From: Marcos Paulo de Souza <mpdesouza@suse.com>
Date: Fri, 21 Aug 2020 11:54:44 -0300
Git-commit: e3e39c72b99f93bbd0420d38c858e7c4a061bb63
Patch-mainline: 5.9-rc4
References: bsc#1176019
Subject: [PATCH] btrfs: block-group: fix free-space bitmap threshold
[BUG]
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
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: 9afc66498a0b ("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>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
---
fs/btrfs/block-group.c | 4 +++-
fs/btrfs/free-space-tree.c | 4 ++++
2 files changed, 7 insertions(+), 1 deletion(-)
diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
index 922618876..00a6315eb 100644
--- a/fs/btrfs/block-group.c
+++ b/fs/btrfs/block-group.c
@@ -1662,7 +1662,6 @@ 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);
atomic_set(&cache->count, 1);
spin_lock_init(&cache->lock);
@@ -1773,6 +1772,8 @@ 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
@@ -1988,6 +1989,7 @@ 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;
diff --git a/fs/btrfs/free-space-tree.c b/fs/btrfs/free-space-tree.c
index 8b1f5c889..6b9faf3b0 100644
--- a/fs/btrfs/free-space-tree.c
+++ b/fs/btrfs/free-space-tree.c
@@ -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.
--
2.26.2