Re: [PATCH 5/7] btrfs: clear BTRFS_ROOT_DEAD_RELOC_TREE before dropping the reloc root

[David Sterba <dsterba@suse.cz>]

On Mon, Mar 02, 2020 at 01:47:55PM -0500, Josef Bacik wrote:
> We were doing the clear dance for the reloc root after doing the drop of
> the reloc root, which means we have a giant window where we could miss
> having BTRFS_ROOT_DEAD_RELOC_TREE unset and the reloc_root == NULL.
> 
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>
> ---
>  fs/btrfs/relocation.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
> index e60450c44406..acd21c156378 100644
> --- a/fs/btrfs/relocation.c
> +++ b/fs/btrfs/relocation.c
> @@ -2291,18 +2291,19 @@ static int clean_dirty_subvols(struct reloc_control *rc)
>  
>  			list_del_init(&root->reloc_dirty_list);
>  			root->reloc_root = NULL;
> -			if (reloc_root) {
> -
> -				ret2 = btrfs_drop_snapshot(reloc_root, NULL, 0, 1);
> -				if (ret2 < 0 && !ret)
> -					ret = ret2;
> -			}
>  			/*
>  			 * Need barrier to ensure clear_bit() only happens after
>  			 * root->reloc_root = NULL. Pairs with have_reloc_root.
>  			 */
>  			smp_wmb();
>  			clear_bit(BTRFS_ROOT_DEAD_RELOC_TREE, &root->state);
> +
> +			if (reloc_root) {
> +
> +				ret2 = btrfs_drop_snapshot(reloc_root, NULL, 0, 1);
> +				if (ret2 < 0 && !ret)
> +					ret = ret2;
> +			}

This reverts fix 1fac4a54374f7ef385938f3c6cf7649c0fe4f6cd that moved if
(reloc_root) before the clear_bit.