[05/17] xfs: dynamically allocate btree scrub context structure

Commit Message

Darrick J. Wong Oct. 14, 2021, 8:17 p.m. UTC

From: Darrick J. Wong <[e-mail]>

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 to match the number of *node*
levels in the tree so that we stop wasting space.

Signed-off-by: Darrick J. Wong <[e-mail]>
---
 fs/xfs/scrub/btree.c |   23 ++++++++++++-----------
 fs/xfs/scrub/btree.h |   15 ++++++++++++++-
 2 files changed, 26 insertions(+), 12 deletions(-)

Comments

Dave Chinner Oct. 14, 2021, 10:48 p.m. UTC | #1

On Thu, Oct 14, 2021 at 01:17:22PM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <[e-mail]>
> 
> 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 to match the number of *node*
> levels in the tree so that we stop wasting space.
> 
> Signed-off-by: Darrick J. Wong <[e-mail]>
> ---
>  fs/xfs/scrub/btree.c |   23 ++++++++++++-----------
>  fs/xfs/scrub/btree.h |   15 ++++++++++++++-
>  2 files changed, 26 insertions(+), 12 deletions(-)

Looks good now.

Reviewed-by: Dave Chinner <[e-mail]>

Patch

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..da61a53a0b61 100644
--- a/fs/xfs/scrub/btree.h
+++ b/fs/xfs/scrub/btree.h
@@ -39,9 +39,22 @@  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[];
 };
+
+/*
+ * Calculate the size of a xchk_btree structure.  There are nlevels-1 slots for
+ * keys because we track leaf records separately in lastrec.
+ */
+static inline size_t
+xchk_btree_sizeof(unsigned int nlevels)
+{
+	return struct_size((struct xchk_btree *)NULL, lastkey, nlevels - 1);
+}
+
 int xchk_btree(struct xfs_scrub *sc, struct xfs_btree_cur *cur,
 		xchk_btree_rec_fn scrub_fn, const struct xfs_owner_info *oinfo,
 		void *private);