From: Filipe Manana fdmanana@suse.com

Commit f0bfa76a11e93d0fe2c896fcb566568c5e8b5d3f upstream.

When doing a direct IO write against a file range that either has preallocated extents in that range or has regular extents and the file has the NOCOW attribute set, the write fails with -ENOSPC when all of the following conditions are met:

1) There are no data blocks groups with enough free space matching the size of the write;

2) There's not enough unallocated space for allocating a new data block group;

3) The extents in the target file range are not shared, neither through snapshots nor through reflinks.

This is wrong because a NOCOW write can be done in such case, and in fact it's possible to do it using a buffered IO write, since when failing to allocate data space, the buffered IO path checks if a NOCOW write is possible.

The failure in direct IO write path comes from the fact that early on, at btrfs_dio_iomap_begin(), we try to allocate data space for the write and if it that fails we return the error and stop - we never check if we can do NOCOW. But later, at btrfs_get_blocks_direct_write(), we check if we can do a NOCOW write into the range, or a subset of the range, and then release the previously reserved data space.

Fix this by doing the data reservation only if needed, when we must COW, at btrfs_get_blocks_direct_write() instead of doing it at btrfs_dio_iomap_begin(). This also simplifies a bit the logic and removes the inneficiency of doing unnecessary data reservations.

The following example test script reproduces the problem:

$ cat dio-nocow-enospc.sh #!/bin/bash

DEV=/dev/sdj MNT=/mnt/sdj

# Use a small fixed size (1G) filesystem so that it's quick to fill # it up. # Make sure the mixed block groups feature is not enabled because we # later want to not have more space available for allocating data # extents but still have enough metadata space free for the file writes. mkfs.btrfs -f -b $((1024 * 1024 * 1024)) -O ^mixed-bg $DEV mount $DEV $MNT

# Create our test file with the NOCOW attribute set. touch $MNT/foobar chattr +C $MNT/foobar

# Now fill in all unallocated space with data for our test file. # This will allocate a data block group that will be full and leave # no (or a very small amount of) unallocated space in the device, so # that it will not be possible to allocate a new block group later. echo echo "Creating test file with initial data..." xfs_io -c "pwrite -S 0xab -b 1M 0 900M" $MNT/foobar

# Now try a direct IO write against file range [0, 10M[. # This should succeed since this is a NOCOW file and an extent for the # range was previously allocated. echo echo "Trying direct IO write over allocated space..." xfs_io -d -c "pwrite -S 0xcd -b 10M 0 10M" $MNT/foobar

umount $MNT

When running the test:

$ ./dio-nocow-enospc.sh (...)

Creating test file with initial data... wrote 943718400/943718400 bytes at offset 0 900 MiB, 900 ops; 0:00:01.43 (625.526 MiB/sec and 625.5265 ops/sec)

Trying direct IO write over allocated space... pwrite: No space left on device

A test case for fstests will follow, testing both this direct IO write scenario as well as the buffered IO write scenario to make it less likely to get future regressions on the buffered IO case.

Reviewed-by: Josef Bacik josef@toxicpanda.com Signed-off-by: Filipe Manana fdmanana@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Anand Jain anand.jain@oracle.com --- fs/btrfs/inode.c | 142 ++++++++++++++++++++++++++--------------------- 1 file changed, 78 insertions(+), 64 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index e92f0b0afe9e..58053b5f0ce1 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -60,8 +60,6 @@ struct btrfs_iget_args { };

struct btrfs_dio_data { - u64 reserve; - loff_t length; ssize_t submitted; struct extent_changeset *data_reserved; }; @@ -7763,6 +7761,10 @@ static int btrfs_get_blocks_direct_write(struct extent_map **map, { struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb); struct extent_map *em = *map; + int type; + u64 block_start, orig_start, orig_block_len, ram_bytes; + bool can_nocow = false; + bool space_reserved = false; int ret = 0;

/* @@ -7777,9 +7779,6 @@ static int btrfs_get_blocks_direct_write(struct extent_map **map, if (test_bit(EXTENT_FLAG_PREALLOC, &em->flags) || ((BTRFS_I(inode)->flags & BTRFS_INODE_NODATACOW) && em->block_start != EXTENT_MAP_HOLE)) { - int type; - u64 block_start, orig_start, orig_block_len, ram_bytes; - if (test_bit(EXTENT_FLAG_PREALLOC, &em->flags)) type = BTRFS_ORDERED_PREALLOC; else @@ -7789,53 +7788,92 @@ static int btrfs_get_blocks_direct_write(struct extent_map **map,

if (can_nocow_extent(inode, start, &len, &orig_start, &orig_block_len, &ram_bytes, false) == 1 && - btrfs_inc_nocow_writers(fs_info, block_start)) { - struct extent_map *em2; + btrfs_inc_nocow_writers(fs_info, block_start)) + can_nocow = true; + }

- em2 = btrfs_create_dio_extent(BTRFS_I(inode), start, len, - orig_start, block_start, - len, orig_block_len, - ram_bytes, type); + 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); + if (ret < 0) { + /* Our caller expects us to free the input extent map. */ + free_extent_map(em); + *map = NULL; btrfs_dec_nocow_writers(fs_info, block_start); - if (type == BTRFS_ORDERED_PREALLOC) { - free_extent_map(em); - *map = em = em2; - } + goto out; + } + space_reserved = true;

- if (em2 && IS_ERR(em2)) { - ret = PTR_ERR(em2); - goto out; - } - /* - * For inode marked NODATACOW or extent marked PREALLOC, - * use the existing or preallocated extent, so does not - * need to adjust btrfs_space_info's bytes_may_use. - */ - btrfs_free_reserved_data_space_noquota(fs_info, len); - goto skip_cow; + em2 = btrfs_create_dio_extent(BTRFS_I(inode), start, len, + orig_start, block_start, + len, orig_block_len, + ram_bytes, type); + btrfs_dec_nocow_writers(fs_info, block_start); + if (type == BTRFS_ORDERED_PREALLOC) { + free_extent_map(em); + *map = em = em2; } - }

- /* this will cow the extent */ - free_extent_map(em); - *map = em = btrfs_new_extent_direct(BTRFS_I(inode), start, len); - if (IS_ERR(em)) { - ret = PTR_ERR(em); - goto out; + if (IS_ERR(em2)) { + ret = PTR_ERR(em2); + goto out; + } + } else { + const u64 prev_len = len; + + /* Our caller expects us to free the input extent map. */ + free_extent_map(em); + *map = NULL; + + /* We have to COW, so need to reserve metadata and data space. */ + ret = btrfs_delalloc_reserve_space(BTRFS_I(inode), + &dio_data->data_reserved, + start, len); + if (ret < 0) + goto out; + space_reserved = true; + + em = btrfs_new_extent_direct(BTRFS_I(inode), 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_space(BTRFS_I(inode), + dio_data->data_reserved, + start + len, prev_len - len, + true); }

- len = min(len, em->len - (start - em->start)); + /* + * We have created our ordered extent, so we can now release our reservation + * for an outstanding extent. + */ + btrfs_delalloc_release_extents(BTRFS_I(inode), len);

-skip_cow: /* * 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); - - dio_data->reserve -= len; out: + if (ret && space_reserved) { + btrfs_delalloc_release_extents(BTRFS_I(inode), len); + if (can_nocow) { + btrfs_delalloc_release_metadata(BTRFS_I(inode), len, true); + } else { + btrfs_delalloc_release_space(BTRFS_I(inode), + dio_data->data_reserved, + start, len, true); + extent_changeset_free(dio_data->data_reserved); + dio_data->data_reserved = NULL; + } + } return ret; }

@@ -7877,18 +7915,6 @@ static int btrfs_dio_iomap_begin(struct inode *inode, loff_t start, if (!dio_data) return -ENOMEM;

- dio_data->length = length; - if (write) { - dio_data->reserve = round_up(length, fs_info->sectorsize); - ret = btrfs_delalloc_reserve_space(BTRFS_I(inode), - &dio_data->data_reserved, - start, dio_data->reserve); - if (ret) { - extent_changeset_free(dio_data->data_reserved); - kfree(dio_data); - return ret; - } - } iomap->private = dio_data;

@@ -7981,14 +8007,8 @@ static int btrfs_dio_iomap_begin(struct inode *inode, loff_t start, unlock_extent_cached(&BTRFS_I(inode)->io_tree, lockstart, lockend, &cached_state); err: - if (dio_data) { - btrfs_delalloc_release_space(BTRFS_I(inode), - dio_data->data_reserved, start, - dio_data->reserve, true); - btrfs_delalloc_release_extents(BTRFS_I(inode), dio_data->reserve); - extent_changeset_free(dio_data->data_reserved); - kfree(dio_data); - } + kfree(dio_data); + return ret; }

@@ -8018,14 +8038,8 @@ static int btrfs_dio_iomap_end(struct inode *inode, loff_t pos, loff_t length, ret = -ENOTBLK; }

- if (write) { - if (dio_data->reserve) - btrfs_delalloc_release_space(BTRFS_I(inode), - dio_data->data_reserved, pos, - dio_data->reserve, true); - btrfs_delalloc_release_extents(BTRFS_I(inode), dio_data->length); + if (write) extent_changeset_free(dio_data->data_reserved); - } out: kfree(dio_data); iomap->private = NULL;