[PATCH 5.8 130/186] btrfs: block-group: fix free-space bitmap threshold

From: Greg Kroah-Hartman
Date: Tue Sep 08 2020 - 15:11:11 EST

From: Marcos Paulo de Souza <mpdesouza@xxxxxxxx>

commit e3e39c72b99f93bbd0420d38c858e7c4a061bb63 upstream.

After commit 9afc66498a0b ("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

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: 9afc66498a0b ("btrfs: block-group: refactor how we read one block group item")
CC: stable@xxxxxxxxxxxxxxx # 5.8+
Reviewed-by: Qu Wenruo <wqu@xxxxxxxx>
Reviewed-by: Filipe Manana <fdmanana@xxxxxxxx>
Signed-off-by: Marcos Paulo de Souza <mpdesouza@xxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

fs/btrfs/block-group.c | 4 +++-
fs/btrfs/free-space-tree.c | 4 ++++
2 files changed, 7 insertions(+), 1 deletion(-)

--- a/fs/btrfs/block-group.c
+++ b/fs/btrfs/block-group.c
@@ -1814,7 +1814,6 @@ static struct btrfs_block_group *btrfs_c

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;

@@ -1928,6 +1927,8 @@ static int read_one_block_group(struct b
if (ret < 0)
goto error;

+ set_free_space_tree_thresholds(cache);
if (need_clear) {
* When we mount with old space cache, we need to
@@ -2148,6 +2149,7 @@ int btrfs_make_block_group(struct btrfs_
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;
--- a/fs/btrfs/free-space-tree.c
+++ b/fs/btrfs/free-space-tree.c
@@ -22,6 +22,10 @@ void set_free_space_tree_thresholds(stru
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.