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Re: [PATCH 4/3] xfs: don't assert on delalloc regions beyond EOF

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH 4/3] xfs: don't assert on delalloc regions beyond EOF
From: Ben Myers <bpm@xxxxxxx>
Date: Tue, 8 May 2012 12:26:12 -0500
Cc: xfs@xxxxxxxxxxx
In-reply-to: <20120429111617.GS9541@dastard>
References: <1335519922-14371-1-git-send-email-david@xxxxxxxxxxxxx> <20120429111617.GS9541@dastard>
User-agent: Mutt/1.5.20 (2009-06-14)
On Sun, Apr 29, 2012 at 09:16:17PM +1000, Dave Chinner wrote:
> 
> From: Dave Chinner <dchinner@xxxxxxxxxx>
> 
> When we are doing speculative delayed allocation beyond EOF,
> conversion of the region allocated beyond EOF is dependent on the
> largest free space extent available. If the largest free extent is
> smaller than the delalloc range, then after allocation we leave
> a delalloc extent that starts beyond EOF. This extent cannot *ever*
> be converted by flushing data, and so will remain there until either
> the EOF moves into the extent or it is truncated away.
> 
> Hence if xfs_getbmap() runs on such an inode and is asked to return
> extents beyond EOF, it will assert fail on this extent even though
> there is nothing xfs_getbmap() can do to convert it to a real
> extent. Hence we should simply report these delalloc extents rather
> than assert that there should be none.
> 
> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> ---
>  fs/xfs/xfs_bmap.c |   16 ++++++++++++++--
>  1 file changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/xfs/xfs_bmap.c b/fs/xfs/xfs_bmap.c
> index 26ab256..478bce9 100644
> --- a/fs/xfs/xfs_bmap.c
> +++ b/fs/xfs/xfs_bmap.c
> @@ -5620,8 +5620,20 @@ xfs_getbmap(
>                               XFS_FSB_TO_BB(mp, map[i].br_blockcount);
>                       out[cur_ext].bmv_unused1 = 0;
>                       out[cur_ext].bmv_unused2 = 0;
> -                     ASSERT(((iflags & BMV_IF_DELALLOC) != 0) ||
> -                           (map[i].br_startblock != DELAYSTARTBLOCK));
> +
> +                     /*
> +                      * delayed allocation extents that start beyond EOF can
> +                      * occur due to speculative EOF allocation when the
> +                      * delalloc extent is larger than the largest freespace
> +                      * extent at conversion time. These extents cannot be
> +                      * converted by data writeback, so can exist here even
> +                      * if we are not supposed to be finding delalloc
> +                      * extents.
> +                      */
> +                     if (map[i].br_startblock == DELAYSTARTBLOCK &&
> +                         map[i].br_startoff <= XFS_B_TO_FSB(mp, 
> XFS_ISIZE(ip)))
> +                             ASSERT((iflags & BMV_IF_DELALLOC) != 0);
> +

Looks fine.  This assert will no longer kick off for delay extents after eof,
but will still catch any within the file.

Reviewed-by: Ben Myers <bpm@xxxxxxx>

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