Re: [PATCH] btrfs: zoned: reset active_meta_bg on zone finish

On 7/3/26 10:45 AM, Johannes Thumshirn wrote:
> do_zone_finish() clears BLOCK_GROUP_FLAG_ZONE_IS_ACTIVE and removes the
> block group from zone_active_bgs, but only the path in
> check_bg_is_active() resets fs_info->active_meta_bg / active_system_bg.
> Any other finish path leaves active_meta_bg / active_system_bg pointing
> at an inactive, fully written block group.
>
> Reset the corresponding active_{meta,system}_bg pointer in do_zone_finish()
> so it can never go stale.
>
> Fixes: 13bb483d32ab ("btrfs: zoned: activate metadata block group on write time")
> Cc: [email protected]
> Signed-off-by: Johannes Thumshirn <[email protected]>
> ---
>   fs/btrfs/zoned.c | 15 +++++++++++++++
>   1 file changed, 15 insertions(+)
>
> diff --git a/fs/btrfs/zoned.c b/fs/btrfs/zoned.c
> index 44a13ed6b8b2..c8c850de1702 100644
> --- a/fs/btrfs/zoned.c
> +++ b/fs/btrfs/zoned.c
> @@ -2539,6 +2539,7 @@ static int do_zone_finish(struct btrfs_block_group *block_group, bool fully_writ
>   	const bool is_metadata = (block_group->flags &
>   			(BTRFS_BLOCK_GROUP_METADATA | BTRFS_BLOCK_GROUP_SYSTEM));
>   	struct btrfs_dev_replace *dev_replace = &fs_info->dev_replace;
> +	struct btrfs_block_group **active_bg = NULL;
>   	int ret = 0;
>   	int i;
>   
> @@ -2636,6 +2637,20 @@ static int do_zone_finish(struct btrfs_block_group *block_group, bool fully_writ
>   	/* For active_bg_list */
>   	btrfs_put_block_group(block_group);
>   
> +	if (block_group->flags & BTRFS_BLOCK_GROUP_SYSTEM)
> +		active_bg = &fs_info->active_system_bg;
> +	else if (block_group->flags & BTRFS_BLOCK_GROUP_METADATA)
> +		active_bg = &fs_info->active_meta_bg;
> +
> +	if (active_bg) {
> +		btrfs_zoned_meta_io_lock(fs_info);
> +		if (*active_bg == block_group) {
> +			btrfs_put_block_group(block_group);
> +			*active_bg = NULL;
> +		}
> +		btrfs_zoned_meta_io_unlock(fs_info);
> +	}
> +
>   	clear_and_wake_up_bit(BTRFS_FS_NEED_ZONE_FINISH, &fs_info->flags);
>   
>   	return 0;

I think Sashiko has a point here:

https://sashiko.dev/#/patchset/20260703084559.136605-1-johannes.thumshirn%40wdc.com

check_bg_is_active() should take a reference before calling into 
do_zone_finish() or actually clearing fs_info->active_{meta,system}_bg 
can even be done in check_bg_is_active() after calling do_zone_finish().

That'll then also eliminate Miquel's concerns.