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btrfs: block-group: fix free-space bitmap threshold 

[BUG]
After commit 9afc66498a ("btrfs: block-group: refactor how we read one
block group item"), cache->length is being assigned after calling
btrfs_create_block_group_cache. This causes a problem since
set_free_space_tree_thresholds calculates the free-space threshold to
decide if the free-space tree should convert from extents to bitmaps.

The current code calls set_free_space_tree_thresholds with cache->length
being 0, which then makes cache->bitmap_high_thresh zero. This implies
the system will always use bitmap instead of extents, which is not
desired if the block group is not fragmented.

This behavior can be seen by a test that expects to repair systems
with FREE_SPACE_EXTENT and FREE_SPACE_BITMAP, but the current code only
created FREE_SPACE_BITMAP.

[FIX]
Call set_free_space_tree_thresholds after setting cache->length. There
is now a WARN_ON in set_free_space_tree_thresholds to help preventing
the same mistake to happen again in the future.

Link: https://github.com/kdave/btrfs-progs/issues/251
Fixes: 9afc66498a ("btrfs: block-group: refactor how we read one block group item")
CC: stable@vger.kernel.org # 5.8+
Reviewed-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Marcos Paulo de Souza <mpdesouza@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Marcos Paulo de Souza 2020-08-21 11:54:44 -03:00 committed by David Sterba
parent a84d5d429f
commit e3e39c72b9
2 changed files with 7 additions and 1 deletions
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4
fs/btrfs/block-group.c
View File

@ -1798,7 +1798,6 @@ static struct btrfs_block_group *btrfs_create_block_group_cache(
cache->fs_info = fs_info;
cache->full_stripe_len = btrfs_full_stripe_len(fs_info, start);
set_free_space_tree_thresholds(cache);
cache->discard_index = BTRFS_DISCARD_INDEX_UNUSED;
@ -1912,6 +1911,8 @@ static int read_one_block_group(struct btrfs_fs_info *info,
if (ret < 0)
goto error;
set_free_space_tree_thresholds(cache);
if (need_clear) {
/*
* When we mount with old space cache, we need to
@ -2132,6 +2133,7 @@ int btrfs_make_block_group(struct btrfs_trans_handle *trans, u64 bytes_used,
return -ENOMEM;
cache->length = size;
set_free_space_tree_thresholds(cache);
cache->used = bytes_used;
cache->flags = type;
cache->last_byte_to_unpin = (u64)-1;

4
fs/btrfs/free-space-tree.c
View File

@ -22,6 +22,10 @@ void set_free_space_tree_thresholds(struct btrfs_block_group *cache)
size_t bitmap_size;
u64 num_bitmaps, total_bitmap_size;
if (WARN_ON(cache->length == 0))
btrfs_warn(cache->fs_info, "block group %llu length is zero",
cache->start);
/*
* We convert to bitmaps when the disk space required for using extents
* exceeds that required for using bitmaps.