Re: [PATCH] Btrfs: fix metadata space leak on fixup worker failure to set range as delalloc

[David Sterba <dsterba@suse.cz>]

On Wed, Oct 09, 2019 at 05:43:59PM +0100, fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
> 
> In the fixup worker, if we fail to mark the range as delalloc in the io
> tree, we must release the previously reserved metadata, as well as update
> the outstanding extents counter for the inode, otherwise we leak metadata
> space.
> 
> In pratice we can't return an error from btrfs_set_extent_delalloc(),
> which is just a wrapper around __set_extent_bit(), as for most errors
> __set_extent_bit() does a BUG_ON() (or panics which hits a BUG_ON() as
> well) and returning an -EEXIST error doesn't happen in this case since
> the exclusive bits parameter always has a value of 0 through this code
> path. Nevertheless, just fix the error handling in the fixup worker,
> in case one day __set_extent_bit() can return an error to this code
> path.
> 
> Fixes: f3038ee3a3f101 ("btrfs: Handle btrfs_set_extent_delalloc failure in fixup worker")
> Signed-off-by: Filipe Manana <fdmanana@suse.com>

Added to misc-next, thanks.

> @@ -2201,12 +2201,16 @@ static void btrfs_writepage_fixup_worker(struct btrfs_work *work)
>  		mapping_set_error(page->mapping, ret);
>  		end_extent_writepage(page, ret, page_start, page_end);
>  		ClearPageChecked(page);
> -		goto out;
> +		goto out_reserved;
>  	}
>  
>  	ClearPageChecked(page);
>  	set_page_dirty(page);
> -	btrfs_delalloc_release_extents(BTRFS_I(inode), PAGE_SIZE, false);
> +out_reserved:
> +	btrfs_delalloc_release_extents(BTRFS_I(inode), PAGE_SIZE, ret != 0);

This is a shortcut to avoid extra variable to track the status of the
3rd parameter (qgroup_free) but as the goto and label are only a few
lines apart, I guess it's ok.

> +	if (ret)
> +		btrfs_delalloc_release_space(inode, data_reserved, page_start,
> +					     PAGE_SIZE, true);