On Tue, Oct 12, 2021 at 04:32:55PM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@xxxxxxxxxx>
>
> Reorganize struct xchk_btree so that we can dynamically size the context
> structure to fit the type of btree cursor that we have. This will
> enable us to use memory more efficiently once we start adding very tall
> btree types. Right-size the lastkey array so that we stop wasting the
> first array element.
"right size"?
I'm assuming this is the "nlevels - 1" bit?
>
> Signed-off-by: Darrick J. Wong <djwong@xxxxxxxxxx>
> ---
> fs/xfs/scrub/btree.c | 23 ++++++++++++-----------
> fs/xfs/scrub/btree.h | 11 ++++++++++-
> 2 files changed, 22 insertions(+), 12 deletions(-)
>
>
> diff --git a/fs/xfs/scrub/btree.c b/fs/xfs/scrub/btree.c
> index d5e1ca521fc4..6d4eba85ef77 100644
> --- a/fs/xfs/scrub/btree.c
> +++ b/fs/xfs/scrub/btree.c
> @@ -189,9 +189,9 @@ xchk_btree_key(
>
> /* If this isn't the first key, are they in order? */
> if (cur->bc_ptrs[level] > 1 &&
> - !cur->bc_ops->keys_inorder(cur, &bs->lastkey[level], key))
> + !cur->bc_ops->keys_inorder(cur, &bs->lastkey[level - 1], key))
> xchk_btree_set_corrupt(bs->sc, cur, level);
> - memcpy(&bs->lastkey[level], key, cur->bc_ops->key_len);
> + memcpy(&bs->lastkey[level - 1], key, cur->bc_ops->key_len);
>
> if (level + 1 >= cur->bc_nlevels)
> return;
> @@ -631,17 +631,24 @@ xchk_btree(
> union xfs_btree_ptr *pp;
> union xfs_btree_rec *recp;
> struct xfs_btree_block *block;
> - int level;
> struct xfs_buf *bp;
> struct check_owner *co;
> struct check_owner *n;
> + size_t cur_sz;
> + int level;
> int error = 0;
>
> /*
> * Allocate the btree scrub context from the heap, because this
> - * structure can get rather large.
> + * structure can get rather large. Don't let a caller feed us a
> + * totally absurd size.
> */
> - bs = kmem_zalloc(sizeof(struct xchk_btree), KM_NOFS | KM_MAYFAIL);
> + cur_sz = xchk_btree_sizeof(cur->bc_nlevels);
> + if (cur_sz > PAGE_SIZE) {
> + xchk_btree_set_corrupt(sc, cur, 0);
> + return 0;
> + }
> + bs = kmem_zalloc(cur_sz, KM_NOFS | KM_MAYFAIL);
> if (!bs)
> return -ENOMEM;
> bs->cur = cur;
> @@ -653,12 +660,6 @@ xchk_btree(
> /* Initialize scrub state */
> INIT_LIST_HEAD(&bs->to_check);
>
> - /* Don't try to check a tree with a height we can't handle. */
> - if (cur->bc_nlevels > XFS_BTREE_MAXLEVELS) {
> - xchk_btree_set_corrupt(sc, cur, 0);
> - goto out;
> - }
> -
> /*
> * Load the root of the btree. The helper function absorbs
> * error codes for us.
> diff --git a/fs/xfs/scrub/btree.h b/fs/xfs/scrub/btree.h
> index 7671108f9f85..62c3091ef20f 100644
> --- a/fs/xfs/scrub/btree.h
> +++ b/fs/xfs/scrub/btree.h
> @@ -39,9 +39,18 @@ struct xchk_btree {
>
> /* internal scrub state */
> union xfs_btree_rec lastrec;
> - union xfs_btree_key lastkey[XFS_BTREE_MAXLEVELS];
> struct list_head to_check;
> +
> + /* this element must come last! */
> + union xfs_btree_key lastkey[];
> };
> +
> +static inline size_t
> +xchk_btree_sizeof(unsigned int nlevels)
> +{
> + return struct_size((struct xchk_btree *)NULL, lastkey, nlevels - 1);
> +}
I'd like a comment here indicating that the max number of keys is
"nlevels - 1" because the last level of the tree is records and
that's held in a separate lastrec field...
That way there's a reminder of why there's a "- 1" here without
having work it out from first principles every time we look at this
code...
Otherwise it seems reasonable.
Cheers,
Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx
