Re: [PATCH V4 03/10] xfs: Check for extent overflow when punching a hole

Darrick J. Wong
2020-09-18T15:55:11Z

On Fri, Sep 18, 2020 at 03:17:52PM +0530, Chandan Babu R wrote:
> The extent mapping the file offset at which a hole has to be
> inserted will be split into two extents causing extent count to
> increase by 1.
>
> Signed-off-by: Chandan Babu R <chandanrlinux@gmail.com>
> ---
> fs/xfs/libxfs/xfs_inode_fork.h | 7 +++++++
> fs/xfs/xfs_bmap_item.c | 5 +++++
> fs/xfs/xfs_bmap_util.c | 10 ++++++++++
> 3 files changed, 22 insertions(+)
>
> diff --git a/fs/xfs/libxfs/xfs_inode_fork.h b/fs/xfs/libxfs/xfs_inode_fork.h
> index 7fc2b129a2e7..bcac769a7df6 100644
> --- a/fs/xfs/libxfs/xfs_inode_fork.h
> +++ b/fs/xfs/libxfs/xfs_inode_fork.h
> @@ -40,6 +40,13 @@ struct xfs_ifork {
> */
> #define XFS_IEXT_ADD_NOSPLIT_CNT (1)
>
> +/*
> + * Punching out an extent from the middle of an existing extent can cause the
> + * extent count to increase by 1.
> + * i.e. | Old extent | Hole | Old extent |
> + */
> +#define XFS_IEXT_PUNCH_HOLE_CNT (1)
> +
> /*
> * Fork handling.
> */
> diff --git a/fs/xfs/xfs_bmap_item.c b/fs/xfs/xfs_bmap_item.c
> index ec3691372e7c..5c7d08da8ff1 100644
> --- a/fs/xfs/xfs_bmap_item.c
> +++ b/fs/xfs/xfs_bmap_item.c
> @@ -519,6 +519,11 @@ xfs_bui_item_recover(
> }
> xfs_trans_ijoin(tp, ip, 0);
>
> + error = xfs_iext_count_may_overflow(ip, whichfork,
> + XFS_IEXT_PUNCH_HOLE_CNT);

I think this ought to be XFS_IEXT_ADD_NOSPLIT_CNT if bui_type is
XFS_BMAP_MAP and XFS_IEXT_PUNCH_HOLE_CNT if XFS_BMAP_UNMAP.

Whoever created the BUI should have called xfs_iext_count_may_overflow
before logging the BUI (and hence this should never occur) but it does
pay to be careful. :)

The rest of the logic in the patch looks ok.

--D

> + if (error)
> + goto err_inode;
> +
> count = bmap->me_len;
> error = xfs_trans_log_finish_bmap_update(tp, budp, type, ip, whichfork,
> bmap->me_startoff, bmap->me_startblock, &count, state);
> diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
> index dcd6e61df711..0776abd0103c 100644
> --- a/fs/xfs/xfs_bmap_util.c
> +++ b/fs/xfs/xfs_bmap_util.c
> @@ -891,6 +891,11 @@ xfs_unmap_extent(
>
> xfs_trans_ijoin(tp, ip, 0);
>
> + error = xfs_iext_count_may_overflow(ip, XFS_DATA_FORK,
> + XFS_IEXT_PUNCH_HOLE_CNT);
> + if (error)
> + goto out_trans_cancel;
> +
> error = xfs_bunmapi(tp, ip, startoffset_fsb, len_fsb, 0, 2, done);
> if (error)
> goto out_trans_cancel;
> @@ -1176,6 +1181,11 @@ xfs_insert_file_space(
> xfs_ilock(ip, XFS_ILOCK_EXCL);
> xfs_trans_ijoin(tp, ip, 0);
>
> + error = xfs_iext_count_may_overflow(ip, XFS_DATA_FORK,
> + XFS_IEXT_PUNCH_HOLE_CNT);
> + if (error)
> + goto out_trans_cancel;
> +
> /*
> * The extent shifting code works on extent granularity. So, if stop_fsb
> * is not the starting block of extent, we need to split the extent at
> --
> 2.28.0
>