Re: [PATCH] xfs: growfs: don't read garbage for new secondary superblocks

[Carlos Maiolino <cmaiolino@redhat.com>]

On Mon, Oct 08, 2012 at 10:57:16PM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> When updating new secondary superblocks in a growfs operation, the
> sueprblock buffer is read from the newly grown region of the
> underlying device. This is not guaranteed to be zero, so violates
> the underlying assumption that the unused parts of superblocks are
> zero filled. Get a new buffer for these secondary superblocks to
> ensure that the unused regions are zero filled correctly.
> 
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
>  fs/xfs/xfs_fsops.c |   21 +++++++++++++++++++--
>  1 file changed, 19 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
> index c25b094..4beaede 100644
> --- a/fs/xfs/xfs_fsops.c
> +++ b/fs/xfs/xfs_fsops.c
> @@ -399,9 +399,26 @@ xfs_growfs_data_private(
>  
>  	/* update secondary superblocks. */
>  	for (agno = 1; agno < nagcount; agno++) {
> -		error = xfs_trans_read_buf(mp, NULL, mp->m_ddev_targp,
> +		error = 0;
> +		/*
> +		 * new secondary superblocks need to be zeroed, not read from
> +		 * disk as the contents of the new area we are growing into is
> +		 * completely unknown.
> +		 */
> +		if (agno < oagcount) {
> +			error = xfs_trans_read_buf(mp, NULL, mp->m_ddev_targp,
>  				  XFS_AGB_TO_DADDR(mp, agno, XFS_SB_BLOCK(mp)),
>  				  XFS_FSS_TO_BB(mp, 1), 0, &bp);
> +		} else {
> +			bp = xfs_trans_get_buf(NULL, mp->m_ddev_targp,
> +				  XFS_AGB_TO_DADDR(mp, agno, XFS_SB_BLOCK(mp)),
> +				  XFS_FSS_TO_BB(mp, 1), 0);
> +			if (bp)
> +				xfs_buf_zero(bp, 0, BBTOB(bp->b_length));
> +			else
> +				error = ENOMEM;
> +		}
> +
>  		if (error) {
>  			xfs_warn(mp,
>  		"error %d reading secondary superblock for ag %d",
> @@ -423,7 +440,7 @@ xfs_growfs_data_private(
>  			break; /* no point in continuing */
>  		}
>  	}
> -	return 0;
> +	return error;
>  
>   error0:
>  	xfs_trans_cancel(tp, XFS_TRANS_ABORT);
> -- 
> 1.7.10
> 

Looks good.

Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>

-- 
--Carlos

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