        dio->size += copied;
        if (!copied)
                return -EFAULT;
        return copied;
}

static loff_t iomap_dio_iter(const struct iomap_iter *iter,
                struct iomap_dio *dio)
{
        switch (iter->iomap.type) {
        case IOMAP_HOLE:
                if (WARN_ON_ONCE(dio->flags & IOMAP_DIO_WRITE))
                        return -EIO;
                return iomap_dio_hole_iter(iter, dio);
        case IOMAP_UNWRITTEN:
                if (!(dio->flags & IOMAP_DIO_WRITE))
                        return iomap_dio_hole_iter(iter, dio);
                return iomap_dio_bio_iter(iter, dio);
        case IOMAP_MAPPED:
                return iomap_dio_bio_iter(iter, dio);
        case IOMAP_INLINE:
                return iomap_dio_inline_iter(iter, dio);
        case IOMAP_DELALLOC:
                /*
                 * DIO is not serialised against mmap() access at all, and so
                 * if the page_mkwrite occurs between the writeback and the
                 * iomap_iter() call in the DIO path, then it will see the
                 * DELALLOC block that the page-mkwrite allocated.
                 */
                pr_warn_ratelimited("Direct I/O collision with buffered writes! File: %pD4 Comm: %.20s\n",
                                    dio->iocb->ki_filp, current->comm);
                return -EIO;
        default:
                WARN_ON_ONCE(1);
                return -EIO;
        }
}

/*
 * iomap_dio_rw() always completes O_[D]SYNC writes regardless of whether the IO
 * is being issued as AIO or not.  This allows us to optimise pure data writes
 * to use REQ_FUA rather than requiring generic_write_sync() to issue a
 * REQ_FLUSH post write. This is slightly tricky because a single request here
 * can be mapped into multiple disjoint IOs and only a subset of the IOs issued
 * may be pure data writes. In that case, we still need to do a full data sync
 * completion.
 *
 * When page faults are disabled and @dio_flags includes IOMAP_DIO_PARTIAL,
 * __iomap_dio_rw can return a partial result if it encounters a non-resident
 * page in @iter after preparing a transfer.  In that case, the non-resident
 * pages can be faulted in and the request resumed with @done_before set to the
 * number of bytes previously transferred.  The request will then complete with
 * the correct total number of bytes transferred; this is essential for
 * completing partial requests asynchronously.
 *
 * Returns -ENOTBLK In case of a page invalidation invalidation failure for
 * writes.  The callers needs to fall back to buffered I/O in this case.
 */
struct iomap_dio *
__iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
                const struct iomap_ops *ops, const struct iomap_dio_ops *dops,
                unsigned int dio_flags, void *private, size_t done_before)
{
        struct inode *inode = file_inode(iocb->ki_filp);
        struct iomap_iter iomi = {
                .inode          = inode,
                .pos            = iocb->ki_pos,
                .len            = iov_iter_count(iter),
                .flags          = IOMAP_DIRECT,
                .private        = private,
        };
        bool wait_for_completion =
                is_sync_kiocb(iocb) || (dio_flags & IOMAP_DIO_FORCE_WAIT);
        struct blk_plug plug;
        struct iomap_dio *dio;
        loff_t ret = 0;

        trace_iomap_dio_rw_begin(iocb, iter, dio_flags, done_before);

        if (!iomi.len)
                return NULL;

        dio = kmalloc(sizeof(*dio), GFP_KERNEL);
        if (!dio)
                return ERR_PTR(-ENOMEM);

        dio->iocb = iocb;
        atomic_set(&dio->ref, 1);
        dio->size = 0;
        dio->i_size = i_size_read(inode);
        dio->dops = dops;
        dio->error = 0;
        dio->flags = 0;
        dio->done_before = done_before;

        dio->submit.iter = iter;
        dio->submit.waiter = current;

        if (iocb->ki_flags & IOCB_NOWAIT)
                iomi.flags |= IOMAP_NOWAIT;

        if (iocb->ki_flags & IOCB_ATOMIC)
                iomi.flags |= IOMAP_ATOMIC;

        if (iov_iter_rw(iter) == READ) {
                /* reads can always complete inline */
                dio->flags |= IOMAP_DIO_INLINE_COMP;

                if (iomi.pos >= dio->i_size)
                        goto out_free_dio;

                if (user_backed_iter(iter))
                        dio->flags |= IOMAP_DIO_DIRTY;

                ret = kiocb_write_and_wait(iocb, iomi.len);
                if (ret)
                        goto out_free_dio;
        } else {
                iomi.flags |= IOMAP_WRITE;
                dio->flags |= IOMAP_DIO_WRITE;

                /*
                 * Flag as supporting deferred completions, if the issuer
                 * groks it. This can avoid a workqueue punt for writes.
                 * We may later clear this flag if we need to do other IO
                 * as part of this IO completion.
                 */
                if (iocb->ki_flags & IOCB_DIO_CALLER_COMP)
                        dio->flags |= IOMAP_DIO_CALLER_COMP;

                if (dio_flags & IOMAP_DIO_OVERWRITE_ONLY) {
                        ret = -EAGAIN;
                        if (iomi.pos >= dio->i_size ||
                            iomi.pos + iomi.len > dio->i_size)
                                goto out_free_dio;
                        iomi.flags |= IOMAP_OVERWRITE_ONLY;
                }

                /* for data sync or sync, we need sync completion processing */
                if (iocb_is_dsync(iocb)) {
                        dio->flags |= IOMAP_DIO_NEED_SYNC;

                       /*
                        * For datasync only writes, we optimistically try using
                        * WRITE_THROUGH for this IO. This flag requires either
                        * FUA writes through the device's write cache, or a
                        * normal write to a device without a volatile write
                        * cache. For the former, Any non-FUA write that occurs
                        * will clear this flag, hence we know before completion
                        * whether a cache flush is necessary.
                        */
                        if (!(iocb->ki_flags & IOCB_SYNC))
                                dio->flags |= IOMAP_DIO_WRITE_THROUGH;
                }

                /*
                 * Try to invalidate cache pages for the range we are writing.
                 * If this invalidation fails, let the caller fall back to
                 * buffered I/O.
                 */
                ret = kiocb_invalidate_pages(iocb, iomi.len);
                if (ret) {
                        if (ret != -EAGAIN) {
                                trace_iomap_dio_invalidate_fail(inode, iomi.pos,
                                                                iomi.len);
                                if (iocb->ki_flags & IOCB_ATOMIC) {
                                        /*
                                         * folio invalidation failed, maybe
                                         * this is transient, unlock and see if
                                         * the caller tries again.
                                         */
                                        ret = -EAGAIN;
                                } else {
                                        /* fall back to buffered write */
                                        ret = -ENOTBLK;
                                }
                        }
                        goto out_free_dio;
                }

                if (!wait_for_completion && !inode->i_sb->s_dio_done_wq) {
                        ret = sb_init_dio_done_wq(inode->i_sb);
                        if (ret < 0)
                                goto out_free_dio;
                }
        }

        inode_dio_begin(inode);

        blk_start_plug(&plug);
        while ((ret = iomap_iter(&iomi, ops)) > 0) {
                iomi.processed = iomap_dio_iter(&iomi, dio);

                /*
                 * We can only poll for single bio I/Os.
                 */
                iocb->ki_flags &= ~IOCB_HIPRI;
        }

        blk_finish_plug(&plug);

        /*
         * We only report that we've read data up to i_size.
         * Revert iter to a state corresponding to that as some callers (such
         * as the splice code) rely on it.
         */
        if (iov_iter_rw(iter) == READ && iomi.pos >= dio->i_size)
                iov_iter_revert(iter, iomi.pos - dio->i_size);

        if (ret == -EFAULT && dio->size && (dio_flags & IOMAP_DIO_PARTIAL)) {
                if (!(iocb->ki_flags & IOCB_NOWAIT))
                        wait_for_completion = true;
                ret = 0;
        }

        /* magic error code to fall back to buffered I/O */
        if (ret == -ENOTBLK) {
                wait_for_completion = true;
                ret = 0;
        }
        if (ret < 0)
                iomap_dio_set_error(dio, ret);

        /*
         * If all the writes we issued were already written through to the
         * media, we don't need to flush the cache on IO completion. Clear the
         * sync flag for this case.
         */
        if (dio->flags & IOMAP_DIO_WRITE_THROUGH)
                dio->flags &= ~IOMAP_DIO_NEED_SYNC;

        /*
         * We are about to drop our additional submission reference, which
         * might be the last reference to the dio.  There are three different
         * ways we can progress here:
         *
         *  (a) If this is the last reference we will always complete and free
         *      the dio ourselves.
         *  (b) If this is not the last reference, and we serve an asynchronous
         *      iocb, we must never touch the dio after the decrement, the
         *      I/O completion handler will complete and free it.
         *  (c) If this is not the last reference, but we serve a synchronous
         *      iocb, the I/O completion handler will wake us up on the drop
         *      of the final reference, and we will complete and free it here
         *      after we got woken by the I/O completion handler.
         */
        dio->wait_for_completion = wait_for_completion;
        if (!atomic_dec_and_test(&dio->ref)) {
                if (!wait_for_completion) {
                        trace_iomap_dio_rw_queued(inode, iomi.pos, iomi.len);
                        return ERR_PTR(-EIOCBQUEUED);
                }

                for (;;) {
                        set_current_state(TASK_UNINTERRUPTIBLE);
                        if (!READ_ONCE(dio->submit.waiter))
                                break;

                        blk_io_schedule();
                }
                __set_current_state(TASK_RUNNING);
        }

        return dio;

out_free_dio:
        kfree(dio);
        if (ret)
                return ERR_PTR(ret);
        return NULL;
}
EXPORT_SYMBOL_GPL(__iomap_dio_rw);

ssize_t
iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
                const struct iomap_ops *ops, const struct iomap_dio_ops *dops,
                unsigned int dio_flags, void *private, size_t done_before)
{
        struct iomap_dio *dio;

        dio = __iomap_dio_rw(iocb, iter, ops, dops, dio_flags, private,
                             done_before);
        if (IS_ERR_OR_NULL(dio))
                return PTR_ERR_OR_ZERO(dio);
        return iomap_dio_complete(dio);
}
EXPORT_SYMBOL_GPL(iomap_dio_rw);

static int __init iomap_dio_init(void)
{
        zero_page = alloc_pages(GFP_KERNEL | __GFP_ZERO,
                                IOMAP_ZERO_PAGE_ORDER);

        if (!zero_page)
                return -ENOMEM;

        return 0;
}
fs_initcall(iomap_dio_init);