Re: [PATCH 3/4] xfs: remove leftover CoW reservations when remounting ro

[Dave Chinner <david@fromorbit.com>]

On Fri, Dec 15, 2017 at 09:11:31AM -0800, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> When we're remounting the filesystem readonly, remove all CoW
> preallocations prior to going ro.  If the fs goes down after the ro
> remount, we never clean up the staging extents, which means xfs_check
> will trip over them on a subsequent run.  Practically speaking, the
> next mount will clean them up too, so this is unlikely to be seen.
> 
> Found by adding clonerange to fsstress and running xfs/017.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
>  fs/xfs/xfs_super.c |    8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> 
> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index f663022..7b6d150 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
> @@ -1369,6 +1369,14 @@ xfs_fs_remount(
>  
>  	/* rw -> ro */
>  	if (!(mp->m_flags & XFS_MOUNT_RDONLY) && (*flags & MS_RDONLY)) {
> +		/* Get rid of any leftover CoW reservations... */
> +		cancel_delayed_work_sync(&mp->m_cowblocks_work);
> +		error = xfs_icache_free_cowblocks(mp, NULL);
> +		if (error) {
> +			xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_INCORE);
> +			return error;
> +		}

On rw->ro do we start the m_cowblocks_work back up?

What about when we freeze the filesystem - shouldn't we clean
up the cow blocks there, too? We've tried hard in the past to make
freeze and rw->ro exactly the same so that if the system is powered
down while frozen it comes up almost entirely clean just like a
ro-remount in shutdown....

And, FWIW, this makes ro->rw and thaw essentially the same, too.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com