Re: [PATCH V9.2] xfs: Directory's data fork extent counter can never overflow

Darrick J. Wong
2022-04-12T17:04:47Z

On Tue, Apr 12, 2022 at 07:32:37PM +0530, Chandan Babu R wrote:
> The maximum file size that can be represented by the data fork extent counter
> in the worst case occurs when all extents are 1 block in length and each block
> is 1KB in size.
>
> With XFS_MAX_EXTCNT_DATA_FORK_SMALL representing maximum extent count and with
> 1KB sized blocks, a file can reach upto,
> (2^31) * 1KB = 2TB
>
> This is much larger than the theoretical maximum size of a directory
> i.e. XFS_DIR2_SPACE_SIZE * 3 = ~96GB.
>
> Since a directory's inode can never overflow its data fork extent counter,
> this commit removes all the overflow checks associated with
> it. xfs_dinode_verify() now performs a rough check to verify if a diretory's
> data fork is larger than 96GB.
>
> Reviewed-by: Dave Chinner <dchinner@redhat.com>
> Signed-off-by: Chandan Babu R <chandan.babu@oracle.com>

Neato!
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D

> ---
> fs/xfs/libxfs/xfs_bmap.c | 20 -------------
> fs/xfs/libxfs/xfs_da_btree.h | 1 +
> fs/xfs/libxfs/xfs_da_format.h | 1 +
> fs/xfs/libxfs/xfs_dir2.c | 8 +++++
> fs/xfs/libxfs/xfs_format.h | 13 ++++++++
> fs/xfs/libxfs/xfs_inode_buf.c | 3 ++
> fs/xfs/libxfs/xfs_inode_fork.h | 13 --------
> fs/xfs/xfs_inode.c | 55 ++--------------------------------
> fs/xfs/xfs_symlink.c | 5 ----
> 9 files changed, 28 insertions(+), 91 deletions(-)
>
> diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
> index 1254d4d4821e..4fab0c92ab70 100644
> --- a/fs/xfs/libxfs/xfs_bmap.c
> +++ b/fs/xfs/libxfs/xfs_bmap.c
> @@ -5147,26 +5147,6 @@ xfs_bmap_del_extent_real(
> * Deleting the middle of the extent.
> */
>
> - /*
> - * For directories, -ENOSPC is returned since a directory entry
> - * remove operation must not fail due to low extent count
> - * availability. -ENOSPC will be handled by higher layers of XFS
> - * by letting the corresponding empty Data/Free blocks to linger
> - * until a future remove operation. Dabtree blocks would be
> - * swapped with the last block in the leaf space and then the
> - * new last block will be unmapped.
> - *
> - * The above logic also applies to the source directory entry of
> - * a rename operation.
> - */
> - error = xfs_iext_count_may_overflow(ip, whichfork, 1);
> - if (error) {
> - ASSERT(S_ISDIR(VFS_I(ip)->i_mode) &&
> - whichfork == XFS_DATA_FORK);
> - error = -ENOSPC;
> - goto done;
> - }
> -
> old = got;
>
> got.br_blockcount = del->br_startoff - got.br_startoff;
> diff --git a/fs/xfs/libxfs/xfs_da_btree.h b/fs/xfs/libxfs/xfs_da_btree.h
> index 0faf7d9ac241..7f08f6de48bf 100644
> --- a/fs/xfs/libxfs/xfs_da_btree.h
> +++ b/fs/xfs/libxfs/xfs_da_btree.h
> @@ -30,6 +30,7 @@ struct xfs_da_geometry {
> unsigned int free_hdr_size; /* dir2 free header size */
> unsigned int free_max_bests; /* # of bests entries in dir2 free */
> xfs_dablk_t freeblk; /* blockno of free data v2 */
> + xfs_extnum_t max_extents; /* Max. extents in corresponding fork */
>
> xfs_dir2_data_aoff_t data_first_offset;
> size_t data_entry_offset;
> diff --git a/fs/xfs/libxfs/xfs_da_format.h b/fs/xfs/libxfs/xfs_da_format.h
> index 5a49caa5c9df..95354b7ab7f5 100644
> --- a/fs/xfs/libxfs/xfs_da_format.h
> +++ b/fs/xfs/libxfs/xfs_da_format.h
> @@ -277,6 +277,7 @@ xfs_dir2_sf_firstentry(struct xfs_dir2_sf_hdr *hdr)
> * Directory address space divided into sections,
> * spaces separated by 32GB.
> */
> +#define XFS_DIR2_MAX_SPACES 3
> #define XFS_DIR2_SPACE_SIZE (1ULL << (32 + XFS_DIR2_DATA_ALIGN_LOG))
> #define XFS_DIR2_DATA_SPACE 0
> #define XFS_DIR2_DATA_OFFSET (XFS_DIR2_DATA_SPACE * XFS_DIR2_SPACE_SIZE)
> diff --git a/fs/xfs/libxfs/xfs_dir2.c b/fs/xfs/libxfs/xfs_dir2.c
> index 5f1e4799e8fa..3cd51fa3837b 100644
> --- a/fs/xfs/libxfs/xfs_dir2.c
> +++ b/fs/xfs/libxfs/xfs_dir2.c
> @@ -150,6 +150,8 @@ xfs_da_mount(
> dageo->freeblk = xfs_dir2_byte_to_da(dageo, XFS_DIR2_FREE_OFFSET);
> dageo->node_ents = (dageo->blksize - dageo->node_hdr_size) /
> (uint)sizeof(xfs_da_node_entry_t);
> + dageo->max_extents = (XFS_DIR2_MAX_SPACES * XFS_DIR2_SPACE_SIZE) >>
> + mp->m_sb.sb_blocklog;
> dageo->magicpct = (dageo->blksize * 37) / 100;
>
> /* set up attribute geometry - single fsb only */
> @@ -161,6 +163,12 @@ xfs_da_mount(
> dageo->node_hdr_size = mp->m_dir_geo->node_hdr_size;
> dageo->node_ents = (dageo->blksize - dageo->node_hdr_size) /
> (uint)sizeof(xfs_da_node_entry_t);
> +
> + if (xfs_has_large_extent_counts(mp))
> + dageo->max_extents = XFS_MAX_EXTCNT_ATTR_FORK_LARGE;
> + else
> + dageo->max_extents = XFS_MAX_EXTCNT_ATTR_FORK_SMALL;
> +
> dageo->magicpct = (dageo->blksize * 37) / 100;
> return 0;
> }
> diff --git a/fs/xfs/libxfs/xfs_format.h b/fs/xfs/libxfs/xfs_format.h
> index 82b404c99b80..43de892d0305 100644
> --- a/fs/xfs/libxfs/xfs_format.h
> +++ b/fs/xfs/libxfs/xfs_format.h
> @@ -915,6 +915,19 @@ enum xfs_dinode_fmt {
> *
> * Rounding up 47 to the nearest multiple of bits-per-byte results in 48. Hence
> * 2^48 was chosen as the maximum data fork extent count.
> + *
> + * The maximum file size that can be represented by the data fork extent counter
> + * in the worst case occurs when all extents are 1 block in length and each
> + * block is 1KB in size.
> + *
> + * With XFS_MAX_EXTCNT_DATA_FORK_SMALL representing maximum extent count and
> + * with 1KB sized blocks, a file can reach upto,
> + * 1KB * (2^31) = 2TB
> + *
> + * This is much larger than the theoretical maximum size of a directory
> + * i.e. XFS_DIR2_SPACE_SIZE * XFS_DIR2_MAX_SPACES = ~96GB.
> + *
> + * Hence, a directory inode can never overflow its data fork extent counter.
> */
> #define XFS_MAX_EXTCNT_DATA_FORK_LARGE ((xfs_extnum_t)((1ULL << 48) - 1))
> #define XFS_MAX_EXTCNT_ATTR_FORK_LARGE ((xfs_extnum_t)((1ULL << 32) - 1))
> diff --git a/fs/xfs/libxfs/xfs_inode_buf.c b/fs/xfs/libxfs/xfs_inode_buf.c
> index ee8d4eb7d048..74b82ec80f8e 100644
> --- a/fs/xfs/libxfs/xfs_inode_buf.c
> +++ b/fs/xfs/libxfs/xfs_inode_buf.c
> @@ -491,6 +491,9 @@ xfs_dinode_verify(
> if (mode && nextents + naextents > nblocks)
> return __this_address;
>
> + if (S_ISDIR(mode) && nextents > mp->m_dir_geo->max_extents)
> + return __this_address;
> +
> if (mode && XFS_DFORK_BOFF(dip) > mp->m_sb.sb_inodesize)
> return __this_address;
>
> diff --git a/fs/xfs/libxfs/xfs_inode_fork.h b/fs/xfs/libxfs/xfs_inode_fork.h
> index fd5c3c2d77e0..6f9d69f8896e 100644
> --- a/fs/xfs/libxfs/xfs_inode_fork.h
> +++ b/fs/xfs/libxfs/xfs_inode_fork.h
> @@ -39,19 +39,6 @@ struct xfs_ifork {
> */
> #define XFS_IEXT_PUNCH_HOLE_CNT (1)
>
> -/*
> - * Directory entry addition 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)
> -
> /*
> * Adding/removing an xattr can cause XFS_DA_NODE_MAXDEPTH extents to
> * be added. One extra extent for dabtree in case a local attr is
> diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> index adc1355ce853..20f15a0393e1 100644
> --- a/fs/xfs/xfs_inode.c
> +++ b/fs/xfs/xfs_inode.c
> @@ -1024,11 +1024,6 @@ xfs_create(
> xfs_ilock(dp, XFS_ILOCK_EXCL | XFS_ILOCK_PARENT);
> unlock_dp_on_error = true;
>
> - error = xfs_iext_count_may_overflow(dp, XFS_DATA_FORK,
> - XFS_IEXT_DIR_MANIP_CNT(mp));
> - 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
> @@ -1242,11 +1237,6 @@ xfs_link(
> if (error)
> goto std_return;
>
> - error = xfs_iext_count_may_overflow(tdp, XFS_DATA_FORK,
> - XFS_IEXT_DIR_MANIP_CNT(mp));
> - 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
> @@ -3210,35 +3200,6 @@ xfs_rename(
> /*
> * Check for expected errors before we dirty the transaction
> * so we can return an error without a transaction abort.
> - *
> - * Extent count overflow check:
> - *
> - * From the perspective of src_dp, a rename operation is essentially a
> - * directory entry remove operation. Hence the only place where we check
> - * for extent count overflow for src_dp is in
> - * xfs_bmap_del_extent_real(). xfs_bmap_del_extent_real() returns
> - * -ENOSPC when it detects a possible extent count overflow and in
> - * response, the higher layers of directory handling code do the
> - * following:
> - * 1. Data/Free blocks: XFS lets these blocks linger until a
> - * future remove operation removes them.
> - * 2. Dabtree blocks: XFS swaps the blocks with the last block in the
> - * Leaf space and unmaps the last block.
> - *
> - * For target_dp, there are two cases depending on whether the
> - * destination directory entry exists or not.
> - *
> - * When destination directory entry does not exist (i.e. target_ip ==
> - * NULL), extent count overflow check is performed only when transaction
> - * has a non-zero sized space reservation associated with it. With a
> - * zero-sized space reservation, XFS allows a rename operation to
> - * continue only when the directory has sufficient free space in its
> - * data/leaf/free space blocks to hold the new entry.
> - *
> - * When destination directory entry exists (i.e. target_ip != NULL), all
> - * we need to do is change the inode number associated with the already
> - * existing entry. Hence there is no need to perform an extent count
> - * overflow check.
> */
> if (target_ip == NULL) {
> /*
> @@ -3249,12 +3210,6 @@ xfs_rename(
> error = xfs_dir_canenter(tp, target_dp, target_name);
> if (error)
> goto out_trans_cancel;
> - } else {
> - error = xfs_iext_count_may_overflow(target_dp,
> - XFS_DATA_FORK,
> - XFS_IEXT_DIR_MANIP_CNT(mp));
> - if (error)
> - goto out_trans_cancel;
> }
> } else {
> /*
> @@ -3422,18 +3377,12 @@ xfs_rename(
> * inode number of the whiteout inode rather than removing it
> * altogether.
> */
> - if (wip) {
> + if (wip)
> error = xfs_dir_replace(tp, src_dp, src_name, wip->i_ino,
> spaceres);
> - } else {
> - /*
> - * NOTE: We don't need to check for extent count overflow here
> - * because the dir remove name code will leave the dir block in
> - * place if the extent count would overflow.
> - */
> + else
> error = xfs_dir_removename(tp, src_dp, src_name, src_ip->i_ino,
> spaceres);
> - }
>
> if (error)
> goto out_trans_cancel;
> diff --git a/fs/xfs/xfs_symlink.c b/fs/xfs/xfs_symlink.c
> index affbedf78160..4145ba872547 100644
> --- a/fs/xfs/xfs_symlink.c
> +++ b/fs/xfs/xfs_symlink.c
> @@ -226,11 +226,6 @@ xfs_symlink(
> goto out_trans_cancel;
> }
>
> - error = xfs_iext_count_may_overflow(dp, XFS_DATA_FORK,
> - XFS_IEXT_DIR_MANIP_CNT(mp));
> - if (error)
> - goto out_trans_cancel;
> -
> /*
> * Allocate an inode for the symlink.
> */
> --
> 2.30.2
>