Re: [PATCH 07/10] libxfs: fix buftarg initialization for the RT device

["Darrick J. Wong" <djwong@kernel.org>]

On Fri, Sep 25, 2026 at 07:12:53AM +0200, Christoph Hellwig wrote:
> libxfs_buftarg_init currently sets the rtdev targp to the ddev one when
> no explicit RT device is provided, which allows tools like repair to
> proceed without a specified RT device when they should not, and
> potentially can cause data corruption.
> 
> Fix this by delaying the RT buftarg initialization to libxfs_mount,
> where we can check if the superblock indicates an internal RT device.
> This works because all external callers of libxfs_buftarg_init never
> need the RT device as they just examine the sb and/or log,
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

😬😬😬
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

> ---
>  libxfs/init.c | 11 +++++------
>  1 file changed, 5 insertions(+), 6 deletions(-)
> 
> diff --git a/libxfs/init.c b/libxfs/init.c
> index 842a2e1e09a9..97c5286c00a9 100644
> --- a/libxfs/init.c
> +++ b/libxfs/init.c
> @@ -554,8 +554,7 @@ libxfs_buftarg_reinit(
>  	}
>  
>  	if (mp->m_rtdev_targp && mp->m_rtdev_targp != mp->m_ddev_targp) {
> -		if ((xi->rt.dev && xi->rt.dev == xi->data.dev) ||
> -		    mp->m_rtdev_targp->bt_bdev != xi->rt.dev ||
> +		if (mp->m_rtdev_targp->bt_bdev != xi->rt.dev ||
>  		    mp->m_rtdev_targp->bt_mount != mp) {
>  			fprintf(stderr,
>  				_("%s: bad buftarg reinit, rtdev\n"),
> @@ -587,10 +586,6 @@ libxfs_buftarg_init(
>  		mp->m_logdev_targp = mp->m_ddev_targp;
>  	else
>  		mp->m_logdev_targp = libxfs_buftarg_alloc(mp, xi, &xi->log);
> -	if (!xi->rt.dev || xi->rt.dev == xi->data.dev)
> -		mp->m_rtdev_targp = mp->m_ddev_targp;
> -	else
> -		mp->m_rtdev_targp = libxfs_buftarg_alloc(mp, xi, &xi->rt);
>  }
>  
>  /* Compute maximum possible height for per-AG btree types for this fs. */
> @@ -739,6 +734,10 @@ libxfs_mount(
>  	if (flags & LIBXFS_MOUNT_REPORT_CORRUPTION)
>  		xfs_set_reporting_corruption(mp);
>  	libxfs_buftarg_init(mp, xi);
> +	if (sb->sb_rtstart)
> +		mp->m_rtdev_targp = mp->m_ddev_targp;
> +	else if (xi->rt.dev)
> +		mp->m_rtdev_targp = libxfs_buftarg_alloc(mp, xi, &xi->rt);
>  	libxfs_setup_write_error_injection(mp);
>  
>  	if (xi->data.name)
> -- 
> 2.53.0
> 
>