diff mbox series

[28/43] xfs: scrub the realtime refcount btree

Message ID 173405125046.1182620.123195236500556349.stgit@frogsfrogsfrogs (mailing list archive)
State New
Headers show
Series [01/43] xfs: prepare refcount btree cursor tracepoints for realtime | expand

Commit Message

Darrick J. Wong Dec. 13, 2024, 1:17 a.m. UTC
From: Darrick J. Wong <djwong@kernel.org>

Add code to scrub realtime refcount btrees.

Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
---
 fs/xfs/Makefile           |    1 
 fs/xfs/libxfs/xfs_fs.h    |    3 
 fs/xfs/scrub/common.c     |   10 +
 fs/xfs/scrub/common.h     |    5 
 fs/xfs/scrub/health.c     |    1 
 fs/xfs/scrub/rtrefcount.c |  487 +++++++++++++++++++++++++++++++++++++++++++++
 fs/xfs/scrub/scrub.c      |    7 +
 fs/xfs/scrub/scrub.h      |    3 
 fs/xfs/scrub/stats.c      |    1 
 fs/xfs/scrub/trace.h      |    4 
 10 files changed, 519 insertions(+), 3 deletions(-)
 create mode 100644 fs/xfs/scrub/rtrefcount.c

Comments

Christoph Hellwig Dec. 13, 2024, 9:18 a.m. UTC | #1
On Thu, Dec 12, 2024 at 05:17:32PM -0800, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@kernel.org>
> 
> Add code to scrub realtime refcount btrees.

Please explain what that actually means here.
Darrick J. Wong Dec. 17, 2024, 8:55 p.m. UTC | #2
On Fri, Dec 13, 2024 at 01:18:06AM -0800, Christoph Hellwig wrote:
> On Thu, Dec 12, 2024 at 05:17:32PM -0800, Darrick J. Wong wrote:
> > From: Darrick J. Wong <djwong@kernel.org>
> > 
> > Add code to scrub realtime refcount btrees.
> 
> Please explain what that actually means here.

How about:

"Add code to scrub realtime refcount btrees.  Similar to the refcount
btree checking code for the data device, we walk the rmap btree for
each refcount record to confirm that the reference counts are correct."

--D
Christoph Hellwig Dec. 18, 2024, 6:55 a.m. UTC | #3
On Tue, Dec 17, 2024 at 12:55:10PM -0800, Darrick J. Wong wrote:
> "Add code to scrub realtime refcount btrees.  Similar to the refcount
> btree checking code for the data device, we walk the rmap btree for
> each refcount record to confirm that the reference counts are correct."

Sounds good.
diff mbox series

Patch

diff --git a/fs/xfs/Makefile b/fs/xfs/Makefile
index b9356d01416e16..9dd9921e53567c 100644
--- a/fs/xfs/Makefile
+++ b/fs/xfs/Makefile
@@ -195,6 +195,7 @@  xfs-$(CONFIG_XFS_ONLINE_SCRUB_STATS) += scrub/stats.o
 xfs-$(CONFIG_XFS_RT)		+= $(addprefix scrub/, \
 				   rgsuper.o \
 				   rtbitmap.o \
+				   rtrefcount.o \
 				   rtrmap.o \
 				   rtsummary.o \
 				   )
diff --git a/fs/xfs/libxfs/xfs_fs.h b/fs/xfs/libxfs/xfs_fs.h
index ea9e58a89d92d3..a4bd6a39c6ba71 100644
--- a/fs/xfs/libxfs/xfs_fs.h
+++ b/fs/xfs/libxfs/xfs_fs.h
@@ -738,9 +738,10 @@  struct xfs_scrub_metadata {
 #define XFS_SCRUB_TYPE_METAPATH	29	/* metadata directory tree paths */
 #define XFS_SCRUB_TYPE_RGSUPER	30	/* realtime superblock */
 #define XFS_SCRUB_TYPE_RTRMAPBT	31	/* rtgroup reverse mapping btree */
+#define XFS_SCRUB_TYPE_RTREFCBT	32	/* realtime reference count btree */
 
 /* Number of scrub subcommands. */
-#define XFS_SCRUB_TYPE_NR	32
+#define XFS_SCRUB_TYPE_NR	33
 
 /*
  * This special type code only applies to the vectored scrub implementation.
diff --git a/fs/xfs/scrub/common.c b/fs/xfs/scrub/common.c
index ab2509ef3bc10c..43e75ab717d8a1 100644
--- a/fs/xfs/scrub/common.c
+++ b/fs/xfs/scrub/common.c
@@ -37,6 +37,7 @@ 
 #include "xfs_rtgroup.h"
 #include "xfs_rtrmap_btree.h"
 #include "xfs_bmap_util.h"
+#include "xfs_rtrefcount_btree.h"
 #include "scrub/scrub.h"
 #include "scrub/common.h"
 #include "scrub/trace.h"
@@ -797,6 +798,9 @@  xchk_rtgroup_lock(
 	if (xfs_has_rtrmapbt(sc->mp) && (rtglock_flags & XFS_RTGLOCK_RMAP))
 		sr->rmap_cur = xfs_rtrmapbt_init_cursor(sc->tp, sr->rtg);
 
+	if (xfs_has_rtreflink(sc->mp) && (rtglock_flags & XFS_RTGLOCK_REFCOUNT))
+		sr->refc_cur = xfs_rtrefcountbt_init_cursor(sc->tp, sr->rtg);
+
 	return 0;
 }
 
@@ -811,7 +815,10 @@  xchk_rtgroup_btcur_free(
 {
 	if (sr->rmap_cur)
 		xfs_btree_del_cursor(sr->rmap_cur, XFS_BTREE_ERROR);
+	if (sr->refc_cur)
+		xfs_btree_del_cursor(sr->refc_cur, XFS_BTREE_ERROR);
 
+	sr->refc_cur = NULL;
 	sr->rmap_cur = NULL;
 }
 
@@ -1690,6 +1697,9 @@  xchk_meta_btree_count_blocks(
 	case XFS_METAFILE_RTRMAP:
 		cur = xfs_rtrmapbt_init_cursor(sc->tp, sc->sr.rtg);
 		break;
+	case XFS_METAFILE_RTREFCOUNT:
+		cur = xfs_rtrefcountbt_init_cursor(sc->tp, sc->sr.rtg);
+		break;
 	default:
 		ASSERT(0);
 		return -EFSCORRUPTED;
diff --git a/fs/xfs/scrub/common.h b/fs/xfs/scrub/common.h
index 50ac6cca18fe45..bdcd40f0ec742c 100644
--- a/fs/xfs/scrub/common.h
+++ b/fs/xfs/scrub/common.h
@@ -82,11 +82,13 @@  int xchk_setup_rtbitmap(struct xfs_scrub *sc);
 int xchk_setup_rtsummary(struct xfs_scrub *sc);
 int xchk_setup_rgsuperblock(struct xfs_scrub *sc);
 int xchk_setup_rtrmapbt(struct xfs_scrub *sc);
+int xchk_setup_rtrefcountbt(struct xfs_scrub *sc);
 #else
 # define xchk_setup_rtbitmap		xchk_setup_nothing
 # define xchk_setup_rtsummary		xchk_setup_nothing
 # define xchk_setup_rgsuperblock	xchk_setup_nothing
 # define xchk_setup_rtrmapbt		xchk_setup_nothing
+# define xchk_setup_rtrefcountbt	xchk_setup_nothing
 #endif
 #ifdef CONFIG_XFS_QUOTA
 int xchk_ino_dqattach(struct xfs_scrub *sc);
@@ -129,7 +131,8 @@  xchk_ag_init_existing(
 
 /* All the locks we need to check an rtgroup. */
 #define XCHK_RTGLOCK_ALL	(XFS_RTGLOCK_BITMAP | \
-				 XFS_RTGLOCK_RMAP)
+				 XFS_RTGLOCK_RMAP | \
+				 XFS_RTGLOCK_REFCOUNT)
 
 int xchk_rtgroup_init(struct xfs_scrub *sc, xfs_rgnumber_t rgno,
 		struct xchk_rt *sr);
diff --git a/fs/xfs/scrub/health.c b/fs/xfs/scrub/health.c
index bcc4244e3b55db..3c0f25098b69f0 100644
--- a/fs/xfs/scrub/health.c
+++ b/fs/xfs/scrub/health.c
@@ -115,6 +115,7 @@  static const struct xchk_health_map type_to_health_flag[XFS_SCRUB_TYPE_NR] = {
 	[XFS_SCRUB_TYPE_METAPATH]	= { XHG_FS,  XFS_SICK_FS_METAPATH },
 	[XFS_SCRUB_TYPE_RGSUPER]	= { XHG_RTGROUP, XFS_SICK_RG_SUPER },
 	[XFS_SCRUB_TYPE_RTRMAPBT]	= { XHG_RTGROUP, XFS_SICK_RG_RMAPBT },
+	[XFS_SCRUB_TYPE_RTREFCBT]	= { XHG_RTGROUP, XFS_SICK_RG_REFCNTBT },
 };
 
 /* Return the health status mask for this scrub type. */
diff --git a/fs/xfs/scrub/rtrefcount.c b/fs/xfs/scrub/rtrefcount.c
new file mode 100644
index 00000000000000..92ae2e15ae9f79
--- /dev/null
+++ b/fs/xfs/scrub/rtrefcount.c
@@ -0,0 +1,487 @@ 
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2021-2024 Oracle.  All Rights Reserved.
+ * Author: Darrick J. Wong <djwong@kernel.org>
+ */
+#include "xfs.h"
+#include "xfs_fs.h"
+#include "xfs_shared.h"
+#include "xfs_format.h"
+#include "xfs_trans_resv.h"
+#include "xfs_mount.h"
+#include "xfs_btree.h"
+#include "xfs_rmap.h"
+#include "xfs_refcount.h"
+#include "xfs_inode.h"
+#include "xfs_rtbitmap.h"
+#include "xfs_rtgroup.h"
+#include "xfs_metafile.h"
+#include "xfs_rtrefcount_btree.h"
+#include "scrub/scrub.h"
+#include "scrub/common.h"
+#include "scrub/btree.h"
+
+/* Set us up with the realtime refcount metadata locked. */
+int
+xchk_setup_rtrefcountbt(
+	struct xfs_scrub	*sc)
+{
+	int			error;
+
+	if (xchk_need_intent_drain(sc))
+		xchk_fsgates_enable(sc, XCHK_FSGATES_DRAIN);
+
+	error = xchk_rtgroup_init(sc, sc->sm->sm_agno, &sc->sr);
+	if (error)
+		return error;
+
+	error = xchk_setup_rt(sc);
+	if (error)
+		return error;
+
+	error = xchk_install_live_inode(sc, rtg_refcount(sc->sr.rtg));
+	if (error)
+		return error;
+
+	return xchk_rtgroup_lock(sc, &sc->sr, XCHK_RTGLOCK_ALL);
+}
+
+/* Realtime Reference count btree scrubber. */
+
+/*
+ * Confirming Reference Counts via Reverse Mappings
+ *
+ * We want to count the reverse mappings overlapping a refcount record
+ * (bno, len, refcount), allowing for the possibility that some of the
+ * overlap may come from smaller adjoining reverse mappings, while some
+ * comes from single extents which overlap the range entirely.  The
+ * outer loop is as follows:
+ *
+ * 1. For all reverse mappings overlapping the refcount extent,
+ *    a. If a given rmap completely overlaps, mark it as seen.
+ *    b. Otherwise, record the fragment (in agbno order) for later
+ *       processing.
+ *
+ * Once we've seen all the rmaps, we know that for all blocks in the
+ * refcount record we want to find $refcount owners and we've already
+ * visited $seen extents that overlap all the blocks.  Therefore, we
+ * need to find ($refcount - $seen) owners for every block in the
+ * extent; call that quantity $target_nr.  Proceed as follows:
+ *
+ * 2. Pull the first $target_nr fragments from the list; all of them
+ *    should start at or before the start of the extent.
+ *    Call this subset of fragments the working set.
+ * 3. Until there are no more unprocessed fragments,
+ *    a. Find the shortest fragments in the set and remove them.
+ *    b. Note the block number of the end of these fragments.
+ *    c. Pull the same number of fragments from the list.  All of these
+ *       fragments should start at the block number recorded in the
+ *       previous step.
+ *    d. Put those fragments in the set.
+ * 4. Check that there are $target_nr fragments remaining in the list,
+ *    and that they all end at or beyond the end of the refcount extent.
+ *
+ * If the refcount is correct, all the check conditions in the algorithm
+ * should always hold true.  If not, the refcount is incorrect.
+ */
+struct xchk_rtrefcnt_frag {
+	struct list_head	list;
+	struct xfs_rmap_irec	rm;
+};
+
+struct xchk_rtrefcnt_check {
+	struct xfs_scrub	*sc;
+	struct list_head	fragments;
+
+	/* refcount extent we're examining */
+	xfs_rgblock_t		bno;
+	xfs_extlen_t		len;
+	xfs_nlink_t		refcount;
+
+	/* number of owners seen */
+	xfs_nlink_t		seen;
+};
+
+/*
+ * Decide if the given rmap is large enough that we can redeem it
+ * towards refcount verification now, or if it's a fragment, in
+ * which case we'll hang onto it in the hopes that we'll later
+ * discover that we've collected exactly the correct number of
+ * fragments as the rtrefcountbt says we should have.
+ */
+STATIC int
+xchk_rtrefcountbt_rmap_check(
+	struct xfs_btree_cur		*cur,
+	const struct xfs_rmap_irec	*rec,
+	void				*priv)
+{
+	struct xchk_rtrefcnt_check	*refchk = priv;
+	struct xchk_rtrefcnt_frag	*frag;
+	xfs_rgblock_t			rm_last;
+	xfs_rgblock_t			rc_last;
+	int				error = 0;
+
+	if (xchk_should_terminate(refchk->sc, &error))
+		return error;
+
+	rm_last = rec->rm_startblock + rec->rm_blockcount - 1;
+	rc_last = refchk->bno + refchk->len - 1;
+
+	/* Confirm that a single-owner refc extent is a CoW stage. */
+	if (refchk->refcount == 1 && rec->rm_owner != XFS_RMAP_OWN_COW) {
+		xchk_btree_xref_set_corrupt(refchk->sc, cur, 0);
+		return 0;
+	}
+
+	if (rec->rm_startblock <= refchk->bno && rm_last >= rc_last) {
+		/*
+		 * The rmap overlaps the refcount record, so we can confirm
+		 * one refcount owner seen.
+		 */
+		refchk->seen++;
+	} else {
+		/*
+		 * This rmap covers only part of the refcount record, so
+		 * save the fragment for later processing.  If the rmapbt
+		 * is healthy each rmap_irec we see will be in agbno order
+		 * so we don't need insertion sort here.
+		 */
+		frag = kmalloc(sizeof(struct xchk_rtrefcnt_frag),
+				XCHK_GFP_FLAGS);
+		if (!frag)
+			return -ENOMEM;
+		memcpy(&frag->rm, rec, sizeof(frag->rm));
+		list_add_tail(&frag->list, &refchk->fragments);
+	}
+
+	return 0;
+}
+
+/*
+ * Given a bunch of rmap fragments, iterate through them, keeping
+ * a running tally of the refcount.  If this ever deviates from
+ * what we expect (which is the rtrefcountbt's refcount minus the
+ * number of extents that totally covered the rtrefcountbt extent),
+ * we have a rtrefcountbt error.
+ */
+STATIC void
+xchk_rtrefcountbt_process_rmap_fragments(
+	struct xchk_rtrefcnt_check	*refchk)
+{
+	struct list_head		worklist;
+	struct xchk_rtrefcnt_frag	*frag;
+	struct xchk_rtrefcnt_frag	*n;
+	xfs_rgblock_t			bno;
+	xfs_rgblock_t			rbno;
+	xfs_rgblock_t			next_rbno;
+	xfs_nlink_t			nr;
+	xfs_nlink_t			target_nr;
+
+	target_nr = refchk->refcount - refchk->seen;
+	if (target_nr == 0)
+		return;
+
+	/*
+	 * There are (refchk->rc.rc_refcount - refchk->nr refcount)
+	 * references we haven't found yet.  Pull that many off the
+	 * fragment list and figure out where the smallest rmap ends
+	 * (and therefore the next rmap should start).  All the rmaps
+	 * we pull off should start at or before the beginning of the
+	 * refcount record's range.
+	 */
+	INIT_LIST_HEAD(&worklist);
+	rbno = NULLRGBLOCK;
+
+	/* Make sure the fragments actually /are/ in bno order. */
+	bno = 0;
+	list_for_each_entry(frag, &refchk->fragments, list) {
+		if (frag->rm.rm_startblock < bno)
+			goto done;
+		bno = frag->rm.rm_startblock;
+	}
+
+	/*
+	 * Find all the rmaps that start at or before the refc extent,
+	 * and put them on the worklist.
+	 */
+	nr = 0;
+	list_for_each_entry_safe(frag, n, &refchk->fragments, list) {
+		if (frag->rm.rm_startblock > refchk->bno || nr > target_nr)
+			break;
+		bno = frag->rm.rm_startblock + frag->rm.rm_blockcount;
+		if (bno < rbno)
+			rbno = bno;
+		list_move_tail(&frag->list, &worklist);
+		nr++;
+	}
+
+	/*
+	 * We should have found exactly $target_nr rmap fragments starting
+	 * at or before the refcount extent.
+	 */
+	if (nr != target_nr)
+		goto done;
+
+	while (!list_empty(&refchk->fragments)) {
+		/* Discard any fragments ending at rbno from the worklist. */
+		nr = 0;
+		next_rbno = NULLRGBLOCK;
+		list_for_each_entry_safe(frag, n, &worklist, list) {
+			bno = frag->rm.rm_startblock + frag->rm.rm_blockcount;
+			if (bno != rbno) {
+				if (bno < next_rbno)
+					next_rbno = bno;
+				continue;
+			}
+			list_del(&frag->list);
+			kfree(frag);
+			nr++;
+		}
+
+		/* Try to add nr rmaps starting at rbno to the worklist. */
+		list_for_each_entry_safe(frag, n, &refchk->fragments, list) {
+			bno = frag->rm.rm_startblock + frag->rm.rm_blockcount;
+			if (frag->rm.rm_startblock != rbno)
+				goto done;
+			list_move_tail(&frag->list, &worklist);
+			if (next_rbno > bno)
+				next_rbno = bno;
+			nr--;
+			if (nr == 0)
+				break;
+		}
+
+		/*
+		 * If we get here and nr > 0, this means that we added fewer
+		 * items to the worklist than we discarded because the fragment
+		 * list ran out of items.  Therefore, we cannot maintain the
+		 * required refcount.  Something is wrong, so we're done.
+		 */
+		if (nr)
+			goto done;
+
+		rbno = next_rbno;
+	}
+
+	/*
+	 * Make sure the last extent we processed ends at or beyond
+	 * the end of the refcount extent.
+	 */
+	if (rbno < refchk->bno + refchk->len)
+		goto done;
+
+	/* Actually record us having seen the remaining refcount. */
+	refchk->seen = refchk->refcount;
+done:
+	/* Delete fragments and work list. */
+	list_for_each_entry_safe(frag, n, &worklist, list) {
+		list_del(&frag->list);
+		kfree(frag);
+	}
+	list_for_each_entry_safe(frag, n, &refchk->fragments, list) {
+		list_del(&frag->list);
+		kfree(frag);
+	}
+}
+
+/* Use the rmap entries covering this extent to verify the refcount. */
+STATIC void
+xchk_rtrefcountbt_xref_rmap(
+	struct xfs_scrub		*sc,
+	const struct xfs_refcount_irec	*irec)
+{
+	struct xchk_rtrefcnt_check	refchk = {
+		.sc			= sc,
+		.bno			= irec->rc_startblock,
+		.len			= irec->rc_blockcount,
+		.refcount		= irec->rc_refcount,
+		.seen			= 0,
+	};
+	struct xfs_rmap_irec		low;
+	struct xfs_rmap_irec		high;
+	struct xchk_rtrefcnt_frag	*frag;
+	struct xchk_rtrefcnt_frag	*n;
+	int				error;
+
+	if (!sc->sr.rmap_cur || xchk_skip_xref(sc->sm))
+		return;
+
+	/* Cross-reference with the rmapbt to confirm the refcount. */
+	memset(&low, 0, sizeof(low));
+	low.rm_startblock = irec->rc_startblock;
+	memset(&high, 0xFF, sizeof(high));
+	high.rm_startblock = irec->rc_startblock + irec->rc_blockcount - 1;
+
+	INIT_LIST_HEAD(&refchk.fragments);
+	error = xfs_rmap_query_range(sc->sr.rmap_cur, &low, &high,
+			xchk_rtrefcountbt_rmap_check, &refchk);
+	if (!xchk_should_check_xref(sc, &error, &sc->sr.rmap_cur))
+		goto out_free;
+
+	xchk_rtrefcountbt_process_rmap_fragments(&refchk);
+	if (irec->rc_refcount != refchk.seen)
+		xchk_btree_xref_set_corrupt(sc, sc->sr.rmap_cur, 0);
+
+out_free:
+	list_for_each_entry_safe(frag, n, &refchk.fragments, list) {
+		list_del(&frag->list);
+		kfree(frag);
+	}
+}
+
+/* Cross-reference with the other btrees. */
+STATIC void
+xchk_rtrefcountbt_xref(
+	struct xfs_scrub		*sc,
+	const struct xfs_refcount_irec	*irec)
+{
+	if (sc->sm->sm_flags & XFS_SCRUB_OFLAG_CORRUPT)
+		return;
+
+	xchk_xref_is_used_rt_space(sc,
+			xfs_rgbno_to_rtb(sc->sr.rtg, irec->rc_startblock),
+			irec->rc_blockcount);
+	xchk_rtrefcountbt_xref_rmap(sc, irec);
+}
+
+struct xchk_rtrefcbt_records {
+	/* Previous refcount record. */
+	struct xfs_refcount_irec	prev_rec;
+
+	/* Number of CoW blocks we expect. */
+	xfs_extlen_t			cow_blocks;
+};
+
+static inline bool
+xchk_rtrefcount_mergeable(
+	struct xchk_rtrefcbt_records	*rrc,
+	const struct xfs_refcount_irec	*r2)
+{
+	const struct xfs_refcount_irec	*r1 = &rrc->prev_rec;
+
+	/* Ignore if prev_rec is not yet initialized. */
+	if (r1->rc_blockcount > 0)
+		return false;
+
+	if (r1->rc_startblock + r1->rc_blockcount != r2->rc_startblock)
+		return false;
+	if (r1->rc_refcount != r2->rc_refcount)
+		return false;
+	if ((unsigned long long)r1->rc_blockcount + r2->rc_blockcount >
+			XFS_REFC_LEN_MAX)
+		return false;
+
+	return true;
+}
+
+/* Flag failures for records that could be merged. */
+STATIC void
+xchk_rtrefcountbt_check_mergeable(
+	struct xchk_btree		*bs,
+	struct xchk_rtrefcbt_records	*rrc,
+	const struct xfs_refcount_irec	*irec)
+{
+	if (bs->sc->sm->sm_flags & XFS_SCRUB_OFLAG_CORRUPT)
+		return;
+
+	if (xchk_rtrefcount_mergeable(rrc, irec))
+		xchk_btree_set_corrupt(bs->sc, bs->cur, 0);
+
+	memcpy(&rrc->prev_rec, irec, sizeof(struct xfs_refcount_irec));
+}
+
+/* Scrub a rtrefcountbt record. */
+STATIC int
+xchk_rtrefcountbt_rec(
+	struct xchk_btree		*bs,
+	const union xfs_btree_rec	*rec)
+{
+	struct xfs_mount		*mp = bs->cur->bc_mp;
+	struct xchk_rtrefcbt_records	*rrc = bs->private;
+	struct xfs_refcount_irec	irec;
+	u32				mod;
+
+	xfs_refcount_btrec_to_irec(rec, &irec);
+	if (xfs_rtrefcount_check_irec(to_rtg(bs->cur->bc_group), &irec) !=
+			NULL) {
+		xchk_btree_set_corrupt(bs->sc, bs->cur, 0);
+		return 0;
+	}
+
+	/* We can only share full rt extents. */
+	mod = xfs_rgbno_to_rtxoff(mp, irec.rc_startblock);
+	if (mod)
+		xchk_btree_set_corrupt(bs->sc, bs->cur, 0);
+	mod = xfs_extlen_to_rtxmod(mp, irec.rc_blockcount);
+	if (mod)
+		xchk_btree_set_corrupt(bs->sc, bs->cur, 0);
+
+	if (irec.rc_domain == XFS_REFC_DOMAIN_COW)
+		rrc->cow_blocks += irec.rc_blockcount;
+
+	xchk_rtrefcountbt_check_mergeable(bs, rrc, &irec);
+	xchk_rtrefcountbt_xref(bs->sc, &irec);
+
+	return 0;
+}
+
+/* Make sure we have as many refc blocks as the rmap says. */
+STATIC void
+xchk_refcount_xref_rmap(
+	struct xfs_scrub	*sc,
+	const struct xfs_owner_info *btree_oinfo,
+	xfs_extlen_t		cow_blocks)
+{
+	xfs_filblks_t		refcbt_blocks = 0;
+	xfs_filblks_t		blocks;
+	int			error;
+
+	if (!sc->sr.rmap_cur || !sc->sa.rmap_cur || xchk_skip_xref(sc->sm))
+		return;
+
+	/* Check that we saw as many refcbt blocks as the rmap knows about. */
+	error = xfs_btree_count_blocks(sc->sr.refc_cur, &refcbt_blocks);
+	if (!xchk_btree_process_error(sc, sc->sr.refc_cur, 0, &error))
+		return;
+	error = xchk_count_rmap_ownedby_ag(sc, sc->sa.rmap_cur, btree_oinfo,
+			&blocks);
+	if (!xchk_should_check_xref(sc, &error, &sc->sa.rmap_cur))
+		return;
+	if (blocks != refcbt_blocks)
+		xchk_btree_xref_set_corrupt(sc, sc->sa.rmap_cur, 0);
+
+	/* Check that we saw as many cow blocks as the rmap knows about. */
+	error = xchk_count_rmap_ownedby_ag(sc, sc->sr.rmap_cur,
+			&XFS_RMAP_OINFO_COW, &blocks);
+	if (!xchk_should_check_xref(sc, &error, &sc->sr.rmap_cur))
+		return;
+	if (blocks != cow_blocks)
+		xchk_btree_xref_set_corrupt(sc, sc->sr.rmap_cur, 0);
+}
+
+/* Scrub the refcount btree for some AG. */
+int
+xchk_rtrefcountbt(
+	struct xfs_scrub	*sc)
+{
+	struct xfs_owner_info	btree_oinfo;
+	struct xchk_rtrefcbt_records rrc = {
+		.cow_blocks	= 0,
+	};
+	int			error;
+
+	error = xchk_metadata_inode_forks(sc);
+	if (error || (sc->sm->sm_flags & XFS_SCRUB_OFLAG_CORRUPT))
+		return error;
+
+	xfs_rmap_ino_bmbt_owner(&btree_oinfo, rtg_refcount(sc->sr.rtg)->i_ino,
+			XFS_DATA_FORK);
+	error = xchk_btree(sc, sc->sr.refc_cur, xchk_rtrefcountbt_rec,
+			&btree_oinfo, &rrc);
+	if (error || (sc->sm->sm_flags & XFS_SCRUB_OFLAG_CORRUPT))
+		return error;
+
+	xchk_refcount_xref_rmap(sc, &btree_oinfo, rrc.cow_blocks);
+
+	return 0;
+}
diff --git a/fs/xfs/scrub/scrub.c b/fs/xfs/scrub/scrub.c
index 16da054b2eb0dc..6e31f12cef4cc9 100644
--- a/fs/xfs/scrub/scrub.c
+++ b/fs/xfs/scrub/scrub.c
@@ -467,6 +467,13 @@  static const struct xchk_meta_ops meta_scrub_ops[] = {
 		.has	= xfs_has_rtrmapbt,
 		.repair	= xrep_rtrmapbt,
 	},
+	[XFS_SCRUB_TYPE_RTREFCBT] = {	/* realtime refcountbt */
+		.type	= ST_RTGROUP,
+		.setup	= xchk_setup_rtrefcountbt,
+		.scrub	= xchk_rtrefcountbt,
+		.has	= xfs_has_rtreflink,
+		.repair	= xrep_notsupported,
+	},
 };
 
 static int
diff --git a/fs/xfs/scrub/scrub.h b/fs/xfs/scrub/scrub.h
index cba4e89a3a627b..ab3d221dd9ed2d 100644
--- a/fs/xfs/scrub/scrub.h
+++ b/fs/xfs/scrub/scrub.h
@@ -129,6 +129,7 @@  struct xchk_rt {
 
 	/* rtgroup btrees */
 	struct xfs_btree_cur	*rmap_cur;
+	struct xfs_btree_cur	*refc_cur;
 };
 
 struct xfs_scrub {
@@ -284,11 +285,13 @@  int xchk_rtbitmap(struct xfs_scrub *sc);
 int xchk_rtsummary(struct xfs_scrub *sc);
 int xchk_rgsuperblock(struct xfs_scrub *sc);
 int xchk_rtrmapbt(struct xfs_scrub *sc);
+int xchk_rtrefcountbt(struct xfs_scrub *sc);
 #else
 # define xchk_rtbitmap		xchk_nothing
 # define xchk_rtsummary		xchk_nothing
 # define xchk_rgsuperblock	xchk_nothing
 # define xchk_rtrmapbt		xchk_nothing
+# define xchk_rtrefcountbt	xchk_nothing
 #endif
 #ifdef CONFIG_XFS_QUOTA
 int xchk_quota(struct xfs_scrub *sc);
diff --git a/fs/xfs/scrub/stats.c b/fs/xfs/scrub/stats.c
index eb6bb170c902b3..f8a37ea9779192 100644
--- a/fs/xfs/scrub/stats.c
+++ b/fs/xfs/scrub/stats.c
@@ -83,6 +83,7 @@  static const char *name_map[XFS_SCRUB_TYPE_NR] = {
 	[XFS_SCRUB_TYPE_METAPATH]	= "metapath",
 	[XFS_SCRUB_TYPE_RGSUPER]	= "rgsuper",
 	[XFS_SCRUB_TYPE_RTRMAPBT]	= "rtrmapbt",
+	[XFS_SCRUB_TYPE_RTREFCBT]	= "rtrefcountbt",
 };
 
 /* Format the scrub stats into a text buffer, similar to pcp style. */
diff --git a/fs/xfs/scrub/trace.h b/fs/xfs/scrub/trace.h
index fb86b746bc174a..289e39d1f418ba 100644
--- a/fs/xfs/scrub/trace.h
+++ b/fs/xfs/scrub/trace.h
@@ -77,6 +77,7 @@  TRACE_DEFINE_ENUM(XFS_SCRUB_TYPE_BARRIER);
 TRACE_DEFINE_ENUM(XFS_SCRUB_TYPE_METAPATH);
 TRACE_DEFINE_ENUM(XFS_SCRUB_TYPE_RGSUPER);
 TRACE_DEFINE_ENUM(XFS_SCRUB_TYPE_RTRMAPBT);
+TRACE_DEFINE_ENUM(XFS_SCRUB_TYPE_RTREFCBT);
 
 #define XFS_SCRUB_TYPE_STRINGS \
 	{ XFS_SCRUB_TYPE_PROBE,		"probe" }, \
@@ -111,7 +112,8 @@  TRACE_DEFINE_ENUM(XFS_SCRUB_TYPE_RTRMAPBT);
 	{ XFS_SCRUB_TYPE_BARRIER,	"barrier" }, \
 	{ XFS_SCRUB_TYPE_METAPATH,	"metapath" }, \
 	{ XFS_SCRUB_TYPE_RGSUPER,	"rgsuper" }, \
-	{ XFS_SCRUB_TYPE_RTRMAPBT,	"rtrmapbt" }
+	{ XFS_SCRUB_TYPE_RTRMAPBT,	"rtrmapbt" }, \
+	{ XFS_SCRUB_TYPE_RTREFCBT,	"rtrefcountbt" }
 
 #define XFS_SCRUB_FLAG_STRINGS \
 	{ XFS_SCRUB_IFLAG_REPAIR,		"repair" }, \