linux/fs/btrfs/direct-io.c

// SPDX-License-Identifier: GPL-2.0

#include <linux/fsverity.h>
#include <linux/iomap.h>
#include "ctree.h"
#include "delalloc-space.h"
#include "direct-io.h"
#include "extent-tree.h"
#include "file.h"
#include "fs.h"
#include "transaction.h"
#include "volumes.h"

struct btrfs_dio_data {
	ssize_t submitted;
	struct extent_changeset *data_reserved;
	struct btrfs_ordered_extent *ordered;
	bool data_space_reserved;
	bool nocow_done;
};

struct btrfs_dio_private {
	/* Range of I/O */
	u64 file_offset;
	u32 bytes;

	/* This must be last */
	struct btrfs_bio bbio;
};

static struct bio_set btrfs_dio_bioset;

static int lock_extent_direct(struct inode *inode, u64 lockstart, u64 lockend,
			      struct extent_state **cached_state,
			      unsigned int iomap_flags)
{
	const bool writing = (iomap_flags & IOMAP_WRITE);
	const bool nowait = (iomap_flags & IOMAP_NOWAIT);
	struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
	struct btrfs_ordered_extent *ordered;
	int ret = 0;

	while (1) {
		if (nowait) {
			if (!try_lock_extent(io_tree, lockstart, lockend,
					     cached_state))
				return -EAGAIN;
		} else {
			lock_extent(io_tree, lockstart, lockend, cached_state);
		}
		/*
		 * We're concerned with the entire range that we're going to be
		 * doing DIO to, so we need to make sure there's no ordered
		 * extents in this range.
		 */
		ordered = btrfs_lookup_ordered_range(BTRFS_I(inode), lockstart,
						     lockend - lockstart + 1);

		/*
		 * We need to make sure there are no buffered pages in this
		 * range either, we could have raced between the invalidate in
		 * generic_file_direct_write and locking the extent.  The
		 * invalidate needs to happen so that reads after a write do not
		 * get stale data.
		 */
		if (!ordered &&
		    (!writing || !filemap_range_has_page(inode->i_mapping,
							 lockstart, lockend)))
			break;

		unlock_extent(io_tree, lockstart, lockend, cached_state);

		if (ordered) {
			if (nowait) {
				btrfs_put_ordered_extent(ordered);
				ret = -EAGAIN;
				break;
			}
			/*
			 * If we are doing a DIO read and the ordered extent we
			 * found is for a buffered write, we can not wait for it
			 * to complete and retry, because if we do so we can
			 * deadlock with concurrent buffered writes on page
			 * locks. This happens only if our DIO read covers more
			 * than one extent map, if at this point has already
			 * created an ordered extent for a previous extent map
			 * and locked its range in the inode's io tree, and a
			 * concurrent write against that previous extent map's
			 * range and this range started (we unlock the ranges
			 * in the io tree only when the bios complete and
			 * buffered writes always lock pages before attempting
			 * to lock range in the io tree).
			 */
			if (writing ||
			    test_bit(BTRFS_ORDERED_DIRECT, &ordered->flags))
				btrfs_start_ordered_extent(ordered);
			else
				ret = nowait ? -EAGAIN : -ENOTBLK;
			btrfs_put_ordered_extent(ordered);
		} else {
			/*
			 * We could trigger writeback for this range (and wait
			 * for it to complete) and then invalidate the pages for
			 * this range (through invalidate_inode_pages2_range()),
			 * but that can lead us to a deadlock with a concurrent
			 * call to readahead (a buffered read or a defrag call
			 * triggered a readahead) on a page lock due to an
			 * ordered dio extent we created before but did not have
			 * yet a corresponding bio submitted (whence it can not
			 * complete), which makes readahead wait for that
			 * ordered extent to complete while holding a lock on
			 * that page.
			 */
			ret = nowait ? -EAGAIN : -ENOTBLK;
		}

		if (ret)
			break;

		cond_resched();
	}

	return ret;
}

static struct extent_map *btrfs_create_dio_extent(struct btrfs_inode *inode,
						  struct btrfs_dio_data *dio_data,
						  const u64 start,
						  const struct btrfs_file_extent *file_extent,
						  const int type)
{
	struct extent_map *em = NULL;
	struct btrfs_ordered_extent *ordered;

	if (type != BTRFS_ORDERED_NOCOW) {
		em = btrfs_create_io_em(inode, start, file_extent, type);
		if (IS_ERR(em))
			goto out;
	}

	ordered = btrfs_alloc_ordered_extent(inode, start, file_extent,
					     (1 << type) |
					     (1 << BTRFS_ORDERED_DIRECT));
	if (IS_ERR(ordered)) {
		if (em) {
			free_extent_map(em);
			btrfs_drop_extent_map_range(inode, start,
					start + file_extent->num_bytes - 1, false);
		}
		em = ERR_CAST(ordered);
	} else {
		ASSERT(!dio_data->ordered);
		dio_data->ordered = ordered;
	}
 out:

	return em;
}

static struct extent_map *btrfs_new_extent_direct(struct btrfs_inode *inode,
						  struct btrfs_dio_data *dio_data,
						  u64 start, u64 len)
{
	struct btrfs_root *root = inode->root;
	struct btrfs_fs_info *fs_info = root->fs_info;
	struct btrfs_file_extent file_extent;
	struct extent_map *em;
	struct btrfs_key ins;
	u64 alloc_hint;
	int ret;

	alloc_hint = btrfs_get_extent_allocation_hint(inode, start, len);
again:
	ret = btrfs_reserve_extent(root, len, len, fs_info->sectorsize,
				   0, alloc_hint, &ins, 1, 1);
	if (ret == -EAGAIN) {
		ASSERT(btrfs_is_zoned(fs_info));
		wait_on_bit_io(&inode->root->fs_info->flags, BTRFS_FS_NEED_ZONE_FINISH,
			       TASK_UNINTERRUPTIBLE);
		goto again;
	}
	if (ret)
		return ERR_PTR(ret);

	file_extent.disk_bytenr = ins.objectid;
	file_extent.disk_num_bytes = ins.offset;
	file_extent.num_bytes = ins.offset;
	file_extent.ram_bytes = ins.offset;
	file_extent.offset = 0;
	file_extent.compression = BTRFS_COMPRESS_NONE;
	em = btrfs_create_dio_extent(inode, dio_data, start, &file_extent,
				     BTRFS_ORDERED_REGULAR);
	btrfs_dec_block_group_reservations(fs_info, ins.objectid);
	if (IS_ERR(em))
		btrfs_free_reserved_extent(fs_info, ins.objectid, ins.offset,
					   1);

	return em;
}

static int btrfs_get_blocks_direct_write(struct extent_map **map,
					 struct inode *inode,
					 struct btrfs_dio_data *dio_data,
					 u64 start, u64 *lenp,
					 unsigned int iomap_flags)
{
	const bool nowait = (iomap_flags & IOMAP_NOWAIT);
	struct btrfs_fs_info *fs_info = inode_to_fs_info(inode);
	struct btrfs_file_extent file_extent;
	struct extent_map *em = *map;
	int type;
	u64 block_start;
	struct btrfs_block_group *bg;
	bool can_nocow = false;
	bool space_reserved = false;
	u64 len = *lenp;
	u64 prev_len;
	int ret = 0;

	/*
	 * We don't allocate a new extent in the following cases
	 *
	 * 1) The inode is marked as NODATACOW. In this case we'll just use the
	 * existing extent.
	 * 2) The extent is marked as PREALLOC. We're good to go here and can
	 * just use the extent.
	 *
	 */
	if ((em->flags & EXTENT_FLAG_PREALLOC) ||
	    ((BTRFS_I(inode)->flags & BTRFS_INODE_NODATACOW) &&
	     em->disk_bytenr != EXTENT_MAP_HOLE)) {
		if (em->flags & EXTENT_FLAG_PREALLOC)
			type = BTRFS_ORDERED_PREALLOC;
		else
			type = BTRFS_ORDERED_NOCOW;
		len = min(len, em->len - (start - em->start));
		block_start = extent_map_block_start(em) + (start - em->start);

		if (can_nocow_extent(inode, start, &len,
				     &file_extent, false, false) == 1) {
			bg = btrfs_inc_nocow_writers(fs_info, block_start);
			if (bg)
				can_nocow = true;
		}
	}

	prev_len = len;
	if (can_nocow) {
		struct extent_map *em2;

		/* We can NOCOW, so only need to reserve metadata space. */
		ret = btrfs_delalloc_reserve_metadata(BTRFS_I(inode), len, len,
						      nowait);
		if (ret < 0) {
			/* Our caller expects us to free the input extent map. */
			free_extent_map(em);
			*map = NULL;
			btrfs_dec_nocow_writers(bg);
			if (nowait && (ret == -ENOSPC || ret == -EDQUOT))
				ret = -EAGAIN;
			goto out;
		}
		space_reserved = true;

		em2 = btrfs_create_dio_extent(BTRFS_I(inode), dio_data, start,
					      &file_extent, type);
		btrfs_dec_nocow_writers(bg);
		if (type == BTRFS_ORDERED_PREALLOC) {
			free_extent_map(em);
			*map = em2;
			em = em2;
		}

		if (IS_ERR(em2)) {
			ret = PTR_ERR(em2);
			goto out;
		}

		dio_data->nocow_done = true;
	} else {
		/* Our caller expects us to free the input extent map. */
		free_extent_map(em);
		*map = NULL;

		if (nowait) {
			ret = -EAGAIN;
			goto out;
		}

		/*
		 * If we could not allocate data space before locking the file
		 * range and we can't do a NOCOW write, then we have to fail.
		 */
		if (!dio_data->data_space_reserved) {
			ret = -ENOSPC;
			goto out;
		}

		/*
		 * We have to COW and we have already reserved data space before,
		 * so now we reserve only metadata.
		 */
		ret = btrfs_delalloc_reserve_metadata(BTRFS_I(inode), len, len,
						      false);
		if (ret < 0)
			goto out;
		space_reserved = true;

		em = btrfs_new_extent_direct(BTRFS_I(inode), dio_data, start, len);
		if (IS_ERR(em)) {
			ret = PTR_ERR(em);
			goto out;
		}
		*map = em;
		len = min(len, em->len - (start - em->start));
		if (len < prev_len)
			btrfs_delalloc_release_metadata(BTRFS_I(inode),
							prev_len - len, true);
	}

	/*
	 * We have created our ordered extent, so we can now release our reservation
	 * for an outstanding extent.
	 */
	btrfs_delalloc_release_extents(BTRFS_I(inode), prev_len);

	/*
	 * Need to update the i_size under the extent lock so buffered
	 * readers will get the updated i_size when we unlock.
	 */
	if (start + len > i_size_read(inode))
		i_size_write(inode, start + len);
out:
	if (ret && space_reserved) {
		btrfs_delalloc_release_extents(BTRFS_I(inode), len);
		btrfs_delalloc_release_metadata(BTRFS_I(inode), len, true);
	}
	*lenp = len;
	return ret;
}

static int btrfs_dio_iomap_begin(struct inode *inode, loff_t start,
		loff_t length, unsigned int flags, struct iomap *iomap,
		struct iomap *srcmap)
{
	struct iomap_iter *iter = container_of(iomap, struct iomap_iter, iomap);
	struct btrfs_fs_info *fs_info = inode_to_fs_info(inode);
	struct extent_map *em;
	struct extent_state *cached_state = NULL;
	struct btrfs_dio_data *dio_data = iter->private;
	u64 lockstart, lockend;
	const bool write = !!(flags & IOMAP_WRITE);
	int ret = 0;
	u64 len = length;
	const u64 data_alloc_len = length;
	bool unlock_extents = false;

	/*
	 * We could potentially fault if we have a buffer > PAGE_SIZE, and if
	 * we're NOWAIT we may submit a bio for a partial range and return
	 * EIOCBQUEUED, which would result in an errant short read.
	 *
	 * The best way to handle this would be to allow for partial completions
	 * of iocb's, so we could submit the partial bio, return and fault in
	 * the rest of the pages, and then submit the io for the rest of the
	 * range.  However we don't have that currently, so simply return
	 * -EAGAIN at this point so that the normal path is used.
	 */
	if (!write && (flags & IOMAP_NOWAIT) && length > PAGE_SIZE)
		return -EAGAIN;

	/*
	 * Cap the size of reads to that usually seen in buffered I/O as we need
	 * to allocate a contiguous array for the checksums.
	 */
	if (!write)
		len = min_t(u64, len, fs_info->sectorsize * BTRFS_MAX_BIO_SECTORS);

	lockstart = start;
	lockend = start + len - 1;

	/*
	 * iomap_dio_rw() only does filemap_write_and_wait_range(), which isn't
	 * enough if we've written compressed pages to this area, so we need to
	 * flush the dirty pages again to make absolutely sure that any
	 * outstanding dirty pages are on disk - the first flush only starts
	 * compression on the data, while keeping the pages locked, so by the
	 * time the second flush returns we know bios for the compressed pages
	 * were submitted and finished, and the pages no longer under writeback.
	 *
	 * If we have a NOWAIT request and we have any pages in the range that
	 * are locked, likely due to compression still in progress, we don't want
	 * to block on page locks. We also don't want to block on pages marked as
	 * dirty or under writeback (same as for the non-compression case).
	 * iomap_dio_rw() did the same check, but after that and before we got
	 * here, mmap'ed writes may have happened or buffered reads started
	 * (readpage() and readahead(), which lock pages), as we haven't locked
	 * the file range yet.
	 */
	if (test_bit(BTRFS_INODE_HAS_ASYNC_EXTENT,
		     &BTRFS_I(inode)->runtime_flags)) {
		if (flags & IOMAP_NOWAIT) {
			if (filemap_range_needs_writeback(inode->i_mapping,
							  lockstart, lockend))
				return -EAGAIN;
		} else {
			ret = filemap_fdatawrite_range(inode->i_mapping, start,
						       start + length - 1);
			if (ret)
				return ret;
		}
	}

	memset(dio_data, 0, sizeof(*dio_data));

	/*
	 * We always try to allocate data space and must do it before locking
	 * the file range, to avoid deadlocks with concurrent writes to the same
	 * range if the range has several extents and the writes don't expand the
	 * current i_size (the inode lock is taken in shared mode). If we fail to
	 * allocate data space here we continue and later, after locking the
	 * file range, we fail with ENOSPC only if we figure out we can not do a
	 * NOCOW write.
	 */
	if (write && !(flags & IOMAP_NOWAIT)) {
		ret = btrfs_check_data_free_space(BTRFS_I(inode),
						  &dio_data->data_reserved,
						  start, data_alloc_len, false);
		if (!ret)
			dio_data->data_space_reserved = true;
		else if (ret && !(BTRFS_I(inode)->flags &
				  (BTRFS_INODE_NODATACOW | BTRFS_INODE_PREALLOC)))
			goto err;
	}

	/*
	 * If this errors out it's because we couldn't invalidate pagecache for
	 * this range and we need to fallback to buffered IO, or we are doing a
	 * NOWAIT read/write and we need to block.
	 */
	ret = lock_extent_direct(inode, lockstart, lockend, &cached_state, flags);
	if (ret < 0)
		goto err;

	em = btrfs_get_extent(BTRFS_I(inode), NULL, start, len);
	if (IS_ERR(em)) {
		ret = PTR_ERR(em);
		goto unlock_err;
	}

	/*
	 * Ok for INLINE and COMPRESSED extents we need to fallback on buffered
	 * io.  INLINE is special, and we could probably kludge it in here, but
	 * it's still buffered so for safety lets just fall back to the generic
	 * buffered path.
	 *
	 * For COMPRESSED we _have_ to read the entire extent in so we can
	 * decompress it, so there will be buffering required no matter what we
	 * do, so go ahead and fallback to buffered.
	 *
	 * We return -ENOTBLK because that's what makes DIO go ahead and go back
	 * to buffered IO.  Don't blame me, this is the price we pay for using
	 * the generic code.
	 */
	if (extent_map_is_compressed(em) || em->disk_bytenr == EXTENT_MAP_INLINE) {
		free_extent_map(em);
		/*
		 * If we are in a NOWAIT context, return -EAGAIN in order to
		 * fallback to buffered IO. This is not only because we can
		 * block with buffered IO (no support for NOWAIT semantics at
		 * the moment) but also to avoid returning short reads to user
		 * space - this happens if we were able to read some data from
		 * previous non-compressed extents and then when we fallback to
		 * buffered IO, at btrfs_file_read_iter() by calling
		 * filemap_read(), we fail to fault in pages for the read buffer,
		 * in which case filemap_read() returns a short read (the number
		 * of bytes previously read is > 0, so it does not return -EFAULT).
		 */
		ret = (flags & IOMAP_NOWAIT) ? -EAGAIN : -ENOTBLK;
		goto unlock_err;
	}

	len = min(len, em->len - (start - em->start));

	/*
	 * If we have a NOWAIT request and the range contains multiple extents
	 * (or a mix of extents and holes), then we return -EAGAIN to make the
	 * caller fallback to a context where it can do a blocking (without
	 * NOWAIT) request. This way we avoid doing partial IO and returning
	 * success to the caller, which is not optimal for writes and for reads
	 * it can result in unexpected behaviour for an application.
	 *
	 * When doing a read, because we use IOMAP_DIO_PARTIAL when calling
	 * iomap_dio_rw(), we can end up returning less data then what the caller
	 * asked for, resulting in an unexpected, and incorrect, short read.
	 * That is, the caller asked to read N bytes and we return less than that,
	 * which is wrong unless we are crossing EOF. This happens if we get a
	 * page fault error when trying to fault in pages for the buffer that is
	 * associated to the struct iov_iter passed to iomap_dio_rw(), and we
	 * have previously submitted bios for other extents in the range, in
	 * which case iomap_dio_rw() may return us EIOCBQUEUED if not all of
	 * those bios have completed by the time we get the page fault error,
	 * which we return back to our caller - we should only return EIOCBQUEUED
	 * after we have submitted bios for all the extents in the range.
	 */
	if ((flags & IOMAP_NOWAIT) && len < length) {
		free_extent_map(em);
		ret = -EAGAIN;
		goto unlock_err;
	}

	if (write) {
		ret = btrfs_get_blocks_direct_write(&em, inode, dio_data,
						    start, &len, flags);
		if (ret < 0)
			goto unlock_err;
		unlock_extents = true;
		/* Recalc len in case the new em is smaller than requested */
		len = min(len, em->len - (start - em->start));
		if (dio_data->data_space_reserved) {
			u64 release_offset;
			u64 release_len = 0;

			if (dio_data->nocow_done) {
				release_offset = start;
				release_len = data_alloc_len;
			} else if (len < data_alloc_len) {
				release_offset = start + len;
				release_len = data_alloc_len - len;
			}

			if (release_len > 0)
				btrfs_free_reserved_data_space(BTRFS_I(inode),
							       dio_data->data_reserved,
							       release_offset,
							       release_len);
		}
	} else {
		/*
		 * We need to unlock only the end area that we aren't using.
		 * The rest is going to be unlocked by the endio routine.
		 */
		lockstart = start + len;
		if (lockstart < lockend)
			unlock_extents = true;
	}

	if (unlock_extents)
		unlock_extent(&BTRFS_I(inode)->io_tree, lockstart, lockend,
			      &cached_state);
	else
		free_extent_state(cached_state);

	/*
	 * Translate extent map information to iomap.
	 * We trim the extents (and move the addr) even though iomap code does
	 * that, since we have locked only the parts we are performing I/O in.
	 */
	if ((em->disk_bytenr == EXTENT_MAP_HOLE) ||
	    ((em->flags & EXTENT_FLAG_PREALLOC) && !write)) {
		iomap->addr = IOMAP_NULL_ADDR;
		iomap->type = IOMAP_HOLE;
	} else {
		iomap->addr = extent_map_block_start(em) + (start - em->start);
		iomap->type = IOMAP_MAPPED;
	}
	iomap->offset = start;
	iomap->bdev = fs_info->fs_devices->latest_dev->bdev;
	iomap->length = len;
	free_extent_map(em);

	return 0;

unlock_err:
	unlock_extent(&BTRFS_I(inode)->io_tree, lockstart, lockend,
		      &cached_state);
err:
	if (dio_data->data_space_reserved) {
		btrfs_free_reserved_data_space(BTRFS_I(inode),
					       dio_data->data_reserved,
					       start, data_alloc_len);
		extent_changeset_free(dio_data->data_reserved);
	}

	return ret;
}

static int btrfs_dio_iomap_end(struct inode *inode, loff_t pos, loff_t length,
		ssize_t written, unsigned int flags, struct iomap *iomap)
{
	struct iomap_iter *iter = container_of(iomap, struct iomap_iter, iomap);
	struct btrfs_dio_data *dio_data = iter->private;
	size_t submitted = dio_data->submitted;
	const bool write = !!(flags & IOMAP_WRITE);
	int ret = 0;

	if (!write && (iomap->type == IOMAP_HOLE)) {
		/* If reading from a hole, unlock and return */
		unlock_extent(&BTRFS_I(inode)->io_tree, pos, pos + length - 1,
			      NULL);
		return 0;
	}

	if (submitted < length) {
		pos += submitted;
		length -= submitted;
		if (write)
			btrfs_finish_ordered_extent(dio_data->ordered, NULL,
						    pos, length, false);
		else
			unlock_extent(&BTRFS_I(inode)->io_tree, pos,
				      pos + length - 1, NULL);
		ret = -ENOTBLK;
	}
	if (write) {
		btrfs_put_ordered_extent(dio_data->ordered);
		dio_data->ordered = NULL;
	}

	if (write)
		extent_changeset_free(dio_data->data_reserved);
	return ret;
}

static void btrfs_dio_end_io(struct btrfs_bio *bbio)
{
	struct btrfs_dio_private *dip =
		container_of(bbio, struct btrfs_dio_private, bbio);
	struct btrfs_inode *inode = bbio->inode;
	struct bio *bio = &bbio->bio;

	if (bio->bi_status) {
		btrfs_warn(inode->root->fs_info,
		"direct IO failed ino %llu op 0x%0x offset %#llx len %u err no %d",
			   btrfs_ino(inode), bio->bi_opf,
			   dip->file_offset, dip->bytes, bio->bi_status);
	}

	if (btrfs_op(bio) == BTRFS_MAP_WRITE) {
		btrfs_finish_ordered_extent(bbio->ordered, NULL,
					    dip->file_offset, dip->bytes,
					    !bio->bi_status);
	} else {
		unlock_extent(&inode->io_tree, dip->file_offset,
			      dip->file_offset + dip->bytes - 1, NULL);
	}

	bbio->bio.bi_private = bbio->private;
	iomap_dio_bio_end_io(bio);
}

static int btrfs_extract_ordered_extent(struct btrfs_bio *bbio,
					struct btrfs_ordered_extent *ordered)
{
	u64 start = (u64)bbio->bio.bi_iter.bi_sector << SECTOR_SHIFT;
	u64 len = bbio->bio.bi_iter.bi_size;
	struct btrfs_ordered_extent *new;
	int ret;

	/* Must always be called for the beginning of an ordered extent. */
	if (WARN_ON_ONCE(start != ordered->disk_bytenr))
		return -EINVAL;

	/* No need to split if the ordered extent covers the entire bio. */
	if (ordered->disk_num_bytes == len) {
		refcount_inc(&ordered->refs);
		bbio->ordered = ordered;
		return 0;
	}

	/*
	 * Don't split the extent_map for NOCOW extents, as we're writing into
	 * a pre-existing one.
	 */
	if (!test_bit(BTRFS_ORDERED_NOCOW, &ordered->flags)) {
		ret = split_extent_map(bbio->inode, bbio->file_offset,
				       ordered->num_bytes, len,
				       ordered->disk_bytenr);
		if (ret)
			return ret;
	}

	new = btrfs_split_ordered_extent(ordered, len);
	if (IS_ERR(new))
		return PTR_ERR(new);
	bbio->ordered = new;
	return 0;
}

static void btrfs_dio_submit_io(const struct iomap_iter *iter, struct bio *bio,
				loff_t file_offset)
{
	struct btrfs_bio *bbio = btrfs_bio(bio);
	struct btrfs_dio_private *dip =
		container_of(bbio, struct btrfs_dio_private, bbio);
	struct btrfs_dio_data *dio_data = iter->private;

	btrfs_bio_init(bbio, BTRFS_I(iter->inode)->root->fs_info,
		       btrfs_dio_end_io, bio->bi_private);
	bbio->inode = BTRFS_I(iter->inode);
	bbio->file_offset = file_offset;

	dip->file_offset = file_offset;
	dip->bytes = bio->bi_iter.bi_size;

	dio_data->submitted += bio->bi_iter.bi_size;

	/*
	 * Check if we are doing a partial write.  If we are, we need to split
	 * the ordered extent to match the submitted bio.  Hang on to the
	 * remaining unfinishable ordered_extent in dio_data so that it can be
	 * cancelled in iomap_end to avoid a deadlock wherein faulting the
	 * remaining pages is blocked on the outstanding ordered extent.
	 */
	if (iter->flags & IOMAP_WRITE) {
		int ret;

		ret = btrfs_extract_ordered_extent(bbio, dio_data->ordered);
		if (ret) {
			btrfs_finish_ordered_extent(dio_data->ordered, NULL,
						    file_offset, dip->bytes,
						    !ret);
			bio->bi_status = errno_to_blk_status(ret);
			iomap_dio_bio_end_io(bio);
			return;
		}
	}

	btrfs_submit_bbio(bbio, 0);
}

static const struct iomap_ops btrfs_dio_iomap_ops = {
	.iomap_begin            = btrfs_dio_iomap_begin,
	.iomap_end              = btrfs_dio_iomap_end,
};

static const struct iomap_dio_ops btrfs_dio_ops = {
	.submit_io		= btrfs_dio_submit_io,
	.bio_set		= &btrfs_dio_bioset,
};

static ssize_t btrfs_dio_read(struct kiocb *iocb, struct iov_iter *iter,
			      size_t done_before)
{
	struct btrfs_dio_data data = { 0 };

	return iomap_dio_rw(iocb, iter, &btrfs_dio_iomap_ops, &btrfs_dio_ops,
			    IOMAP_DIO_PARTIAL, &data, done_before);
}

static struct iomap_dio *btrfs_dio_write(struct kiocb *iocb, struct iov_iter *iter,
					 size_t done_before)
{
	struct btrfs_dio_data data = { 0 };

	return __iomap_dio_rw(iocb, iter, &btrfs_dio_iomap_ops, &btrfs_dio_ops,
			    IOMAP_DIO_PARTIAL, &data, done_before);
}

static ssize_t check_direct_IO(struct btrfs_fs_info *fs_info,
			       const struct iov_iter *iter, loff_t offset)
{
	const u32 blocksize_mask = fs_info->sectorsize - 1;

	if (offset & blocksize_mask)
		return -EINVAL;

	if (iov_iter_alignment(iter) & blocksize_mask)
		return -EINVAL;

	return 0;
}

ssize_t btrfs_direct_write(struct kiocb *iocb, struct iov_iter *from)
{
	struct file *file = iocb->ki_filp;
	struct inode *inode = file_inode(file);
	struct btrfs_fs_info *fs_info = inode_to_fs_info(inode);
	loff_t pos;
	ssize_t written = 0;
	ssize_t written_buffered;
	size_t prev_left = 0;
	loff_t endbyte;
	ssize_t ret;
	unsigned int ilock_flags = 0;
	struct iomap_dio *dio;

	if (iocb->ki_flags & IOCB_NOWAIT)
		ilock_flags |= BTRFS_ILOCK_TRY;

	/*
	 * If the write DIO is within EOF, use a shared lock and also only if
	 * security bits will likely not be dropped by file_remove_privs() called
	 * from btrfs_write_check(). Either will need to be rechecked after the
	 * lock was acquired.
	 */
	if (iocb->ki_pos + iov_iter_count(from) <= i_size_read(inode) && IS_NOSEC(inode))
		ilock_flags |= BTRFS_ILOCK_SHARED;

relock:
	ret = btrfs_inode_lock(BTRFS_I(inode), ilock_flags);
	if (ret < 0)
		return ret;

	/* Shared lock cannot be used with security bits set. */
	if ((ilock_flags & BTRFS_ILOCK_SHARED) && !IS_NOSEC(inode)) {
		btrfs_inode_unlock(BTRFS_I(inode), ilock_flags);
		ilock_flags &= ~BTRFS_ILOCK_SHARED;
		goto relock;
	}

	ret = generic_write_checks(iocb, from);
	if (ret <= 0) {
		btrfs_inode_unlock(BTRFS_I(inode), ilock_flags);
		return ret;
	}

	ret = btrfs_write_check(iocb, from, ret);
	if (ret < 0) {
		btrfs_inode_unlock(BTRFS_I(inode), ilock_flags);
		goto out;
	}

	pos = iocb->ki_pos;
	/*
	 * Re-check since file size may have changed just before taking the
	 * lock or pos may have changed because of O_APPEND in generic_write_check()
	 */
	if ((ilock_flags & BTRFS_ILOCK_SHARED) &&
	    pos + iov_iter_count(from) > i_size_read(inode)) {
		btrfs_inode_unlock(BTRFS_I(inode), ilock_flags);
		ilock_flags &= ~BTRFS_ILOCK_SHARED;
		goto relock;
	}

	if (check_direct_IO(fs_info, from, pos)) {
		btrfs_inode_unlock(BTRFS_I(inode), ilock_flags);
		goto buffered;
	}

	/*
	 * The iov_iter can be mapped to the same file range we are writing to.
	 * If that's the case, then we will deadlock in the iomap code, because
	 * it first calls our callback btrfs_dio_iomap_begin(), which will create
	 * an ordered extent, and after that it will fault in the pages that the
	 * iov_iter refers to. During the fault in we end up in the readahead
	 * pages code (starting at btrfs_readahead()), which will lock the range,
	 * find that ordered extent and then wait for it to complete (at
	 * btrfs_lock_and_flush_ordered_range()), resulting in a deadlock since
	 * obviously the ordered extent can never complete as we didn't submit
	 * yet the respective bio(s). This always happens when the buffer is
	 * memory mapped to the same file range, since the iomap DIO code always
	 * invalidates pages in the target file range (after starting and waiting
	 * for any writeback).
	 *
	 * So here we disable page faults in the iov_iter and then retry if we
	 * got -EFAULT, faulting in the pages before the retry.
	 */
again:
	from->nofault = true;
	dio = btrfs_dio_write(iocb, from, written);
	from->nofault = false;

	if (IS_ERR_OR_NULL(dio)) {
		ret = PTR_ERR_OR_ZERO(dio);
	} else {
		/*
		 * If we have a synchronous write, we must make sure the fsync
		 * triggered by the iomap_dio_complete() call below doesn't
		 * deadlock on the inode lock - we are already holding it and we
		 * can't call it after unlocking because we may need to complete
		 * partial writes due to the input buffer (or parts of it) not
		 * being already faulted in.
		 */
		ASSERT(current->journal_info == NULL);
		current->journal_info = BTRFS_TRANS_DIO_WRITE_STUB;
		ret = iomap_dio_complete(dio);
		current->journal_info = NULL;
	}

	/* No increment (+=) because iomap returns a cumulative value. */
	if (ret > 0)
		written = ret;

	if (iov_iter_count(from) > 0 && (ret == -EFAULT || ret > 0)) {
		const size_t left = iov_iter_count(from);
		/*
		 * We have more data left to write. Try to fault in as many as
		 * possible of the remainder pages and retry. We do this without
		 * releasing and locking again the inode, to prevent races with
		 * truncate.
		 *
		 * Also, in case the iov refers to pages in the file range of the
		 * file we want to write to (due to a mmap), we could enter an
		 * infinite loop if we retry after faulting the pages in, since
		 * iomap will invalidate any pages in the range early on, before
		 * it tries to fault in the pages of the iov. So we keep track of
		 * how much was left of iov in the previous EFAULT and fallback
		 * to buffered IO in case we haven't made any progress.
		 */
		if (left == prev_left) {
			ret = -ENOTBLK;
		} else {
			fault_in_iov_iter_readable(from, left);
			prev_left = left;
			goto again;
		}
	}

	btrfs_inode_unlock(BTRFS_I(inode), ilock_flags);

	/*
	 * If 'ret' is -ENOTBLK or we have not written all data, then it means
	 * we must fallback to buffered IO.
	 */
	if ((ret < 0 && ret != -ENOTBLK) || !iov_iter_count(from))
		goto out;

buffered:
	/*
	 * If we are in a NOWAIT context, then return -EAGAIN to signal the caller
	 * it must retry the operation in a context where blocking is acceptable,
	 * because even if we end up not blocking during the buffered IO attempt
	 * below, we will block when flushing and waiting for the IO.
	 */
	if (iocb->ki_flags & IOCB_NOWAIT) {
		ret = -EAGAIN;
		goto out;
	}

	pos = iocb->ki_pos;
	written_buffered = btrfs_buffered_write(iocb, from);
	if (written_buffered < 0) {
		ret = written_buffered;
		goto out;
	}
	/*
	 * Ensure all data is persisted. We want the next direct IO read to be
	 * able to read what was just written.
	 */
	endbyte = pos + written_buffered - 1;
	ret = btrfs_fdatawrite_range(BTRFS_I(inode), pos, endbyte);
	if (ret)
		goto out;
	ret = filemap_fdatawait_range(inode->i_mapping, pos, endbyte);
	if (ret)
		goto out;
	written += written_buffered;
	iocb->ki_pos = pos + written_buffered;
	invalidate_mapping_pages(file->f_mapping, pos >> PAGE_SHIFT,
				 endbyte >> PAGE_SHIFT);
out:
	return ret < 0 ? ret : written;
}

static int check_direct_read(struct btrfs_fs_info *fs_info,
			     const struct iov_iter *iter, loff_t offset)
{
	int ret;
	int i, seg;

	ret = check_direct_IO(fs_info, iter, offset);
	if (ret < 0)
		return ret;

	if (!iter_is_iovec(iter))
		return 0;

	for (seg = 0; seg < iter->nr_segs; seg++) {
		for (i = seg + 1; i < iter->nr_segs; i++) {
			const struct iovec *iov1 = iter_iov(iter) + seg;
			const struct iovec *iov2 = iter_iov(iter) + i;

			if (iov1->iov_base == iov2->iov_base)
				return -EINVAL;
		}
	}
	return 0;
}

ssize_t btrfs_direct_read(struct kiocb *iocb, struct iov_iter *to)
{
	struct inode *inode = file_inode(iocb->ki_filp);
	size_t prev_left = 0;
	ssize_t read = 0;
	ssize_t ret;

	if (fsverity_active(inode))
		return 0;

	if (check_direct_read(inode_to_fs_info(inode), to, iocb->ki_pos))
		return 0;

	btrfs_inode_lock(BTRFS_I(inode), BTRFS_ILOCK_SHARED);
again:
	/*
	 * This is similar to what we do for direct IO writes, see the comment
	 * at btrfs_direct_write(), but we also disable page faults in addition
	 * to disabling them only at the iov_iter level. This is because when
	 * reading from a hole or prealloc extent, iomap calls iov_iter_zero(),
	 * which can still trigger page fault ins despite having set ->nofault
	 * to true of our 'to' iov_iter.
	 *
	 * The difference to direct IO writes is that we deadlock when trying
	 * to lock the extent range in the inode's tree during he page reads
	 * triggered by the fault in (while for writes it is due to waiting for
	 * our own ordered extent). This is because for direct IO reads,
	 * btrfs_dio_iomap_begin() returns with the extent range locked, which
	 * is only unlocked in the endio callback (end_bio_extent_readpage()).
	 */
	pagefault_disable();
	to->nofault = true;
	ret = btrfs_dio_read(iocb, to, read);
	to->nofault = false;
	pagefault_enable();

	/* No increment (+=) because iomap returns a cumulative value. */
	if (ret > 0)
		read = ret;

	if (iov_iter_count(to) > 0 && (ret == -EFAULT || ret > 0)) {
		const size_t left = iov_iter_count(to);

		if (left == prev_left) {
			/*
			 * We didn't make any progress since the last attempt,
			 * fallback to a buffered read for the remainder of the
			 * range. This is just to avoid any possibility of looping
			 * for too long.
			 */
			ret = read;
		} else {
			/*
			 * We made some progress since the last retry or this is
			 * the first time we are retrying. Fault in as many pages
			 * as possible and retry.
			 */
			fault_in_iov_iter_writeable(to, left);
			prev_left = left;
			goto again;
		}
	}
	btrfs_inode_unlock(BTRFS_I(inode), BTRFS_ILOCK_SHARED);
	return ret < 0 ? ret : read;
}

int __init btrfs_init_dio(void)
{
	if (bioset_init(&btrfs_dio_bioset, BIO_POOL_SIZE,
			offsetof(struct btrfs_dio_private, bbio.bio),
			BIOSET_NEED_BVECS))
		return -ENOMEM;

	return 0;
}

void __cold btrfs_destroy_dio(void)
{
	bioset_exit(&btrfs_dio_bioset);
}