Merge tag 'scrub-detect-refcount-gaps-6.4_2023-04-11' of git://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux into guilt/xfs-for-next

xfs: detect incorrect gaps in refcount btree [v24.5]

The next few patchsets address a deficiency in scrub that I found while
QAing the refcount btree scrubber.  If there's a gap between refcount
records, we need to cross-reference that gap with the reverse mappings
to ensure that there are no overlapping records in the rmap btree.  If
we find any, then the refcount btree is not consistent.  This is not a
property that is specific to the refcount btree; they all need to have
this sort of keyspace scanning logic to detect inconsistencies.

To do this accurately, we need to be able to scan the keyspace of a
btree (which we already do) to be able to tell the caller if the
keyspace is empty, sparse, or fully covered by records.  The first few
patches add the keyspace scanner to the generic btree code, along with
the ability to mask off parts of btree keys because when we scan the
rmapbt, we only care about space usage, not the owners.

The final patch closes the scanning gap in the refcountbt scanner.

v23.1: create helpers for the key extraction and comparison functions,
       improve documentation, and eliminate the ->mask_key indirect
       calls

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Dave Chinner <david@fromorbit.com>

23 files changed, 610 insertions, 129 deletions

diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
index 23f0acfc2a64..fdfa08cbf4db 100644
--- a/fs/xfs/libxfs/xfs_alloc.c
+++ b/fs/xfs/libxfs/xfs_alloc.c
@@ -3745,13 +3745,16 @@ xfs_alloc_query_all(
 	return xfs_btree_query_all(cur, xfs_alloc_query_range_helper, &query);
 }
 
-/* Is there a record covering a given extent? */
+/*
+ * Scan part of the keyspace of the free space and tell us if the area has no
+ * records, is fully mapped by records, or is partially filled.
+ */
 int
-xfs_alloc_has_record(
+xfs_alloc_has_records(
 	struct xfs_btree_cur	*cur,
 	xfs_agblock_t		bno,
 	xfs_extlen_t		len,
-	bool			*exists)
+	enum xbtree_recpacking	*outcome)
 {
 	union xfs_btree_irec	low;
 	union xfs_btree_irec	high;
@@ -3761,7 +3764,7 @@ xfs_alloc_has_record(
 	memset(&high, 0xFF, sizeof(high));
 	high.a.ar_startblock = bno + len - 1;
 
-	return xfs_btree_has_record(cur, &low, &high, exists);
+	return xfs_btree_has_records(cur, &low, &high, NULL, outcome);
 }
 
 /*
diff --git a/fs/xfs/libxfs/xfs_alloc.h b/fs/xfs/libxfs/xfs_alloc.h
index 56bd05900b35..5dbb25546d0b 100644
--- a/fs/xfs/libxfs/xfs_alloc.h
+++ b/fs/xfs/libxfs/xfs_alloc.h
@@ -213,8 +213,8 @@ int xfs_alloc_query_range(struct xfs_btree_cur *cur,
 int xfs_alloc_query_all(struct xfs_btree_cur *cur, xfs_alloc_query_range_fn fn,
 		void *priv);
 
-int xfs_alloc_has_record(struct xfs_btree_cur *cur, xfs_agblock_t bno,
-		xfs_extlen_t len, bool *exist);
+int xfs_alloc_has_records(struct xfs_btree_cur *cur, xfs_agblock_t bno,
+		xfs_extlen_t len, enum xbtree_recpacking *outcome);
 
 typedef int (*xfs_agfl_walk_fn)(struct xfs_mount *mp, xfs_agblock_t bno,
 		void *priv);
diff --git a/fs/xfs/libxfs/xfs_alloc_btree.c b/fs/xfs/libxfs/xfs_alloc_btree.c
index 8e8416c14cec..c65228efed4a 100644
--- a/fs/xfs/libxfs/xfs_alloc_btree.c
+++ b/fs/xfs/libxfs/xfs_alloc_btree.c
@@ -260,20 +260,27 @@ STATIC int64_t
 xfs_bnobt_diff_two_keys(
 	struct xfs_btree_cur		*cur,
 	const union xfs_btree_key	*k1,
-	const union xfs_btree_key	*k2)
+	const union xfs_btree_key	*k2,
+	const union xfs_btree_key	*mask)
 {
+	ASSERT(!mask || mask->alloc.ar_startblock);
+
 	return (int64_t)be32_to_cpu(k1->alloc.ar_startblock) -
-			  be32_to_cpu(k2->alloc.ar_startblock);
+			be32_to_cpu(k2->alloc.ar_startblock);
 }
 
 STATIC int64_t
 xfs_cntbt_diff_two_keys(
 	struct xfs_btree_cur		*cur,
 	const union xfs_btree_key	*k1,
-	const union xfs_btree_key	*k2)
+	const union xfs_btree_key	*k2,
+	const union xfs_btree_key	*mask)
 {
 	int64_t				diff;
 
+	ASSERT(!mask || (mask->alloc.ar_blockcount &&
+			 mask->alloc.ar_startblock));
+
 	diff =  be32_to_cpu(k1->alloc.ar_blockcount) -
 		be32_to_cpu(k2->alloc.ar_blockcount);
 	if (diff)
@@ -423,6 +430,19 @@ xfs_cntbt_recs_inorder(
 		 be32_to_cpu(r2->alloc.ar_startblock));
 }
 
+STATIC enum xbtree_key_contig
+xfs_allocbt_keys_contiguous(
+	struct xfs_btree_cur		*cur,
+	const union xfs_btree_key	*key1,
+	const union xfs_btree_key	*key2,
+	const union xfs_btree_key	*mask)
+{
+	ASSERT(!mask || mask->alloc.ar_startblock);
+
+	return xbtree_key_contig(be32_to_cpu(key1->alloc.ar_startblock),
+				 be32_to_cpu(key2->alloc.ar_startblock));
+}
+
 static const struct xfs_btree_ops xfs_bnobt_ops = {
 	.rec_len		= sizeof(xfs_alloc_rec_t),
 	.key_len		= sizeof(xfs_alloc_key_t),
@@ -443,6 +463,7 @@ static const struct xfs_btree_ops xfs_bnobt_ops = {
 	.diff_two_keys		= xfs_bnobt_diff_two_keys,
 	.keys_inorder		= xfs_bnobt_keys_inorder,
 	.recs_inorder		= xfs_bnobt_recs_inorder,
+	.keys_contiguous	= xfs_allocbt_keys_contiguous,
 };
 
 static const struct xfs_btree_ops xfs_cntbt_ops = {
@@ -465,6 +486,7 @@ static const struct xfs_btree_ops xfs_cntbt_ops = {
 	.diff_two_keys		= xfs_cntbt_diff_two_keys,
 	.keys_inorder		= xfs_cntbt_keys_inorder,
 	.recs_inorder		= xfs_cntbt_recs_inorder,
+	.keys_contiguous	= NULL, /* not needed right now */
 };
 
 /* Allocate most of a new allocation btree cursor. */
diff --git a/fs/xfs/libxfs/xfs_bmap_btree.c b/fs/xfs/libxfs/xfs_bmap_btree.c
index b8ad95050c9b..1b40e5f8b1ec 100644
--- a/fs/xfs/libxfs/xfs_bmap_btree.c
+++ b/fs/xfs/libxfs/xfs_bmap_btree.c
@@ -382,11 +382,14 @@ STATIC int64_t
 xfs_bmbt_diff_two_keys(
 	struct xfs_btree_cur		*cur,
 	const union xfs_btree_key	*k1,
-	const union xfs_btree_key	*k2)
+	const union xfs_btree_key	*k2,
+	const union xfs_btree_key	*mask)
 {
 	uint64_t			a = be64_to_cpu(k1->bmbt.br_startoff);
 	uint64_t			b = be64_to_cpu(k2->bmbt.br_startoff);
 
+	ASSERT(!mask || mask->bmbt.br_startoff);
+
 	/*
 	 * Note: This routine previously casted a and b to int64 and subtracted
 	 * them to generate a result.  This lead to problems if b was the
@@ -500,6 +503,19 @@ xfs_bmbt_recs_inorder(
 		xfs_bmbt_disk_get_startoff(&r2->bmbt);
 }
 
+STATIC enum xbtree_key_contig
+xfs_bmbt_keys_contiguous(
+	struct xfs_btree_cur		*cur,
+	const union xfs_btree_key	*key1,
+	const union xfs_btree_key	*key2,
+	const union xfs_btree_key	*mask)
+{
+	ASSERT(!mask || mask->bmbt.br_startoff);
+
+	return xbtree_key_contig(be64_to_cpu(key1->bmbt.br_startoff),
+				 be64_to_cpu(key2->bmbt.br_startoff));
+}
+
 static const struct xfs_btree_ops xfs_bmbt_ops = {
 	.rec_len		= sizeof(xfs_bmbt_rec_t),
 	.key_len		= sizeof(xfs_bmbt_key_t),
@@ -520,6 +536,7 @@ static const struct xfs_btree_ops xfs_bmbt_ops = {
 	.buf_ops		= &xfs_bmbt_buf_ops,
 	.keys_inorder		= xfs_bmbt_keys_inorder,
 	.recs_inorder		= xfs_bmbt_recs_inorder,
+	.keys_contiguous	= xfs_bmbt_keys_contiguous,
 };
 
 /*
diff --git a/fs/xfs/libxfs/xfs_btree.c b/fs/xfs/libxfs/xfs_btree.c
index c4649cc624e1..6a6503ab0cd7 100644
--- a/fs/xfs/libxfs/xfs_btree.c
+++ b/fs/xfs/libxfs/xfs_btree.c
@@ -2067,8 +2067,7 @@ xfs_btree_get_leaf_keys(
 		for (n = 2; n <= xfs_btree_get_numrecs(block); n++) {
 			rec = xfs_btree_rec_addr(cur, n, block);
 			cur->bc_ops->init_high_key_from_rec(&hkey, rec);
-			if (cur->bc_ops->diff_two_keys(cur, &hkey, &max_hkey)
-					> 0)
+			if (xfs_btree_keycmp_gt(cur, &hkey, &max_hkey))
 				max_hkey = hkey;
 		}
 
@@ -2096,7 +2095,7 @@ xfs_btree_get_node_keys(
 		max_hkey = xfs_btree_high_key_addr(cur, 1, block);
 		for (n = 2; n <= xfs_btree_get_numrecs(block); n++) {
 			hkey = xfs_btree_high_key_addr(cur, n, block);
-			if (cur->bc_ops->diff_two_keys(cur, hkey, max_hkey) > 0)
+			if (xfs_btree_keycmp_gt(cur, hkey, max_hkey))
 				max_hkey = hkey;
 		}
 
@@ -2183,8 +2182,8 @@ __xfs_btree_updkeys(
 		nlkey = xfs_btree_key_addr(cur, ptr, block);
 		nhkey = xfs_btree_high_key_addr(cur, ptr, block);
 		if (!force_all &&
-		    !(cur->bc_ops->diff_two_keys(cur, nlkey, lkey) != 0 ||
-		      cur->bc_ops->diff_two_keys(cur, nhkey, hkey) != 0))
+		    xfs_btree_keycmp_eq(cur, nlkey, lkey) &&
+		    xfs_btree_keycmp_eq(cur, nhkey, hkey))
 			break;
 		xfs_btree_copy_keys(cur, nlkey, lkey, 1);
 		xfs_btree_log_keys(cur, bp, ptr, ptr);
@@ -4716,7 +4715,6 @@ xfs_btree_simple_query_range(
 {
 	union xfs_btree_rec		*recp;
 	union xfs_btree_key		rec_key;
-	int64_t				diff;
 	int				stat;
 	bool				firstrec = true;
 	int				error;
@@ -4746,20 +4744,17 @@ xfs_btree_simple_query_range(
 		if (error || !stat)
 			break;
 
-		/* Skip if high_key(rec) < low_key. */
+		/* Skip if low_key > high_key(rec). */
 		if (firstrec) {
 			cur->bc_ops->init_high_key_from_rec(&rec_key, recp);
 			firstrec = false;
-			diff = cur->bc_ops->diff_two_keys(cur, low_key,
-					&rec_key);
-			if (diff > 0)
+			if (xfs_btree_keycmp_gt(cur, low_key, &rec_key))
 				goto advloop;
 		}
 
-		/* Stop if high_key < low_key(rec). */
+		/* Stop if low_key(rec) > high_key. */
 		cur->bc_ops->init_key_from_rec(&rec_key, recp);
-		diff = cur->bc_ops->diff_two_keys(cur, &rec_key, high_key);
-		if (diff > 0)
+		if (xfs_btree_keycmp_gt(cur, &rec_key, high_key))
 			break;
 
 		/* Callback */
@@ -4813,8 +4808,6 @@ xfs_btree_overlapped_query_range(
 	union xfs_btree_key		*hkp;
 	union xfs_btree_rec		*recp;
 	struct xfs_btree_block		*block;
-	int64_t				ldiff;
-	int64_t				hdiff;
 	int				level;
 	struct xfs_buf			*bp;
 	int				i;
@@ -4854,25 +4847,23 @@ pop_up:
 					block);
 
 			cur->bc_ops->init_high_key_from_rec(&rec_hkey, recp);
-			ldiff = cur->bc_ops->diff_two_keys(cur, &rec_hkey,
-					low_key);
-
 			cur->bc_ops->init_key_from_rec(&rec_key, recp);
-			hdiff = cur->bc_ops->diff_two_keys(cur, high_key,
-					&rec_key);
 
 			/*
+			 * If (query's high key < record's low key), then there
+			 * are no more interesting records in this block.  Pop
+			 * up to the leaf level to find more record blocks.
+			 *
 			 * If (record's high key >= query's low key) and
 			 *    (query's high key >= record's low key), then
 			 * this record overlaps the query range; callback.
 			 */
-			if (ldiff >= 0 && hdiff >= 0) {
+			if (xfs_btree_keycmp_lt(cur, high_key, &rec_key))
+				goto pop_up;
+			if (xfs_btree_keycmp_ge(cur, &rec_hkey, low_key)) {
 				error = fn(cur, recp, priv);
 				if (error)
 					break;
-			} else if (hdiff < 0) {
-				/* Record is larger than high key; pop. */
-				goto pop_up;
 			}
 			cur->bc_levels[level].ptr++;
 			continue;
@@ -4884,15 +4875,18 @@ pop_up:
 				block);
 		pp = xfs_btree_ptr_addr(cur, cur->bc_levels[level].ptr, block);
 
-		ldiff = cur->bc_ops->diff_two_keys(cur, hkp, low_key);
-		hdiff = cur->bc_ops->diff_two_keys(cur, high_key, lkp);
-
 		/*
+		 * If (query's high key < pointer's low key), then there are no
+		 * more interesting keys in this block.  Pop up one leaf level
+		 * to continue looking for records.
+		 *
 		 * If (pointer's high key >= query's low key) and
 		 *    (query's high key >= pointer's low key), then
 		 * this record overlaps the query range; follow pointer.
 		 */
-		if (ldiff >= 0 && hdiff >= 0) {
+		if (xfs_btree_keycmp_lt(cur, high_key, lkp))
+			goto pop_up;
+		if (xfs_btree_keycmp_ge(cur, hkp, low_key)) {
 			level--;
 			error = xfs_btree_lookup_get_block(cur, level, pp,
 					&block);
@@ -4907,9 +4901,6 @@ pop_up:
 #endif
 			cur->bc_levels[level].ptr = 1;
 			continue;
-		} else if (hdiff < 0) {
-			/* The low key is larger than the upper range; pop. */
-			goto pop_up;
 		}
 		cur->bc_levels[level].ptr++;
 	}
@@ -4937,6 +4928,19 @@ out:
 	return error;
 }
 
+static inline void
+xfs_btree_key_from_irec(
+	struct xfs_btree_cur		*cur,
+	union xfs_btree_key		*key,
+	const union xfs_btree_irec	*irec)
+{
+	union xfs_btree_rec		rec;
+
+	cur->bc_rec = *irec;
+	cur->bc_ops->init_rec_from_cur(cur, &rec);
+	cur->bc_ops->init_key_from_rec(key, &rec);
+}
+
 /*
  * Query a btree for all records overlapping a given interval of keys.  The
  * supplied function will be called with each record found; return one of the
@@ -4951,21 +4955,15 @@ xfs_btree_query_range(
 	xfs_btree_query_range_fn	fn,
 	void				*priv)
 {
-	union xfs_btree_rec		rec;
 	union xfs_btree_key		low_key;
 	union xfs_btree_key		high_key;
 
 	/* Find the keys of both ends of the interval. */
-	cur->bc_rec = *high_rec;
-	cur->bc_ops->init_rec_from_cur(cur, &rec);
-	cur->bc_ops->init_key_from_rec(&high_key, &rec);
+	xfs_btree_key_from_irec(cur, &high_key, high_rec);
+	xfs_btree_key_from_irec(cur, &low_key, low_rec);
 
-	cur->bc_rec = *low_rec;
-	cur->bc_ops->init_rec_from_cur(cur, &rec);
-	cur->bc_ops->init_key_from_rec(&low_key, &rec);
-
-	/* Enforce low key < high key. */
-	if (cur->bc_ops->diff_two_keys(cur, &low_key, &high_key) > 0)
+	/* Enforce low key <= high key. */
+	if (!xfs_btree_keycmp_le(cur, &low_key, &high_key))
 		return -EINVAL;
 
 	if (!(cur->bc_flags & XFS_BTREE_OVERLAPPING))
@@ -5027,34 +5025,132 @@ xfs_btree_diff_two_ptrs(
 	return (int64_t)be32_to_cpu(a->s) - be32_to_cpu(b->s);
 }
 
-/* If there's an extent, we're done. */
+struct xfs_btree_has_records {
+	/* Keys for the start and end of the range we want to know about. */
+	union xfs_btree_key		start_key;
+	union xfs_btree_key		end_key;
+
+	/* Mask for key comparisons, if desired. */
+	const union xfs_btree_key	*key_mask;
+
+	/* Highest record key we've seen so far. */
+	union xfs_btree_key		high_key;
+
+	enum xbtree_recpacking		outcome;
+};
+
 STATIC int
-xfs_btree_has_record_helper(
+xfs_btree_has_records_helper(
 	struct xfs_btree_cur		*cur,
 	const union xfs_btree_rec	*rec,
 	void				*priv)
 {
-	return -ECANCELED;
+	union xfs_btree_key		rec_key;
+	union xfs_btree_key		rec_high_key;
+	struct xfs_btree_has_records	*info = priv;
+	enum xbtree_key_contig		key_contig;
+
+	cur->bc_ops->init_key_from_rec(&rec_key, rec);
+
+	if (info->outcome == XBTREE_RECPACKING_EMPTY) {
+		info->outcome = XBTREE_RECPACKING_SPARSE;
+
+		/*
+		 * If the first record we find does not overlap the start key,
+		 * then there is a hole at the start of the search range.
+		 * Classify this as sparse and stop immediately.
+		 */
+		if (xfs_btree_masked_keycmp_lt(cur, &info->start_key, &rec_key,
+					info->key_mask))
+			return -ECANCELED;
+	} else {
+		/*
+		 * If a subsequent record does not overlap with the any record
+		 * we've seen so far, there is a hole in the middle of the
+		 * search range.  Classify this as sparse and stop.
+		 * If the keys overlap and this btree does not allow overlap,
+		 * signal corruption.
+		 */
+		key_contig = cur->bc_ops->keys_contiguous(cur, &info->high_key,
+					&rec_key, info->key_mask);
+		if (key_contig == XBTREE_KEY_OVERLAP &&
+				!(cur->bc_flags & XFS_BTREE_OVERLAPPING))
+			return -EFSCORRUPTED;
+		if (key_contig == XBTREE_KEY_GAP)
+			return -ECANCELED;
+	}
+
+	/*
+	 * If high_key(rec) is larger than any other high key we've seen,
+	 * remember it for later.
+	 */
+	cur->bc_ops->init_high_key_from_rec(&rec_high_key, rec);
+	if (xfs_btree_masked_keycmp_gt(cur, &rec_high_key, &info->high_key,
+				info->key_mask))
+		info->high_key = rec_high_key; /* struct copy */
+
+	return 0;
 }
 
-/* Is there a record covering a given range of keys? */
+/*
+ * Scan part of the keyspace of a btree and tell us if that keyspace does not
+ * map to any records; is fully mapped to records; or is partially mapped to
+ * records.  This is the btree record equivalent to determining if a file is
+ * sparse.
+ *
+ * For most btree types, the record scan should use all available btree key
+ * fields to compare the keys encountered.  These callers should pass NULL for
+ * @mask.  However, some callers (e.g.  scanning physical space in the rmapbt)
+ * want to ignore some part of the btree record keyspace when performing the
+ * comparison.  These callers should pass in a union xfs_btree_key object with
+ * the fields that *should* be a part of the comparison set to any nonzero
+ * value, and the rest zeroed.
+ */
 int
-xfs_btree_has_record(
+xfs_btree_has_records(
 	struct xfs_btree_cur		*cur,
 	const union xfs_btree_irec	*low,
 	const union xfs_btree_irec	*high,
-	bool				*exists)
+	const union xfs_btree_key	*mask,
+	enum xbtree_recpacking		*outcome)
 {
+	struct xfs_btree_has_records	info = {
+		.outcome		= XBTREE_RECPACKING_EMPTY,
+		.key_mask		= mask,
+	};
 	int				error;
 
-	error = xfs_btree_query_range(cur, low, high,
-			&xfs_btree_has_record_helper, NULL);
-	if (error == -ECANCELED) {
-		*exists = true;
-		return 0;
+	/* Not all btrees support this operation. */
+	if (!cur->bc_ops->keys_contiguous) {
+		ASSERT(0);
+		return -EOPNOTSUPP;
 	}
-	*exists = false;
-	return error;
+
+	xfs_btree_key_from_irec(cur, &info.start_key, low);
+	xfs_btree_key_from_irec(cur, &info.end_key, high);
+
+	error = xfs_btree_query_range(cur, low, high,
+			xfs_btree_has_records_helper, &info);
+	if (error == -ECANCELED)
+		goto out;
+	if (error)
+		return error;
+
+	if (info.outcome == XBTREE_RECPACKING_EMPTY)
+		goto out;
+
+	/*
+	 * If the largest high_key(rec) we saw during the walk is greater than
+	 * the end of the search range, classify this as full.  Otherwise,
+	 * there is a hole at the end of the search range.
+	 */
+	if (xfs_btree_masked_keycmp_ge(cur, &info.high_key, &info.end_key,
+				mask))
+		info.outcome = XBTREE_RECPACKING_FULL;
+
+out:
+	*outcome = info.outcome;
+	return 0;
 }
 
 /* Are there more records in this btree? */
diff --git a/fs/xfs/libxfs/xfs_btree.h b/fs/xfs/libxfs/xfs_btree.h
index 29c4b4ccb909..a2aa36b23e25 100644
--- a/fs/xfs/libxfs/xfs_btree.h
+++ b/fs/xfs/libxfs/xfs_btree.h
@@ -90,6 +90,27 @@ uint32_t xfs_btree_magic(int crc, xfs_btnum_t btnum);
 #define XFS_BTREE_STATS_ADD(cur, stat, val)	\
 	XFS_STATS_ADD_OFF((cur)->bc_mp, (cur)->bc_statoff + __XBTS_ ## stat, val)
 
+enum xbtree_key_contig {
+	XBTREE_KEY_GAP = 0,
+	XBTREE_KEY_CONTIGUOUS,
+	XBTREE_KEY_OVERLAP,
+};
+
+/*
+ * Decide if these two numeric btree key fields are contiguous, overlapping,
+ * or if there's a gap between them.  @x should be the field from the high
+ * key and @y should be the field from the low key.
+ */
+static inline enum xbtree_key_contig xbtree_key_contig(uint64_t x, uint64_t y)
+{
+	x++;
+	if (x < y)
+		return XBTREE_KEY_GAP;
+	if (x == y)
+		return XBTREE_KEY_CONTIGUOUS;
+	return XBTREE_KEY_OVERLAP;
+}
+
 struct xfs_btree_ops {
 	/* size of the key and record structures */
 	size_t	key_len;
@@ -140,11 +161,14 @@ struct xfs_btree_ops {
 
 	/*
 	 * Difference between key2 and key1 -- positive if key1 > key2,
-	 * negative if key1 < key2, and zero if equal.
+	 * negative if key1 < key2, and zero if equal.  If the @mask parameter
+	 * is non NULL, each key field to be used in the comparison must
+	 * contain a nonzero value.
 	 */
 	int64_t (*diff_two_keys)(struct xfs_btree_cur *cur,
 				 const union xfs_btree_key *key1,
-				 const union xfs_btree_key *key2);
+				 const union xfs_btree_key *key2,
+				 const union xfs_btree_key *mask);
 
 	const struct xfs_buf_ops	*buf_ops;
 
@@ -157,6 +181,22 @@ struct xfs_btree_ops {
 	int	(*recs_inorder)(struct xfs_btree_cur *cur,
 				const union xfs_btree_rec *r1,
 				const union xfs_btree_rec *r2);
+
+	/*
+	 * Are these two btree keys immediately adjacent?
+	 *
+	 * Given two btree keys @key1 and @key2, decide if it is impossible for
+	 * there to be a third btree key K satisfying the relationship
+	 * @key1 < K < @key2.  To determine if two btree records are
+	 * immediately adjacent, @key1 should be the high key of the first
+	 * record and @key2 should be the low key of the second record.
+	 * If the @mask parameter is non NULL, each key field to be used in the
+	 * comparison must contain a nonzero value.
+	 */
+	enum xbtree_key_contig (*keys_contiguous)(struct xfs_btree_cur *cur,
+			       const union xfs_btree_key *key1,
+			       const union xfs_btree_key *key2,
+			       const union xfs_btree_key *mask);
 };
 
 /*
@@ -540,12 +580,105 @@ void xfs_btree_get_keys(struct xfs_btree_cur *cur,
 		struct xfs_btree_block *block, union xfs_btree_key *key);
 union xfs_btree_key *xfs_btree_high_key_from_key(struct xfs_btree_cur *cur,
 		union xfs_btree_key *key);
-int xfs_btree_has_record(struct xfs_btree_cur *cur,
+typedef bool (*xfs_btree_key_gap_fn)(struct xfs_btree_cur *cur,
+		const union xfs_btree_key *key1,
+		const union xfs_btree_key *key2);
+
+int xfs_btree_has_records(struct xfs_btree_cur *cur,
 		const union xfs_btree_irec *low,
-		const union xfs_btree_irec *high, bool *exists);
+		const union xfs_btree_irec *high,
+		const union xfs_btree_key *mask,
+		enum xbtree_recpacking *outcome);
+
 bool xfs_btree_has_more_records(struct xfs_btree_cur *cur);
 struct xfs_ifork *xfs_btree_ifork_ptr(struct xfs_btree_cur *cur);
 
+/* Key comparison helpers */
+static inline bool
+xfs_btree_keycmp_lt(
+	struct xfs_btree_cur		*cur,
+	const union xfs_btree_key	*key1,
+	const union xfs_btree_key	*key2)
+{
+	return cur->bc_ops->diff_two_keys(cur, key1, key2, NULL) < 0;
+}
+
+static inline bool
+xfs_btree_keycmp_gt(
+	struct xfs_btree_cur		*cur,
+	const union xfs_btree_key	*key1,
+	const union xfs_btree_key	*key2)
+{
+	return cur->bc_ops->diff_two_keys(cur, key1, key2, NULL) > 0;
+}
+
+static inline bool
+xfs_btree_keycmp_eq(
+	struct xfs_btree_cur		*cur,
+	const union xfs_btree_key	*key1,
+	const union xfs_btree_key	*key2)
+{
+	return cur->bc_ops->diff_two_keys(cur, key1, key2, NULL) == 0;
+}
+
+static inline bool
+xfs_btree_keycmp_le(
+	struct xfs_btree_cur		*cur,
+	const union xfs_btree_key	*key1,
+	const union xfs_btree_key	*key2)
+{
+	return !xfs_btree_keycmp_gt(cur, key1, key2);
+}
+
+static inline bool
+xfs_btree_keycmp_ge(
+	struct xfs_btree_cur		*cur,
+	const union xfs_btree_key	*key1,
+	const union xfs_btree_key	*key2)
+{
+	return !xfs_btree_keycmp_lt(cur, key1, key2);
+}
+
+static inline bool
+xfs_btree_keycmp_ne(
+	struct xfs_btree_cur		*cur,
+	const union xfs_btree_key	*key1,
+	const union xfs_btree_key	*key2)
+{
+	return !xfs_btree_keycmp_eq(cur, key1, key2);
+}
+
+/* Masked key comparison helpers */
+static inline bool
+xfs_btree_masked_keycmp_lt(
+	struct xfs_btree_cur		*cur,
+	const union xfs_btree_key	*key1,
+	const union xfs_btree_key	*key2,
+	const union xfs_btree_key	*mask)
+{
+	return cur->bc_ops->diff_two_keys(cur, key1, key2, mask) < 0;
+}
+
+static inline bool
+xfs_btree_masked_keycmp_gt(
+	struct xfs_btree_cur		*cur,
+	const union xfs_btree_key	*key1,
+	const union xfs_btree_key	*key2,
+	const union xfs_btree_key	*mask)
+{
+	return cur->bc_ops->diff_two_keys(cur, key1, key2, mask) > 0;
+}
+
+static inline bool
+xfs_btree_masked_keycmp_ge(
+	struct xfs_btree_cur		*cur,
+	const union xfs_btree_key	*key1,
+	const union xfs_btree_key	*key2,
+	const union xfs_btree_key	*mask)
+{
+	return !xfs_btree_masked_keycmp_lt(cur, key1, key2, mask);
+}
+
 /* Does this cursor point to the last block in the given level? */
 static inline bool
 xfs_btree_islastblock(
diff --git a/fs/xfs/libxfs/xfs_ialloc_btree.c b/fs/xfs/libxfs/xfs_ialloc_btree.c
index f900c056b82c..5a945ae21b5d 100644
--- a/fs/xfs/libxfs/xfs_ialloc_btree.c
+++ b/fs/xfs/libxfs/xfs_ialloc_btree.c
@@ -269,10 +269,13 @@ STATIC int64_t
 xfs_inobt_diff_two_keys(
 	struct xfs_btree_cur		*cur,
 	const union xfs_btree_key	*k1,
-	const union xfs_btree_key	*k2)
+	const union xfs_btree_key	*k2,
+	const union xfs_btree_key	*mask)
 {
+	ASSERT(!mask || mask->inobt.ir_startino);
+
 	return (int64_t)be32_to_cpu(k1->inobt.ir_startino) -
-			  be32_to_cpu(k2->inobt.ir_startino);
+			be32_to_cpu(k2->inobt.ir_startino);
 }
 
 static xfs_failaddr_t
@@ -383,6 +386,19 @@ xfs_inobt_recs_inorder(
 		be32_to_cpu(r2->inobt.ir_startino);
 }
 
+STATIC enum xbtree_key_contig
+xfs_inobt_keys_contiguous(
+	struct xfs_btree_cur		*cur,
+	const union xfs_btree_key	*key1,
+	const union xfs_btree_key	*key2,
+	const union xfs_btree_key	*mask)
+{
+	ASSERT(!mask || mask->inobt.ir_startino);
+
+	return xbtree_key_contig(be32_to_cpu(key1->inobt.ir_startino),
+				 be32_to_cpu(key2->inobt.ir_startino));
+}
+
 static const struct xfs_btree_ops xfs_inobt_ops = {
 	.rec_len		= sizeof(xfs_inobt_rec_t),
 	.key_len		= sizeof(xfs_inobt_key_t),
@@ -402,6 +418,7 @@ static const struct xfs_btree_ops xfs_inobt_ops = {
 	.diff_two_keys		= xfs_inobt_diff_two_keys,
 	.keys_inorder		= xfs_inobt_keys_inorder,
 	.recs_inorder		= xfs_inobt_recs_inorder,
+	.keys_contiguous	= xfs_inobt_keys_contiguous,
 };
 
 static const struct xfs_btree_ops xfs_finobt_ops = {
@@ -423,6 +440,7 @@ static const struct xfs_btree_ops xfs_finobt_ops = {
 	.diff_two_keys		= xfs_inobt_diff_two_keys,
 	.keys_inorder		= xfs_inobt_keys_inorder,
 	.recs_inorder		= xfs_inobt_recs_inorder,
+	.keys_contiguous	= xfs_inobt_keys_contiguous,
 };
 
 /*
diff --git a/fs/xfs/libxfs/xfs_refcount.c b/fs/xfs/libxfs/xfs_refcount.c
index 335f84bef81c..c1c65774dcc2 100644
--- a/fs/xfs/libxfs/xfs_refcount.c
+++ b/fs/xfs/libxfs/xfs_refcount.c
@@ -1998,14 +1998,17 @@ out_free:
 	return error;
 }
 
-/* Is there a record covering a given extent? */
+/*
+ * Scan part of the keyspace of the refcount records and tell us if the area
+ * has no records, is fully mapped by records, or is partially filled.
+ */
 int
-xfs_refcount_has_record(
+xfs_refcount_has_records(
 	struct xfs_btree_cur	*cur,
 	enum xfs_refc_domain	domain,
 	xfs_agblock_t		bno,
 	xfs_extlen_t		len,
-	bool			*exists)
+	enum xbtree_recpacking	*outcome)
 {
 	union xfs_btree_irec	low;
 	union xfs_btree_irec	high;
@@ -2016,7 +2019,7 @@ xfs_refcount_has_record(
 	high.rc.rc_startblock = bno + len - 1;
 	low.rc.rc_domain = high.rc.rc_domain = domain;
 
-	return xfs_btree_has_record(cur, &low, &high, exists);
+	return xfs_btree_has_records(cur, &low, &high, NULL, outcome);
 }
 
 int __init
diff --git a/fs/xfs/libxfs/xfs_refcount.h b/fs/xfs/libxfs/xfs_refcount.h
index fc0b58d4c379..783cd89ca195 100644
--- a/fs/xfs/libxfs/xfs_refcount.h
+++ b/fs/xfs/libxfs/xfs_refcount.h
@@ -111,9 +111,9 @@ extern int xfs_refcount_recover_cow_leftovers(struct xfs_mount *mp,
  */
 #define XFS_REFCOUNT_ITEM_OVERHEAD	32
 
-extern int xfs_refcount_has_record(struct xfs_btree_cur *cur,
+extern int xfs_refcount_has_records(struct xfs_btree_cur *cur,
 		enum xfs_refc_domain domain, xfs_agblock_t bno,
-		xfs_extlen_t len, bool *exists);
+		xfs_extlen_t len, enum xbtree_recpacking *outcome);
 union xfs_btree_rec;
 extern void xfs_refcount_btrec_to_irec(const union xfs_btree_rec *rec,
 		struct xfs_refcount_irec *irec);
diff --git a/fs/xfs/libxfs/xfs_refcount_btree.c b/fs/xfs/libxfs/xfs_refcount_btree.c
index 03d2b01487a1..d4afc5f4e6a5 100644
--- a/fs/xfs/libxfs/xfs_refcount_btree.c
+++ b/fs/xfs/libxfs/xfs_refcount_btree.c
@@ -202,10 +202,13 @@ STATIC int64_t
 xfs_refcountbt_diff_two_keys(
 	struct xfs_btree_cur		*cur,
 	const union xfs_btree_key	*k1,
-	const union xfs_btree_key	*k2)
+	const union xfs_btree_key	*k2,
+	const union xfs_btree_key	*mask)
 {
+	ASSERT(!mask || mask->refc.rc_startblock);
+
 	return (int64_t)be32_to_cpu(k1->refc.rc_startblock) -
-			  be32_to_cpu(k2->refc.rc_startblock);
+			be32_to_cpu(k2->refc.rc_startblock);
 }
 
 STATIC xfs_failaddr_t
@@ -300,6 +303,19 @@ xfs_refcountbt_recs_inorder(
 		be32_to_cpu(r2->refc.rc_startblock);
 }
 
+STATIC enum xbtree_key_contig
+xfs_refcountbt_keys_contiguous(
+	struct xfs_btree_cur		*cur,
+	const union xfs_btree_key	*key1,
+	const union xfs_btree_key	*key2,
+	const union xfs_btree_key	*mask)
+{
+	ASSERT(!mask || mask->refc.rc_startblock);
+
+	return xbtree_key_contig(be32_to_cpu(key1->refc.rc_startblock),
+				 be32_to_cpu(key2->refc.rc_startblock));
+}
+
 static const struct xfs_btree_ops xfs_refcountbt_ops = {
 	.rec_len		= sizeof(struct xfs_refcount_rec),
 	.key_len		= sizeof(struct xfs_refcount_key),
@@ -319,6 +335,7 @@ static const struct xfs_btree_ops xfs_refcountbt_ops = {
 	.diff_two_keys		= xfs_refcountbt_diff_two_keys,
 	.keys_inorder		= xfs_refcountbt_keys_inorder,
 	.recs_inorder		= xfs_refcountbt_recs_inorder,
+	.keys_contiguous	= xfs_refcountbt_keys_contiguous,
 };
 
 /*
diff --git a/fs/xfs/libxfs/xfs_rmap.c b/fs/xfs/libxfs/xfs_rmap.c
index da008d317f83..308b81f321eb 100644
--- a/fs/xfs/libxfs/xfs_rmap.c
+++ b/fs/xfs/libxfs/xfs_rmap.c
@@ -2709,14 +2709,21 @@ xfs_rmap_compare(
 		return 0;
 }
 
-/* Is there a record covering a given extent? */
+/*
+ * Scan the physical storage part of the keyspace of the reverse mapping index
+ * and tell us if the area has no records, is fully mapped by records, or is
+ * partially filled.
+ */
 int
-xfs_rmap_has_record(
+xfs_rmap_has_records(
 	struct xfs_btree_cur	*cur,
 	xfs_agblock_t		bno,
 	xfs_extlen_t		len,
-	bool			*exists)
+	enum xbtree_recpacking	*outcome)
 {
+	union xfs_btree_key	mask = {
+		.rmap.rm_startblock = cpu_to_be32(-1U),
+	};
 	union xfs_btree_irec	low;
 	union xfs_btree_irec	high;
 
@@ -2725,7 +2732,7 @@ xfs_rmap_has_record(
 	memset(&high, 0xFF, sizeof(high));
 	high.r.rm_startblock = bno + len - 1;
 
-	return xfs_btree_has_record(cur, &low, &high, exists);
+	return xfs_btree_has_records(cur, &low, &high, &mask, outcome);
 }
 
 /*
diff --git a/fs/xfs/libxfs/xfs_rmap.h b/fs/xfs/libxfs/xfs_rmap.h
index 7fb298bcc15f..4cbe50cf522e 100644
--- a/fs/xfs/libxfs/xfs_rmap.h
+++ b/fs/xfs/libxfs/xfs_rmap.h
@@ -198,8 +198,8 @@ xfs_failaddr_t xfs_rmap_btrec_to_irec(const union xfs_btree_rec *rec,
 xfs_failaddr_t xfs_rmap_check_irec(struct xfs_btree_cur *cur,
 		const struct xfs_rmap_irec *irec);
 
-int xfs_rmap_has_record(struct xfs_btree_cur *cur, xfs_agblock_t bno,
-		xfs_extlen_t len, bool *exists);
+int xfs_rmap_has_records(struct xfs_btree_cur *cur, xfs_agblock_t bno,
+		xfs_extlen_t len, enum xbtree_recpacking *outcome);
 int xfs_rmap_record_exists(struct xfs_btree_cur *cur, xfs_agblock_t bno,
 		xfs_extlen_t len, const struct xfs_owner_info *oinfo,
 		bool *has_rmap);
diff --git a/fs/xfs/libxfs/xfs_rmap_btree.c b/fs/xfs/libxfs/xfs_rmap_btree.c
index 84e2b692f034..6c81b20e97d2 100644
--- a/fs/xfs/libxfs/xfs_rmap_btree.c
+++ b/fs/xfs/libxfs/xfs_rmap_btree.c
@@ -273,31 +273,43 @@ STATIC int64_t
 xfs_rmapbt_diff_two_keys(
 	struct xfs_btree_cur		*cur,
 	const union xfs_btree_key	*k1,
-	const union xfs_btree_key	*k2)
+	const union xfs_btree_key	*k2,
+	const union xfs_btree_key	*mask)
 {
 	const struct xfs_rmap_key	*kp1 = &k1->rmap;
 	const struct xfs_rmap_key	*kp2 = &k2->rmap;
 	int64_t				d;
 	__u64				x, y;
 
+	/* Doesn't make sense to mask off the physical space part */
+	ASSERT(!mask || mask->rmap.rm_startblock);
+
 	d = (int64_t)be32_to_cpu(kp1->rm_startblock) -
-		       be32_to_cpu(kp2->rm_startblock);
+		     be32_to_cpu(kp2->rm_startblock);
 	if (d)
 		return d;
 
-	x = be64_to_cpu(kp1->rm_owner);
-	y = be64_to_cpu(kp2->rm_owner);
-	if (x > y)
-		return 1;
-	else if (y > x)
-		return -1;
+	if (!mask || mask->rmap.rm_owner) {
+		x = be64_to_cpu(kp1->rm_owner);
+		y = be64_to_cpu(kp2->rm_owner);
+		if (x > y)
+			return 1;
+		else if (y > x)
+			return -1;
+	}
+
+	if (!mask || mask->rmap.rm_offset) {
+		/* Doesn't make sense to allow offset but not owner */
+		ASSERT(!mask || mask->rmap.rm_owner);
+
+		x = offset_keymask(be64_to_cpu(kp1->rm_offset));
+		y = offset_keymask(be64_to_cpu(kp2->rm_offset));
+		if (x > y)
+			return 1;
+		else if (y > x)
+			return -1;
+	}
 
-	x = offset_keymask(be64_to_cpu(kp1->rm_offset));
-	y = offset_keymask(be64_to_cpu(kp2->rm_offset));
-	if (x > y)
-		return 1;
-	else if (y > x)
-		return -1;
 	return 0;
 }
 
@@ -444,6 +456,26 @@ xfs_rmapbt_recs_inorder(
 	return 0;
 }
 
+STATIC enum xbtree_key_contig
+xfs_rmapbt_keys_contiguous(
+	struct xfs_btree_cur		*cur,
+	const union xfs_btree_key	*key1,
+	const union xfs_btree_key	*key2,
+	const union xfs_btree_key	*mask)
+{
+	ASSERT(!mask || mask->rmap.rm_startblock);
+
+	/*
+	 * We only support checking contiguity of the physical space component.
+	 * If any callers ever need more specificity than that, they'll have to
+	 * implement it here.
+	 */
+	ASSERT(!mask || (!mask->rmap.rm_owner && !mask->rmap.rm_offset));
+
+	return xbtree_key_contig(be32_to_cpu(key1->rmap.rm_startblock),
+				 be32_to_cpu(key2->rmap.rm_startblock));
+}
+
 static const struct xfs_btree_ops xfs_rmapbt_ops = {
 	.rec_len		= sizeof(struct xfs_rmap_rec),
 	.key_len		= 2 * sizeof(struct xfs_rmap_key),
@@ -463,6 +495,7 @@ static const struct xfs_btree_ops xfs_rmapbt_ops = {
 	.diff_two_keys		= xfs_rmapbt_diff_two_keys,
 	.keys_inorder		= xfs_rmapbt_keys_inorder,
 	.recs_inorder		= xfs_rmapbt_recs_inorder,
+	.keys_contiguous	= xfs_rmapbt_keys_contiguous,
 };
 
 static struct xfs_btree_cur *
diff --git a/fs/xfs/libxfs/xfs_types.h b/fs/xfs/libxfs/xfs_types.h
index 5ebdda7e1078..851220021484 100644
--- a/fs/xfs/libxfs/xfs_types.h
+++ b/fs/xfs/libxfs/xfs_types.h
@@ -204,6 +204,18 @@ enum xfs_ag_resv_type {
 	XFS_AG_RESV_RMAPBT,
 };
 
+/* Results of scanning a btree keyspace to check occupancy. */
+enum xbtree_recpacking {
+	/* None of the keyspace maps to records. */
+	XBTREE_RECPACKING_EMPTY = 0,
+
+	/* Some, but not all, of the keyspace maps to records. */
+	XBTREE_RECPACKING_SPARSE,
+
+	/* The entire keyspace maps to records. */
+	XBTREE_RECPACKING_FULL,
+};
+
 /*
  * Type verifier functions
  */
diff --git a/fs/xfs/scrub/agheader.c b/fs/xfs/scrub/agheader.c
index 87cb13a6e84a..1a84153afa91 100644
--- a/fs/xfs/scrub/agheader.c
+++ b/fs/xfs/scrub/agheader.c
@@ -53,6 +53,7 @@ xchk_superblock_xref(
 	xchk_xref_is_not_inode_chunk(sc, agbno, 1);
 	xchk_xref_is_owned_by(sc, agbno, 1, &XFS_RMAP_OINFO_FS);
 	xchk_xref_is_not_shared(sc, agbno, 1);
+	xchk_xref_is_not_cow_staging(sc, agbno, 1);
 
 	/* scrub teardown will take care of sc->sa for us */
 }
@@ -517,6 +518,7 @@ xchk_agf_xref(
 	xchk_xref_is_owned_by(sc, agbno, 1, &XFS_RMAP_OINFO_FS);
 	xchk_agf_xref_btreeblks(sc);
 	xchk_xref_is_not_shared(sc, agbno, 1);
+	xchk_xref_is_not_cow_staging(sc, agbno, 1);
 	xchk_agf_xref_refcblks(sc);
 
 	/* scrub teardown will take care of sc->sa for us */
@@ -644,6 +646,7 @@ xchk_agfl_block_xref(
 	xchk_xref_is_not_inode_chunk(sc, agbno, 1);
 	xchk_xref_is_owned_by(sc, agbno, 1, &XFS_RMAP_OINFO_AG);
 	xchk_xref_is_not_shared(sc, agbno, 1);
+	xchk_xref_is_not_cow_staging(sc, agbno, 1);
 }
 
 /* Scrub an AGFL block. */
@@ -700,6 +703,7 @@ xchk_agfl_xref(
 	xchk_xref_is_not_inode_chunk(sc, agbno, 1);
 	xchk_xref_is_owned_by(sc, agbno, 1, &XFS_RMAP_OINFO_FS);
 	xchk_xref_is_not_shared(sc, agbno, 1);
+	xchk_xref_is_not_cow_staging(sc, agbno, 1);
 
 	/*
 	 * Scrub teardown will take care of sc->sa for us.  Leave sc->sa
@@ -855,6 +859,7 @@ xchk_agi_xref(
 	xchk_agi_xref_icounts(sc);
 	xchk_xref_is_owned_by(sc, agbno, 1, &XFS_RMAP_OINFO_FS);
 	xchk_xref_is_not_shared(sc, agbno, 1);
+	xchk_xref_is_not_cow_staging(sc, agbno, 1);
 	xchk_agi_xref_fiblocks(sc);
 
 	/* scrub teardown will take care of sc->sa for us */
diff --git a/fs/xfs/scrub/alloc.c b/fs/xfs/scrub/alloc.c
index 53de04c6027c..12dd55ac2a4f 100644
--- a/fs/xfs/scrub/alloc.c
+++ b/fs/xfs/scrub/alloc.c
@@ -90,6 +90,7 @@ xchk_allocbt_xref(
 	xchk_xref_is_not_inode_chunk(sc, agbno, len);
 	xchk_xref_has_no_owner(sc, agbno, len);
 	xchk_xref_is_not_shared(sc, agbno, len);
+	xchk_xref_is_not_cow_staging(sc, agbno, len);
 }
 
 /* Scrub a bnobt/cntbt record. */
@@ -144,15 +145,15 @@ xchk_xref_is_used_space(
 	xfs_agblock_t		agbno,
 	xfs_extlen_t		len)
 {
-	bool			is_freesp;
+	enum xbtree_recpacking	outcome;
 	int			error;
 
 	if (!sc->sa.bno_cur || xchk_skip_xref(sc->sm))
 		return;
 
-	error = xfs_alloc_has_record(sc->sa.bno_cur, agbno, len, &is_freesp);
+	error = xfs_alloc_has_records(sc->sa.bno_cur, agbno, len, &outcome);
 	if (!xchk_should_check_xref(sc, &error, &sc->sa.bno_cur))
 		return;
-	if (is_freesp)
+	if (outcome != XBTREE_RECPACKING_EMPTY)
 		xchk_btree_xref_set_corrupt(sc, sc->sa.bno_cur, 0);
 }
diff --git a/fs/xfs/scrub/bmap.c b/fs/xfs/scrub/bmap.c
index 6188eba672e5..be2c4da2808b 100644
--- a/fs/xfs/scrub/bmap.c
+++ b/fs/xfs/scrub/bmap.c
@@ -328,12 +328,17 @@ xchk_bmap_iextent_xref(
 	xchk_bmap_xref_rmap(info, irec, agbno);
 	switch (info->whichfork) {
 	case XFS_DATA_FORK:
-		if (xfs_is_reflink_inode(info->sc->ip))
-			break;
-		fallthrough;
+		if (!xfs_is_reflink_inode(info->sc->ip))
+			xchk_xref_is_not_shared(info->sc, agbno,
+					irec->br_blockcount);
+		xchk_xref_is_not_cow_staging(info->sc, agbno,
+				irec->br_blockcount);
+		break;
 	case XFS_ATTR_FORK:
 		xchk_xref_is_not_shared(info->sc, agbno,
 				irec->br_blockcount);
+		xchk_xref_is_not_cow_staging(info->sc, agbno,
+				irec->br_blockcount);
 		break;
 	case XFS_COW_FORK:
 		xchk_xref_is_cow_staging(info->sc, agbno,
diff --git a/fs/xfs/scrub/btree.c b/fs/xfs/scrub/btree.c
index 4ec3b1cab018..1165dc05a179 100644
--- a/fs/xfs/scrub/btree.c
+++ b/fs/xfs/scrub/btree.c
@@ -161,20 +161,20 @@ xchk_btree_rec(
 	if (cur->bc_nlevels == 1)
 		return;
 
-	/* Is this at least as large as the parent low key? */
+	/* Is low_key(rec) at least as large as the parent low key? */
 	cur->bc_ops->init_key_from_rec(&key, rec);
 	keyblock = xfs_btree_get_block(cur, 1, &bp);
 	keyp = xfs_btree_key_addr(cur, cur->bc_levels[1].ptr, keyblock);
-	if (cur->bc_ops->diff_two_keys(cur, &key, keyp) < 0)
+	if (xfs_btree_keycmp_lt(cur, &key, keyp))
 		xchk_btree_set_corrupt(bs->sc, cur, 1);
 
 	if (!(cur->bc_flags & XFS_BTREE_OVERLAPPING))
 		return;
 
-	/* Is this no larger than the parent high key? */
+	/* Is high_key(rec) no larger than the parent high key? */
 	cur->bc_ops->init_high_key_from_rec(&hkey, rec);
 	keyp = xfs_btree_high_key_addr(cur, cur->bc_levels[1].ptr, keyblock);
-	if (cur->bc_ops->diff_two_keys(cur, keyp, &hkey) < 0)
+	if (xfs_btree_keycmp_lt(cur, keyp, &hkey))
 		xchk_btree_set_corrupt(bs->sc, cur, 1);
 }
 
@@ -209,20 +209,20 @@ xchk_btree_key(
 	if (level + 1 >= cur->bc_nlevels)
 		return;
 
-	/* Is this at least as large as the parent low key? */
+	/* Is this block's low key at least as large as the parent low key? */
 	keyblock = xfs_btree_get_block(cur, level + 1, &bp);
 	keyp = xfs_btree_key_addr(cur, cur->bc_levels[level + 1].ptr, keyblock);
-	if (cur->bc_ops->diff_two_keys(cur, key, keyp) < 0)
+	if (xfs_btree_keycmp_lt(cur, key, keyp))
 		xchk_btree_set_corrupt(bs->sc, cur, level);
 
 	if (!(cur->bc_flags & XFS_BTREE_OVERLAPPING))
 		return;
 
-	/* Is this no larger than the parent high key? */
+	/* Is this block's high key no larger than the parent high key? */
 	key = xfs_btree_high_key_addr(cur, cur->bc_levels[level].ptr, block);
 	keyp = xfs_btree_high_key_addr(cur, cur->bc_levels[level + 1].ptr,
 			keyblock);
-	if (cur->bc_ops->diff_two_keys(cur, keyp, key) < 0)
+	if (xfs_btree_keycmp_lt(cur, keyp, key))
 		xchk_btree_set_corrupt(bs->sc, cur, level);
 }
 
@@ -557,7 +557,7 @@ xchk_btree_block_check_keys(
 	parent_block = xfs_btree_get_block(cur, level + 1, &bp);
 	parent_low_key = xfs_btree_key_addr(cur, cur->bc_levels[level + 1].ptr,
 			parent_block);
-	if (cur->bc_ops->diff_two_keys(cur, &block_key, parent_low_key)) {
+	if (xfs_btree_keycmp_ne(cur, &block_key, parent_low_key)) {
 		xchk_btree_set_corrupt(bs->sc, bs->cur, level);
 		return;
 	}
@@ -569,7 +569,7 @@ xchk_btree_block_check_keys(
 	parent_high_key = xfs_btree_high_key_addr(cur,
 			cur->bc_levels[level + 1].ptr, parent_block);
 	block_high_key = xfs_btree_high_key_from_key(cur, &block_key);
-	if (cur->bc_ops->diff_two_keys(cur, block_high_key, parent_high_key))
+	if (xfs_btree_keycmp_ne(cur, block_high_key, parent_high_key))
 		xchk_btree_set_corrupt(bs->sc, bs->cur, level);
 }
 
@@ -661,7 +661,7 @@ xchk_btree_block_keys(
 	parent_keys = xfs_btree_key_addr(cur, cur->bc_levels[level + 1].ptr,
 			parent_block);
 
-	if (cur->bc_ops->diff_two_keys(cur, &block_keys, parent_keys) != 0)
+	if (xfs_btree_keycmp_ne(cur, &block_keys, parent_keys))
 		xchk_btree_set_corrupt(bs->sc, cur, 1);
 
 	if (!(cur->bc_flags & XFS_BTREE_OVERLAPPING))
@@ -672,7 +672,7 @@ xchk_btree_block_keys(
 	high_pk = xfs_btree_high_key_addr(cur, cur->bc_levels[level + 1].ptr,
 			parent_block);
 
-	if (cur->bc_ops->diff_two_keys(cur, high_bk, high_pk) != 0)
+	if (xfs_btree_keycmp_ne(cur, high_bk, high_pk))
 		xchk_btree_set_corrupt(bs->sc, cur, 1);
 }
 
diff --git a/fs/xfs/scrub/ialloc.c b/fs/xfs/scrub/ialloc.c
index ca5a7e0f5451..6d08613db32f 100644
--- a/fs/xfs/scrub/ialloc.c
+++ b/fs/xfs/scrub/ialloc.c
@@ -115,7 +115,7 @@ xchk_iallocbt_chunk(
 		xchk_btree_set_corrupt(bs->sc, bs->cur, 0);
 
 	xchk_iallocbt_chunk_xref(bs->sc, irec, agino, bno, len);
-
+	xchk_xref_is_not_cow_staging(bs->sc, bno, len);
 	return true;
 }
 
diff --git a/fs/xfs/scrub/inode.c b/fs/xfs/scrub/inode.c
index bbf9432c02c2..50ebd72f6d95 100644
--- a/fs/xfs/scrub/inode.c
+++ b/fs/xfs/scrub/inode.c
@@ -558,6 +558,7 @@ xchk_inode_xref(
 	xchk_inode_xref_finobt(sc, ino);
 	xchk_xref_is_owned_by(sc, agbno, 1, &XFS_RMAP_OINFO_INODES);
 	xchk_xref_is_not_shared(sc, agbno, 1);
+	xchk_xref_is_not_cow_staging(sc, agbno, 1);
 	xchk_inode_xref_bmap(sc, dip);
 
 out_free:
diff --git a/fs/xfs/scrub/refcount.c b/fs/xfs/scrub/refcount.c
index 4d77049dfce2..db9e46a4f8d4 100644
--- a/fs/xfs/scrub/refcount.c
+++ b/fs/xfs/scrub/refcount.c
@@ -332,6 +332,64 @@ xchk_refcountbt_xref(
 	xchk_refcountbt_xref_rmap(sc, irec);
 }
 
+struct xchk_refcbt_records {
+	/* The next AG block where we aren't expecting shared extents. */
+	xfs_agblock_t		next_unshared_agbno;
+
+	/* Number of CoW blocks we expect. */
+	xfs_agblock_t		cow_blocks;
+
+	/* Was the last record a shared or CoW staging extent? */
+	enum xfs_refc_domain	prev_domain;
+};
+
+STATIC int
+xchk_refcountbt_rmap_check_gap(
+	struct xfs_btree_cur		*cur,
+	const struct xfs_rmap_irec	*rec,
+	void				*priv)
+{
+	xfs_agblock_t			*next_bno = priv;
+
+	if (*next_bno != NULLAGBLOCK && rec->rm_startblock < *next_bno)
+		return -ECANCELED;
+
+	*next_bno = rec->rm_startblock + rec->rm_blockcount;
+	return 0;
+}
+
+/*
+ * Make sure that a gap in the reference count records does not correspond to
+ * overlapping records (i.e. shared extents) in the reverse mappings.
+ */
+static inline void
+xchk_refcountbt_xref_gaps(
+	struct xfs_scrub	*sc,
+	struct xchk_refcbt_records *rrc,
+	xfs_agblock_t		bno)
+{
+	struct xfs_rmap_irec	low;
+	struct xfs_rmap_irec	high;
+	xfs_agblock_t		next_bno = NULLAGBLOCK;
+	int			error;
+
+	if (bno <= rrc->next_unshared_agbno || !sc->sa.rmap_cur ||
+            xchk_skip_xref(sc->sm))
+		return;
+
+	memset(&low, 0, sizeof(low));
+	low.rm_startblock = rrc->next_unshared_agbno;
+	memset(&high, 0xFF, sizeof(high));
+	high.rm_startblock = bno - 1;
+
+	error = xfs_rmap_query_range(sc->sa.rmap_cur, &low, &high,
+			xchk_refcountbt_rmap_check_gap, &next_bno);
+	if (error == -ECANCELED)
+		xchk_btree_xref_set_corrupt(sc, sc->sa.rmap_cur, 0);
+	else
+		xchk_should_check_xref(sc, &error, &sc->sa.rmap_cur);
+}
+
 /* Scrub a refcountbt record. */
 STATIC int
 xchk_refcountbt_rec(
@@ -339,7 +397,7 @@ xchk_refcountbt_rec(
 	const union xfs_btree_rec *rec)
 {
 	struct xfs_refcount_irec irec;
-	xfs_agblock_t		*cow_blocks = bs->private;
+	struct xchk_refcbt_records *rrc = bs->private;
 
 	xfs_refcount_btrec_to_irec(rec, &irec);
 	if (xfs_refcount_check_irec(bs->cur, &irec) != NULL) {
@@ -348,10 +406,27 @@ xchk_refcountbt_rec(
 	}
 
 	if (irec.rc_domain == XFS_REFC_DOMAIN_COW)
-		(*cow_blocks) += irec.rc_blockcount;
+		rrc->cow_blocks += irec.rc_blockcount;
+
+	/* Shared records always come before CoW records. */
+	if (irec.rc_domain == XFS_REFC_DOMAIN_SHARED &&
+	    rrc->prev_domain == XFS_REFC_DOMAIN_COW)
+		xchk_btree_set_corrupt(bs->sc, bs->cur, 0);
+	rrc->prev_domain = irec.rc_domain;
 
 	xchk_refcountbt_xref(bs->sc, &irec);
 
+	/*
+	 * If this is a record for a shared extent, check that all blocks
+	 * between the previous record and this one have at most one reverse
+	 * mapping.
+	 */
+	if (irec.rc_domain == XFS_REFC_DOMAIN_SHARED) {
+		xchk_refcountbt_xref_gaps(bs->sc, rrc, irec.rc_startblock);
+		rrc->next_unshared_agbno = irec.rc_startblock +
+					   irec.rc_blockcount;
+	}
+
 	return 0;
 }
 
@@ -393,15 +468,25 @@ int
 xchk_refcountbt(
 	struct xfs_scrub	*sc)
 {
-	xfs_agblock_t		cow_blocks = 0;
+	struct xchk_refcbt_records rrc = {
+		.cow_blocks		= 0,
+		.next_unshared_agbno	= 0,
+		.prev_domain		= XFS_REFC_DOMAIN_SHARED,
+	};
 	int			error;
 
 	error = xchk_btree(sc, sc->sa.refc_cur, xchk_refcountbt_rec,
-			&XFS_RMAP_OINFO_REFC, &cow_blocks);
+			&XFS_RMAP_OINFO_REFC, &rrc);
 	if (error)
 		return error;
 
-	xchk_refcount_xref_rmap(sc, cow_blocks);
+	/*
+	 * Check that all blocks between the last refcount > 1 record and the
+	 * end of the AG have at most one reverse mapping.
+	 */
+	xchk_refcountbt_xref_gaps(sc, &rrc, sc->mp->m_sb.sb_agblocks);
+
+	xchk_refcount_xref_rmap(sc, rrc.cow_blocks);
 
 	return 0;
 }
@@ -457,16 +542,37 @@ xchk_xref_is_not_shared(
 	xfs_agblock_t		agbno,
 	xfs_extlen_t		len)
 {
-	bool			shared;
+	enum xbtree_recpacking	outcome;
+	int			error;
+
+	if (!sc->sa.refc_cur || xchk_skip_xref(sc->sm))
+		return;
+
+	error = xfs_refcount_has_records(sc->sa.refc_cur,
+			XFS_REFC_DOMAIN_SHARED, agbno, len, &outcome);
+	if (!xchk_should_check_xref(sc, &error, &sc->sa.refc_cur))
+		return;
+	if (outcome != XBTREE_RECPACKING_EMPTY)
+		xchk_btree_xref_set_corrupt(sc, sc->sa.refc_cur, 0);
+}
+
+/* xref check that the extent is not being used for CoW staging. */
+void
+xchk_xref_is_not_cow_staging(
+	struct xfs_scrub	*sc,
+	xfs_agblock_t		agbno,
+	xfs_extlen_t		len)
+{
+	enum xbtree_recpacking	outcome;
 	int			error;
 
 	if (!sc->sa.refc_cur || xchk_skip_xref(sc->sm))
 		return;
 
-	error = xfs_refcount_has_record(sc->sa.refc_cur, XFS_REFC_DOMAIN_SHARED,
-			agbno, len, &shared);
+	error = xfs_refcount_has_records(sc->sa.refc_cur, XFS_REFC_DOMAIN_COW,
+			agbno, len, &outcome);
 	if (!xchk_should_check_xref(sc, &error, &sc->sa.refc_cur))
 		return;
-	if (shared)
+	if (outcome != XBTREE_RECPACKING_EMPTY)
 		xchk_btree_xref_set_corrupt(sc, sc->sa.refc_cur, 0);
 }
diff --git a/fs/xfs/scrub/rmap.c b/fs/xfs/scrub/rmap.c
index 8e78e1bc9eef..2f9e4f77db6b 100644
--- a/fs/xfs/scrub/rmap.c
+++ b/fs/xfs/scrub/rmap.c
@@ -219,15 +219,15 @@ xchk_xref_has_no_owner(
 	xfs_agblock_t		bno,
 	xfs_extlen_t		len)
 {
-	bool			has_rmap;
+	enum xbtree_recpacking	outcome;
 	int			error;
 
 	if (!sc->sa.rmap_cur || xchk_skip_xref(sc->sm))
 		return;
 
-	error = xfs_rmap_has_record(sc->sa.rmap_cur, bno, len, &has_rmap);
+	error = xfs_rmap_has_records(sc->sa.rmap_cur, bno, len, &outcome);
 	if (!xchk_should_check_xref(sc, &error, &sc->sa.rmap_cur))
 		return;
-	if (has_rmap)
+	if (outcome != XBTREE_RECPACKING_EMPTY)
 		xchk_btree_xref_set_corrupt(sc, sc->sa.rmap_cur, 0);
 }
diff --git a/fs/xfs/scrub/scrub.h b/fs/xfs/scrub/scrub.h
index d85c3b883b4c..b6f452eb9645 100644
--- a/fs/xfs/scrub/scrub.h
+++ b/fs/xfs/scrub/scrub.h
@@ -172,6 +172,8 @@ void xchk_xref_is_cow_staging(struct xfs_scrub *sc, xfs_agblock_t bno,
 		xfs_extlen_t len);
 void xchk_xref_is_not_shared(struct xfs_scrub *sc, xfs_agblock_t bno,
 		xfs_extlen_t len);
+void xchk_xref_is_not_cow_staging(struct xfs_scrub *sc, xfs_agblock_t bno,
+		xfs_extlen_t len);
 #ifdef CONFIG_XFS_RT
 void xchk_xref_is_used_rt_space(struct xfs_scrub *sc, xfs_rtblock_t rtbno,
 		xfs_extlen_t len);