Re: [PATCH V11 05/14] xfs: Check for extent overflow when adding/removing dir entries

Darrick J. Wong
2020-12-03T19:05:13Z

On Tue, Nov 17, 2020 at 07:14:07PM +0530, Chandan Babu R wrote:
> Directory entry addition/removal can cause the following,
> 1. Data block can be added/removed.
> A new extent can cause extent count to increase by 1.
> 2. Free disk block can be added/removed.
> Same behaviour as described above for Data block.
> 3. Dabtree blocks.
> XFS_DA_NODE_MAXDEPTH blocks can be added. Each of these
> can be new extents. Hence extent count can increase by
> XFS_DA_NODE_MAXDEPTH.
>
> To be able to always remove an existing directory entry, when adding a
> new directory entry we make sure to reserve inode fork extent count
> required for removing a directory entry in addition to that required for
> the directory entry add operation.
>
> Signed-off-by: Chandan Babu R <chandanrlinux@gmail.com>
> ---
> fs/xfs/libxfs/xfs_inode_fork.h | 13 +++++++++++++
> fs/xfs/xfs_inode.c | 27 +++++++++++++++++++++++++++
> fs/xfs/xfs_symlink.c | 5 +++++
> 3 files changed, 45 insertions(+)
>
> diff --git a/fs/xfs/libxfs/xfs_inode_fork.h b/fs/xfs/libxfs/xfs_inode_fork.h
> index 5de2f07d0dd5..fd93fdc67ee4 100644
> --- a/fs/xfs/libxfs/xfs_inode_fork.h
> +++ b/fs/xfs/libxfs/xfs_inode_fork.h
> @@ -57,6 +57,19 @@ struct xfs_ifork {
> #define XFS_IEXT_ATTR_MANIP_CNT(rmt_blks) \
> (XFS_DA_NODE_MAXDEPTH + max(1, rmt_blks))
>
> +/*
> + * Directory entry addition/removal can cause the following,
> + * 1. Data block can be added/removed.
> + * A new extent can cause extent count to increase by 1.
> + * 2. Free disk block can be added/removed.
> + * Same behaviour as described above for Data block.
> + * 3. Dabtree blocks.
> + * XFS_DA_NODE_MAXDEPTH blocks can be added. Each of these can be new
> + * extents. Hence extent count can increase by XFS_DA_NODE_MAXDEPTH.
> + */
> +#define XFS_IEXT_DIR_MANIP_CNT(mp) \
> + ((XFS_DA_NODE_MAXDEPTH + 1 + 1) * (mp)->m_dir_geo->fsbcount)
> +
> /*
> * Fork handling.
> */
> diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> index 2bfbcf28b1bd..f7b0b7fce940 100644
> --- a/fs/xfs/xfs_inode.c
> +++ b/fs/xfs/xfs_inode.c
> @@ -1177,6 +1177,11 @@ xfs_create(
> if (error)
> goto out_trans_cancel;
>
> + error = xfs_iext_count_may_overflow(dp, XFS_DATA_FORK,
> + XFS_IEXT_DIR_MANIP_CNT(mp) << 1);

Er, why did these double since V10? We're only adding one entry, right?

> + if (error)
> + goto out_trans_cancel;
> +
> /*
> * A newly created regular or special file just has one directory
> * entry pointing to them, but a directory also the "." entry
> @@ -1393,6 +1398,11 @@ xfs_link(
> xfs_trans_ijoin(tp, sip, XFS_ILOCK_EXCL);
> xfs_trans_ijoin(tp, tdp, XFS_ILOCK_EXCL);
>
> + error = xfs_iext_count_may_overflow(tdp, XFS_DATA_FORK,
> + XFS_IEXT_DIR_MANIP_CNT(mp) << 1);

Same question here.

> + if (error)
> + goto error_return;
> +
> /*
> * If we are using project inheritance, we only allow hard link
> * creation in our tree when the project IDs are the same; else
> @@ -2861,6 +2871,11 @@ xfs_remove(
> xfs_trans_ijoin(tp, dp, XFS_ILOCK_EXCL);
> xfs_trans_ijoin(tp, ip, XFS_ILOCK_EXCL);
>
> + error = xfs_iext_count_may_overflow(dp, XFS_DATA_FORK,
> + XFS_IEXT_DIR_MANIP_CNT(mp));
> + if (error)
> + goto out_trans_cancel;
> +
> /*
> * If we're removing a directory perform some additional validation.
> */
> @@ -3221,6 +3236,18 @@ xfs_rename(
> if (wip)
> xfs_trans_ijoin(tp, wip, XFS_ILOCK_EXCL);
>
> + error = xfs_iext_count_may_overflow(src_dp, XFS_DATA_FORK,
> + XFS_IEXT_DIR_MANIP_CNT(mp));
> + if (error)
> + goto out_trans_cancel;
> +
> + if (target_ip == NULL) {
> + error = xfs_iext_count_may_overflow(target_dp, XFS_DATA_FORK,
> + XFS_IEXT_DIR_MANIP_CNT(mp) << 1);

Why did this change to "<< 1" since V10?

I'm sorry, but I've lost my recollection on how the accounting works
here. This seems (to me anyway ;)) a good candidate for a comment:

For a rename within the same dir where target_name doesn't yet exist, we
are removing a name and then adding a name. We therefore check for iext
overflow with (DIR_MANIP_CNT * 2), right? And I think that "target name
does not exist" is synonymous with target_ip == NULL?

For a rename between dirs where the target name doesn't exist, we're
removing src_name from src_dp and adding target_name to target_dp.
Therefore we have to check for DIR_MANIP_CNT overflow on each of src_dp
and target_dp, right?

For a rename where target_name /does/ exist, we're only removing the
src_name, so we have to check for DIR_MANIP_CNT on src_dp, right?

For a RENAME_EXCHANGE we're not removing either name, so we don't need
to check for iext overflow of src_dp or target_dp, right?

> + if (error)
> + goto out_trans_cancel;
> + }
> +
> /*
> * If we are using project inheritance, we only allow renames
> * into our tree when the project IDs are the same; else the
> diff --git a/fs/xfs/xfs_symlink.c b/fs/xfs/xfs_symlink.c
> index 8e88a7ca387e..08aa808fe290 100644
> --- a/fs/xfs/xfs_symlink.c
> +++ b/fs/xfs/xfs_symlink.c
> @@ -220,6 +220,11 @@ xfs_symlink(
> if (error)
> goto out_trans_cancel;
>
> + error = xfs_iext_count_may_overflow(dp, XFS_DATA_FORK,
> + XFS_IEXT_DIR_MANIP_CNT(mp) << 1);

Same question as xfs_create.

--D

> + if (error)
> + goto out_trans_cancel;
> +
> /*
> * Allocate an inode for the symlink.
> */
> --
> 2.28.0
>