Re: [PATCH 2/3] btrfs: zoned: fix write time activation failure for metadata block group

[Damien Le Moal <dlemoal@kernel.org>]

On 7/7/25 11:44 AM, Naohiro Aota wrote:
> Since commit 13bb483d32ab ("btrfs: zoned: activate metadata block group on
> write time"), we activate a metadata block group on the write time. If the

on the write time -> at write time

> zone capacity is small enough, we can allocate the entire region before the
> first write. Then, we hit the btrfs_zoned_bg_is_full() in
> btrfs_zone_activate() and the activation fails.
> 
> For a data block group, we already check the fullness condition in the
> caller side. And, the fullness check is not necessary for metadata's
> write-time activation. Replace it with a proper WARN.

I am very confused by this explanation. If the BG is fully allocated before we
issue the first write, we still need to activate that BG, no ? So why the
WARN() ? That seems wrong to me. But I may not be understanding your
explanation, which means you need to clarify it :)

> 
> Fixes: 13bb483d32ab ("btrfs: zoned: activate metadata block group on write time")
> CC: stable@vger.kernel.org # 6.6+
> Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
> ---
>  fs/btrfs/zoned.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/btrfs/zoned.c b/fs/btrfs/zoned.c
> index 6fb4d95412d6..9c354e84ab07 100644
> --- a/fs/btrfs/zoned.c
> +++ b/fs/btrfs/zoned.c
> @@ -2169,10 +2169,13 @@ bool btrfs_zone_activate(struct btrfs_block_group *block_group)
>  		goto out_unlock;
>  	}
>  
> -	/* No space left */
> -	if (btrfs_zoned_bg_is_full(block_group)) {
> -		ret = false;
> -		goto out_unlock;
> +	if (block_group->flags & BTRFS_BLOCK_GROUP_DATA) {
> +		if (WARN_ON_ONCE(btrfs_zoned_bg_is_full(block_group))) {
> +			ret = false;
> +			goto out_unlock;
> +		}
> +	} else {
> +		WARN_ON_ONCE(block_group->meta_write_pointer != block_group->start);
>  	}
>  
>  	for (i = 0; i < map->num_stripes; i++) {


-- 
Damien Le Moal
Western Digital Research