Re: [PATCH] btrfs: do not subtract delalloc from avail bytes

[Boris Burkov <boris@bur.io>]

On Fri, Jul 12, 2024 at 12:05:32AM +0900, Naohiro Aota wrote:
> The block group's avail bytes printed when dumping a space info subtract
> the delalloc_bytes. However, as shown in btrfs_add_reserved_bytes() and
> btrfs_free_reserved_bytes(), it is added or subtracted along with
> "reserved" for the delalloc case, which means the "delalloc_bytes" is a
> part of the "reserved" bytes. So, excluding it to calculate the avail space
> counts delalloc_bytes twice, which can lead to an invalid result.
> 
> Fixes: e50b122b832b ("btrfs: print available space for a block group when dumping a space info")
> CC: stable@vger.kernel.org # 6.6+
> Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>

Nice catch.
Reviewed-by: Boris Burkov <boris@bur.io>

> ---
>  fs/btrfs/space-info.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/fs/btrfs/space-info.c b/fs/btrfs/space-info.c
> index 9ac94d3119e8..c1d9d3664400 100644
> --- a/fs/btrfs/space-info.c
> +++ b/fs/btrfs/space-info.c
> @@ -583,8 +583,7 @@ void btrfs_dump_space_info(struct btrfs_fs_info *fs_info,
>  
>  		spin_lock(&cache->lock);
>  		avail = cache->length - cache->used - cache->pinned -
> -			cache->reserved - cache->delalloc_bytes -
> -			cache->bytes_super - cache->zone_unusable;
> +			cache->reserved - cache->bytes_super - cache->zone_unusable;
>  		btrfs_info(fs_info,
>  "block group %llu has %llu bytes, %llu used %llu pinned %llu reserved %llu delalloc %llu super %llu zone_unusable (%llu bytes available) %s",
>  			   cache->start, cache->length, cache->used, cache->pinned,
> -- 
> 2.45.2
>