Re: [PATCH] btrfs-progs: mkfs: set super_cache_generation to 0 if we're using free space tree

[Nikolay Borisov <nborisov@suse.com>]

On 31.07.21 г. 10:42, Qu Wenruo wrote:
> [HICCUP]
> There is a bug report that mkfs.btrfs -R free-space-tree still makes
> kernel to try to cleanup the v1 space cache:
> 
>   # mkfs.btrfs -R free-space-tree -f /dev/test/scratch1
>   # mount /dev/test/scratch1 /mnt/btrfs
>   # dmesg | grep cleaning
>   BTRFS info (device dm-6): cleaning free space cache v1
> 
> [CAUSE]
> By default, mkfs.btrfs will set super cache generation to (u64)-1, which
> will inform kernel that the v1 space cache is invalid, needs to
> regenerate it.
> 
> But for free space cache tree, kernel will set super cache generation to
> 0, to indicate v1 space cache is not in use.
> 
> This means, even we enabled free space tree with all the RO compatible
> bits and new tree, as long as super cache generation is not 0, kernel
> still consider the fs has some invalid v1 space cache, and will try to
> remove them.
> 
> [FIX]
> This is not a big deal, but to make the "-R free-space-tree" to really
> work as kernel, we also need to set super cache generation to 0.
> 
> Reported-by: Chris Murphy <lists@colorremedies.com>
> Link: https://lore.kernel.org/linux-btrfs/CAJCQCtSvgzyOnxtrqQZZirSycEHp+g0eDH5c+Kw9mW=PgxuXmw@mail.gmail.com/
> Signed-off-by: Qu Wenruo <wqu@suse.com>

Reviewed-by: Nikolay Borisov <nborisov@suse.com>

> ---
>  kernel-shared/free-space-tree.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/kernel-shared/free-space-tree.c b/kernel-shared/free-space-tree.c
> index 2edc7fc716f5..7f589dfef950 100644
> --- a/kernel-shared/free-space-tree.c
> +++ b/kernel-shared/free-space-tree.c
> @@ -1447,6 +1447,7 @@ int btrfs_create_free_space_tree(struct btrfs_fs_info *fs_info)
>  
>  	btrfs_set_fs_compat_ro(fs_info, FREE_SPACE_TREE);
>  	btrfs_set_fs_compat_ro(fs_info, FREE_SPACE_TREE_VALID);
> +	btrfs_set_super_cache_generation(fs_info->super_copy, 0);
>  
>  	ret = btrfs_commit_transaction(trans, tree_root);
>  	if (ret)
>