[PATCH] xfs: get new buffer for secondary superblocks from the first new AG

[Dave Chinner]

On Thu, Mar 21, 2013 at 12:12:51PM +0800, Jeff Liu wrote:
> In growfs operation, the unused parts of superblocks in the latest old AG are
> zero filled, hence we can safely read the secondary superblock buffer of it
> rather than getting a new buffer for it again.

>From the code:

	oagcount = mp->m_sb.sb_agcount;

And because the AG indexes are zero numbered, the index of the
last original AGs is (oagcount - 1). Hence we shoul donly be reading
from the AG headers if the current AG index is less than oagcount.

> This is a small refinement for commits 1375cb65.
> 
> Cc: Dave Chinner <david at fromorbit.com>
> Signed-off-by: Jie Liu <jeff.liu at oracle.com>
> ---
>  fs/xfs/xfs_fsops.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
> index 94eaeed..7d435dd 100644
> --- a/fs/xfs/xfs_fsops.c
> +++ b/fs/xfs/xfs_fsops.c
> @@ -449,7 +449,7 @@ xfs_growfs_data_private(
>  		 * disk as the contents of the new area we are growing into is
>  		 * completely unknown.
>  		 */
> -		if (agno < oagcount) {
> +		if (agno <= oagcount) {

With this change, when agno == oagcount we are one AG beyond the
original filesystem size and so if we read that space, we are
reading uninitialised data.

AFAICT, the current code is correct...

Cheers,

Dave.
-- 
Dave Chinner
david at fromorbit.com