xfs: online repair of the realtime refcount btree

Port the data device's refcount btree repair code to the realtime
refcount btree.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>

7 files changed, 787 insertions, 7 deletions

diff --git a/fs/xfs/scrub/bmap_repair.c b/fs/xfs/scrub/bmap_repair.c
index d3ed1c884353..2256b77e20fc 100644
--- a/fs/xfs/scrub/bmap_repair.c
+++ b/fs/xfs/scrub/bmap_repair.c
@@ -285,7 +285,7 @@ xrep_bmap_check_rtfork_rmap(
 
 	/* Make sure this isn't free space. */
 	return xrep_require_rtext_inuse(sc, rec->rm_startblock,
-			rec->rm_blockcount);
+			rec->rm_blockcount, false);
 }
 
 /* Record realtime extents that belong to this inode's fork. */
diff --git a/fs/xfs/scrub/repair.c b/fs/xfs/scrub/repair.c
index 641b3c8c4e40..c44283b0a502 100644
--- a/fs/xfs/scrub/repair.c
+++ b/fs/xfs/scrub/repair.c
@@ -2246,12 +2246,16 @@ xrep_dotdot_lookup(
 }
 
 #ifdef CONFIG_XFS_RT
-/* Ensure that all rt blocks in the given range are not marked free. */
+/*
+ * Ensure that all rt blocks in the given range are not marked free or
+ * misaligned.
+ */
 int
 xrep_require_rtext_inuse(
 	struct xfs_scrub	*sc,
 	xfs_rtblock_t		rtbno,
-	xfs_filblks_t		len)
+	xfs_filblks_t		len,
+	bool			must_align)
 {
 	struct xfs_mount	*mp = sc->mp;
 	xfs_rtblock_t		startext;
@@ -2262,7 +2266,12 @@ xrep_require_rtext_inuse(
 
 	/* Round the starting rt extent down and the end rt extent up. */
 	startext = div_u64_rem(rtbno, mp->m_sb.sb_rextsize, &mod);
+	if (must_align && mod != 0)
+		return -EFSCORRUPTED;
+
 	endext = div_u64_rem(rtbno + len - 1, mp->m_sb.sb_rextsize, &mod);
+	if (must_align && mod != mp->m_sb.sb_rextsize - 1)
+		return -EFSCORRUPTED;
 
 	error = xfs_rtalloc_extent_is_free(mp, sc->tp, startext,
 			endext - startext + 1, &is_free);
@@ -2293,6 +2302,8 @@ xrep_is_rtmeta_ino(
 	/* Newer rt metadata files are not guaranteed to exist */
 	if (sc->mp->m_rrmapip && ino == sc->mp->m_rrmapip->i_ino)
 		return true;
+	if (sc->mp->m_rrefcountip && ino == sc->mp->m_rrefcountip->i_ino)
+		return true;
 
 	return false;
 }
diff --git a/fs/xfs/scrub/repair.h b/fs/xfs/scrub/repair.h
index 829d1df0bbdb..74216b2ee7c7 100644
--- a/fs/xfs/scrub/repair.h
+++ b/fs/xfs/scrub/repair.h
@@ -97,9 +97,9 @@ int xrep_check_ino_btree_mapping(struct xfs_scrub *sc,
 
 #ifdef CONFIG_XFS_RT
 int xrep_require_rtext_inuse(struct xfs_scrub *sc, xfs_rtblock_t rtbno,
-		xfs_filblks_t len);
+		xfs_filblks_t len, bool must_align);
 #else
-# define xrep_require_rtext_inuse(sc, rtbno, len)	(-ENOSYS)
+# define xrep_require_rtext_inuse(sc, rtbno, len, align)	(-ENOSYS)
 #endif
 bool xrep_is_rtmeta_ino(struct xfs_scrub *sc, xfs_ino_t ino);
 
@@ -159,10 +159,12 @@ int xrep_quotacheck(struct xfs_scrub *sc);
 int xrep_rtsummary(struct xfs_scrub *sc);
 int xrep_rtbitmap(struct xfs_scrub *sc);
 int xrep_rtrmapbt(struct xfs_scrub *sc);
+int xrep_rtrefcountbt(struct xfs_scrub *sc);
 #else
 # define xrep_rtsummary			xrep_notsupported
 # define xrep_rtbitmap			xrep_notsupported
 # define xrep_rtrmapbt			xrep_notsupported
+# define xrep_rtrefcountbt		xrep_notsupported
 #endif /* CONFIG_XFS_RT */
 
 struct xrep_newbt_resv {
@@ -308,6 +310,7 @@ xrep_setup_rtsummary(struct xfs_scrub *sc, unsigned int *whatever)
 #define xrep_parent			xrep_notsupported
 #define xrep_rtbitmap			xrep_notsupported
 #define xrep_rtrmapbt			xrep_notsupported
+#define xrep_rtrefcountbt		xrep_notsupported
 
 #endif /* CONFIG_XFS_ONLINE_REPAIR */
 
diff --git a/fs/xfs/scrub/rtrefcount_repair.c b/fs/xfs/scrub/rtrefcount_repair.c
new file mode 100644
index 000000000000..6b0cb3dcaa4b
--- /dev/null
+++ b/fs/xfs/scrub/rtrefcount_repair.c
@@ -0,0 +1,741 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2021 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_defer.h"
+#include "xfs_btree.h"
+#include "xfs_bit.h"
+#include "xfs_log_format.h"
+#include "xfs_trans.h"
+#include "xfs_sb.h"
+#include "xfs_alloc.h"
+#include "xfs_ialloc.h"
+#include "xfs_rmap.h"
+#include "xfs_rmap_btree.h"
+#include "xfs_rtrmap_btree.h"
+#include "xfs_refcount.h"
+#include "xfs_rtrefcount_btree.h"
+#include "xfs_error.h"
+#include "xfs_health.h"
+#include "xfs_inode.h"
+#include "xfs_quota.h"
+#include "xfs_rtalloc.h"
+#include "xfs_ag.h"
+#include "scrub/xfs_scrub.h"
+#include "scrub/scrub.h"
+#include "scrub/common.h"
+#include "scrub/btree.h"
+#include "scrub/trace.h"
+#include "scrub/repair.h"
+#include "scrub/bitmap.h"
+#include "scrub/xfarray.h"
+
+/*
+ * Rebuilding the Reference Count Btree
+ * ====================================
+ *
+ * This algorithm is "borrowed" from xfs_repair.  Imagine the rmap
+ * entries as rectangles representing extents of physical blocks, and
+ * that the rectangles can be laid down to allow them to overlap each
+ * other; then we know that we must emit a refcnt btree entry wherever
+ * the amount of overlap changes, i.e. the emission stimulus is
+ * level-triggered:
+ *
+ *                 -    ---
+ *       --      ----- ----   ---        ------
+ * --   ----     ----------- ----     ---------
+ * -------------------------------- -----------
+ * ^ ^  ^^ ^^    ^ ^^ ^^^  ^^^^  ^ ^^ ^  ^     ^
+ * 2 1  23 21    3 43 234  2123  1 01 2  3     0
+ *
+ * For our purposes, a rmap is a tuple (startblock, len, fileoff, owner).
+ *
+ * Note that in the actual refcnt btree we don't store the refcount < 2
+ * cases because the bnobt tells us which blocks are free; single-use
+ * blocks aren't recorded in the bnobt or the refcntbt.  If the rmapbt
+ * supports storing multiple entries covering a given block we could
+ * theoretically dispense with the refcntbt and simply count rmaps, but
+ * that's inefficient in the (hot) write path, so we'll take the cost of
+ * the extra tree to save time.  Also there's no guarantee that rmap
+ * will be enabled.
+ *
+ * Given an array of rmaps sorted by physical block number, a starting
+ * physical block (sp), a bag to hold rmaps that cover sp, and the next
+ * physical block where the level changes (np), we can reconstruct the
+ * rt refcount btree as follows:
+ *
+ * While there are still unprocessed rmaps in the array,
+ *  - Set sp to the physical block (pblk) of the next unprocessed rmap.
+ *  - Add to the bag all rmaps in the array where startblock == sp.
+ *  - Set np to the physical block where the bag size will change.  This
+ *    is the minimum of (the pblk of the next unprocessed rmap) and
+ *    (startblock + len of each rmap in the bag).
+ *  - Record the bag size as old_bag_size.
+ *
+ *  - While the bag isn't empty,
+ *     - Remove from the bag all rmaps where startblock + len == np.
+ *     - Add to the bag all rmaps in the array where startblock == np.
+ *     - If the bag size isn't old_bag_size, store the refcount entry
+ *       (sp, np - sp, bag_size) in the refcnt btree.
+ *     - If the bag is empty, break out of the inner loop.
+ *     - Set old_bag_size to the bag size
+ *     - Set sp = np.
+ *     - Set np to the physical block where the bag size will change.
+ *       This is the minimum of (the pblk of the next unprocessed rmap)
+ *       and (startblock + len of each rmap in the bag).
+ *
+ * Like all the other repairers, we make a list of all the refcount
+ * records we need, then reinitialize the rt refcount btree root and
+ * insert all the records.
+ */
+
+/* The only parts of the rmap that we care about for computing refcounts. */
+struct xrep_rtrefc_rmap {
+	xfs_rtblock_t		startblock;
+	xfs_filblks_t		blockcount;
+} __packed;
+
+struct xrep_rtrefc {
+	/* refcount extents */
+	struct xfarray		*refcount_records;
+
+	/* new refcountbt information */
+	struct xrep_newbt	new_btree_info;
+	struct xfs_btree_bload	rtrefc_bload;
+
+	/* old refcountbt blocks */
+	struct xbitmap		old_rtrefcountbt_blocks;
+
+	struct xfs_scrub	*sc;
+
+	/* # of refcountbt blocks */
+	xfs_filblks_t		btblocks;
+
+	/* get_record()'s position in the free space record array. */
+	uint64_t		iter;
+};
+
+/* Check for any obvious conflicts with this shared/CoW staging extent. */
+STATIC int
+xrep_rtrefc_check_ext(
+	struct xfs_scrub		*sc,
+	const struct xfs_refcount_irec	*rec)
+{
+	xfs_rtblock_t			rtbno = rec->rc_startblock;
+
+	if (rtbno >= XFS_RTREFC_COW_START)
+		rtbno -= XFS_RTREFC_COW_START;
+
+	/* Must be within the rt device. */
+	if (!xfs_verify_rtext(sc->mp, rtbno, rec->rc_blockcount))
+		return -EFSCORRUPTED;
+
+	/* Make sure this isn't free space or misaligned. */
+	return xrep_require_rtext_inuse(sc, rtbno, rec->rc_blockcount, true);
+}
+
+/* Record a reference count extent. */
+STATIC int
+xrep_rtrefc_stash(
+	struct xrep_rtrefc		*rr,
+	xfs_rtblock_t			bno,
+	xfs_filblks_t			len,
+	xfs_nlink_t			refcount)
+{
+	struct xfs_refcount_irec	irec = {
+		.rc_startblock		= bno,
+		.rc_blockcount		= len,
+		.rc_refcount		= refcount,
+	};
+	struct xfs_mount		*mp = rr->sc->mp;
+	int				error = 0;
+
+	if (xchk_should_terminate(rr->sc, &error))
+		return error;
+
+	error = xrep_rtrefc_check_ext(rr->sc, &irec);
+	if (error)
+		return error;
+
+	trace_xrep_rtrefc_found(mp, &irec);
+
+	return xfarray_append(rr->refcount_records, &irec);
+}
+
+/* Record a CoW staging extent. */
+STATIC int
+xrep_rtrefc_stash_cow(
+	struct xrep_rtrefc		*rr,
+	xfs_rtblock_t			bno,
+	xfs_filblks_t			len)
+{
+	return xrep_rtrefc_stash(rr, bno + XFS_RTREFC_COW_START, len, 1);
+}
+
+/* Decide if an rmap could describe a shared extent. */
+static inline bool
+xrep_rtrefc_rmap_shareable(
+	const struct xfs_rmap_irec	*rmap)
+{
+	/* rt metadata are never sharable */
+	if (XFS_RMAP_NON_INODE_OWNER(rmap->rm_owner))
+		return false;
+
+	/* Unwritten file blocks are not shareable. */
+	if (rmap->rm_flags & XFS_RMAP_UNWRITTEN)
+		return false;
+
+	return true;
+}
+
+/* Grab the next (abbreviated) rmap record from the rmapbt. */
+STATIC int
+xrep_rtrefc_walk_rmaps(
+	struct xrep_rtrefc	*rr,
+	struct xrep_rtrefc_rmap	*rrm,
+	bool			*have_rec)
+{
+	struct xfs_rmap_irec	rmap;
+	struct xfs_btree_cur	*cur = rr->sc->sr.rmap_cur;
+	struct xfs_mount	*mp = cur->bc_mp;
+	int			have_gt;
+	int			error = 0;
+
+	*have_rec = false;
+
+	/*
+	 * Loop through the remaining rmaps.  Remember CoW staging
+	 * extents and the refcountbt blocks from the old tree for later
+	 * disposal.  We can only share written data fork extents, so
+	 * keep looping until we find an rmap for one.
+	 */
+	do {
+		if (xchk_should_terminate(rr->sc, &error))
+			return error;
+
+		error = xfs_btree_increment(cur, 0, &have_gt);
+		if (error)
+			return error;
+		if (!have_gt)
+			return 0;
+
+		error = xfs_rmap_get_rec(cur, &rmap, &have_gt);
+		if (error)
+			return error;
+		if (XFS_IS_CORRUPT(mp, !have_gt)) {
+			xfs_btree_mark_sick(cur);
+			return -EFSCORRUPTED;
+		}
+
+		if (rmap.rm_owner == XFS_RMAP_OWN_COW) {
+			error = xrep_rtrefc_stash_cow(rr, rmap.rm_startblock,
+					rmap.rm_blockcount);
+			if (error)
+				return error;
+		} else if (xfs_internal_inum(mp, rmap.rm_owner) ||
+			   (rmap.rm_flags & (XFS_RMAP_ATTR_FORK |
+					     XFS_RMAP_BMBT_BLOCK))) {
+			xfs_btree_mark_sick(cur);
+			return -EFSCORRUPTED;
+		}
+
+	} while (!xrep_rtrefc_rmap_shareable(&rmap));
+
+	rrm->startblock = rmap.rm_startblock;
+	rrm->blockcount = rmap.rm_blockcount;
+	*have_rec = true;
+	return 0;
+}
+
+/* Compare two btree extents. */
+static int
+xrep_rtrefc_extent_cmp(
+	const void			*a,
+	const void			*b)
+{
+	const struct xfs_refcount_irec	*ap = a;
+	const struct xfs_refcount_irec	*bp = b;
+
+	if (ap->rc_startblock > bp->rc_startblock)
+		return 1;
+	else if (ap->rc_startblock < bp->rc_startblock)
+		return -1;
+	return 0;
+}
+
+#define RRM_NEXT(r)	((r).startblock + (r).blockcount)
+/*
+ * Find the next block where the refcount changes, given the next rmap we
+ * looked at and the ones we're already tracking.
+ */
+static inline int
+xrep_rtrefc_next_edge(
+	struct xfarray		*rmap_bag,
+	struct xrep_rtrefc_rmap	*next_rrm,
+	bool			next_valid,
+	xfs_rtblock_t		*nbnop)
+{
+	struct xrep_rtrefc_rmap	rrm;
+	uint64_t		i = 0;
+	xfs_rtblock_t		nbno = NULLFSBLOCK;
+	int			error;
+
+	if (next_valid)
+		nbno = next_rrm->startblock;
+
+	while ((error = xfarray_iter(rmap_bag, &i, &rrm)) == 1)
+		nbno = min_t(xfs_rtblock_t, nbno, RRM_NEXT(rrm));
+
+	if (error)
+		return error;
+
+	/*
+	 * We should have found /something/ because either next_rrm is the next
+	 * interesting rmap to look at after emitting this refcount extent, or
+	 * there are other rmaps in rmap_bag contributing to the current
+	 * sharing count.  But if something is seriously wrong, bail out.
+	 */
+	if (nbno == NULLFSBLOCK)
+		return -EFSCORRUPTED;
+
+	*nbnop = nbno;
+	return 0;
+}
+
+/* Record extents that belong to the realtime refcount inode. */
+STATIC int
+xrep_rtrefc_walk_rmap(
+	struct xfs_btree_cur		*cur,
+	const struct xfs_rmap_irec	*rec,
+	void				*priv)
+{
+	struct xrep_rtrefc		*rr = priv;
+	struct xfs_mount		*mp = cur->bc_mp;
+	xfs_fsblock_t			fsbno;
+	int				error = 0;
+
+	if (xchk_should_terminate(rr->sc, &error))
+		return error;
+
+	/* Skip extents which are not owned by this inode and fork. */
+	if (rec->rm_owner != mp->m_rrefcountip->i_ino)
+		return 0;
+
+	error = xrep_check_ino_btree_mapping(rr->sc, rec);
+	if (error)
+		return error;
+
+	fsbno = XFS_AGB_TO_FSB(mp, cur->bc_ag.pag->pag_agno,
+			rec->rm_startblock);
+
+	return xbitmap_set(&rr->old_rtrefcountbt_blocks, fsbno,
+			rec->rm_blockcount);
+}
+
+/*
+ * Walk forward through the rmap btree to collect all rmaps starting at
+ * @bno in @rmap_bag.  These represent the file(s) that share ownership of
+ * the current block.  Upon return, the rmap cursor points to the last record
+ * satisfying the startblock constraint.
+ */
+static int
+xrep_rtrefc_push_rmaps_at(
+	struct xrep_rtrefc	*rr,
+	struct xfarray		*rmap_bag,
+	xfs_fsblock_t		bno,
+	struct xrep_rtrefc_rmap	*rrm,
+	bool			*have,
+	size_t			*stack_sz)
+{
+	struct xfs_scrub	*sc = rr->sc;
+	int			have_gt;
+	int			error;
+
+	while (*have && rrm->startblock == bno) {
+		error = xfarray_store_anywhere(rmap_bag, rrm);
+		if (error)
+			return error;
+		(*stack_sz)++;
+		error = xrep_rtrefc_walk_rmaps(rr, rrm, have);
+		if (error)
+			return error;
+	}
+
+	error = xfs_btree_decrement(sc->sr.rmap_cur, 0, &have_gt);
+	if (error)
+		return error;
+	if (XFS_IS_CORRUPT(sc->mp, !have_gt)) {
+		xfs_btree_mark_sick(sc->sr.rmap_cur);
+		return -EFSCORRUPTED;
+	}
+
+	return 0;
+}
+
+/* Scan one AG for reverse mappings for the realtime refcount btree. */
+STATIC int
+xrep_rtrefc_scan_ag(
+	struct xrep_rtrefc	*rr,
+	struct xfs_perag	*pag)
+{
+	struct xfs_scrub	*sc = rr->sc;
+	int			error;
+
+	error = xrep_ag_init(sc, pag, &sc->sa);
+	if (error)
+		return error;
+
+	error = xfs_rmap_query_all(sc->sa.rmap_cur, xrep_rtrefc_walk_rmap, rr);
+	xchk_ag_free(sc, &sc->sa);
+	return error;
+}
+
+/* Iterate all the rmap records to generate reference count data. */
+STATIC int
+xrep_rtrefc_find_refcounts(
+	struct xrep_rtrefc	*rr)
+{
+	struct xrep_rtrefc_rmap	rrm;
+	struct xfs_scrub	*sc = rr->sc;
+	struct xfarray		*rmap_bag;
+	struct xfs_perag	*pag;
+	xfs_rtblock_t		sbno;
+	xfs_rtblock_t		cbno;
+	xfs_rtblock_t		nbno;
+	size_t			old_stack_sz;
+	size_t			stack_sz = 0;
+	xfs_agnumber_t		agno;
+	bool			have;
+	int			error;
+
+	/* Scan for old rtrefc btree blocks. */
+	for_each_perag(sc->mp, agno, pag) {
+		error = xrep_rtrefc_scan_ag(rr, pag);
+		if (error) {
+			xfs_perag_put(pag);
+			return error;
+		}
+	}
+
+	xrep_rt_btcur_init(sc, &sc->sr);
+
+	/* Set up some storage */
+	error = xfarray_create(sc->mp, "rtrmap bag",
+			sizeof(struct xrep_rtrefc_rmap), &rmap_bag);
+	if (error)
+		goto out_cur;
+
+	/* Start the rtrmapbt cursor to the left of all records. */
+	error = xfs_btree_goto_left_edge(sc->sr.rmap_cur);
+	if (error)
+		goto out_bag;
+
+	/* Process reverse mappings into refcount data. */
+	while (xfs_btree_has_more_records(sc->sr.rmap_cur)) {
+		/* Push all rmaps with pblk == sbno onto the stack */
+		error = xrep_rtrefc_walk_rmaps(rr, &rrm, &have);
+		if (error)
+			goto out_bag;
+		if (!have)
+			break;
+		sbno = cbno = rrm.startblock;
+		error = xrep_rtrefc_push_rmaps_at(rr, rmap_bag, sbno,
+					&rrm, &have, &stack_sz);
+		if (error)
+			goto out_bag;
+
+		/* Set nbno to the bno of the next refcount change */
+		error = xrep_rtrefc_next_edge(rmap_bag, &rrm, have, &nbno);
+		if (error)
+			goto out_bag;
+
+		ASSERT(nbno > sbno);
+		old_stack_sz = stack_sz;
+
+		/* While stack isn't empty... */
+		while (stack_sz) {
+			uint64_t	i = 0;
+
+			/* Pop all rmaps that end at nbno */
+			while ((error = xfarray_iter(rmap_bag, &i,
+								&rrm)) == 1) {
+				if (RRM_NEXT(rrm) != nbno)
+					continue;
+				error = xfarray_nullify(rmap_bag, i - 1);
+				if (error)
+					goto out_bag;
+				stack_sz--;
+			}
+			if (error)
+				goto out_bag;
+
+			/* Push array items that start at nbno */
+			error = xrep_rtrefc_walk_rmaps(rr, &rrm, &have);
+			if (error)
+				goto out_bag;
+			if (have) {
+				error = xrep_rtrefc_push_rmaps_at(rr, rmap_bag,
+						nbno, &rrm, &have, &stack_sz);
+				if (error)
+					goto out_bag;
+			}
+
+			/* Emit refcount if necessary */
+			ASSERT(nbno > cbno);
+			if (stack_sz != old_stack_sz) {
+				if (old_stack_sz > 1) {
+					error = xrep_rtrefc_stash(rr, cbno,
+							nbno - cbno,
+							old_stack_sz);
+					if (error)
+						goto out_bag;
+				}
+				cbno = nbno;
+			}
+
+			/* Stack empty, go find the next rmap */
+			if (stack_sz == 0)
+				break;
+			old_stack_sz = stack_sz;
+			sbno = nbno;
+
+			/* Set nbno to the bno of the next refcount change */
+			error = xrep_rtrefc_next_edge(rmap_bag, &rrm, have,
+					&nbno);
+			if (error)
+				goto out_bag;
+
+			ASSERT(nbno > sbno);
+		}
+	}
+
+	ASSERT(stack_sz == 0);
+out_bag:
+	xfarray_destroy(rmap_bag);
+out_cur:
+	xchk_rt_btcur_free(&sc->sr);
+	return error;
+}
+#undef RRM_NEXT
+
+/* Retrieve refcountbt data for bulk load. */
+STATIC int
+xrep_rtrefc_get_record(
+	struct xfs_btree_cur		*cur,
+	void				*priv)
+{
+	struct xrep_rtrefc		*rr = priv;
+
+	return xfarray_load_next(rr->refcount_records, &rr->iter,
+			&cur->bc_rec.rc);
+}
+
+/* Feed one of the new btree blocks to the bulk loader. */
+STATIC int
+xrep_rtrefc_claim_block(
+	struct xfs_btree_cur	*cur,
+	union xfs_btree_ptr	*ptr,
+	void			*priv)
+{
+	struct xrep_rtrefc        *rr = priv;
+	int			error;
+
+	error = xrep_newbt_relog_efis(&rr->new_btree_info);
+	if (error)
+		return error;
+
+	return xrep_newbt_claim_block(cur, &rr->new_btree_info, ptr);
+}
+
+/* Figure out how much space we need to create the incore btree root block. */
+STATIC size_t
+xrep_rtrefc_iroot_size(
+	struct xfs_btree_cur	*cur,
+	unsigned int		level,
+	unsigned int		nr_this_level,
+	void			*priv)
+{
+	return xfs_rtrefcount_broot_space_calc(cur->bc_mp, level,
+			nr_this_level);
+}
+
+/*
+ * Use the collected refcount information to stage a new rt refcount btree.  If
+ * this is successful we'll return with the new btree root information logged
+ * to the repair transaction but not yet committed.
+ */
+STATIC int
+xrep_rtrefc_build_new_tree(
+	struct xrep_rtrefc	*rr)
+{
+	struct xfs_owner_info	oinfo;
+	struct xfs_scrub	*sc = rr->sc;
+	struct xfs_mount	*mp = sc->mp;
+	struct xfs_btree_cur	*refc_cur;
+	int			error;
+
+	rr->rtrefc_bload.get_record = xrep_rtrefc_get_record;
+	rr->rtrefc_bload.claim_block = xrep_rtrefc_claim_block;
+	rr->rtrefc_bload.iroot_size = xrep_rtrefc_iroot_size;
+	xrep_bload_estimate_slack(sc, &rr->rtrefc_bload);
+
+	/*
+	 * Sort the refcount extents by startblock or else the btree records
+	 * will be in the wrong order.
+	 */
+	error = xfarray_sort(rr->refcount_records, xrep_rtrefc_extent_cmp);
+	if (error)
+		return error;
+
+	/*
+	 * Prepare to construct the new btree by reserving disk space for the
+	 * new btree and setting up all the accounting information we'll need
+	 * to root the new btree while it's under construction and before we
+	 * attach it to the realtime refcount inode.
+	 */
+	xfs_rmap_ino_bmbt_owner(&oinfo, mp->m_rrefcountip->i_ino,
+			XFS_DATA_FORK);
+	xrep_newbt_init_inode(&rr->new_btree_info, sc, XFS_DATA_FORK, &oinfo);
+	refc_cur = xfs_rtrefcountbt_stage_cursor(mp, mp->m_rrefcountip,
+			&rr->new_btree_info.ifake);
+
+	/* Compute how many blocks we'll need. */
+	error = xfs_btree_bload_compute_geometry(refc_cur, &rr->rtrefc_bload,
+			xfarray_length(rr->refcount_records));
+	if (error)
+		goto err_cur;
+
+	/* Last chance to abort before we start committing fixes. */
+	if (xchk_should_terminate(sc, &error))
+		goto err_cur;
+
+	/*
+	 * Guess how many blocks we're going to need to rebuild an entire
+	 * rtrefcountbt from the number of extents we found, and pump up our
+	 * transaction to have sufficient block reservation.
+	 */
+	error = xfs_trans_reserve_more_inode(sc->tp, mp->m_rrefcountip,
+			rr->rtrefc_bload.nr_blocks, 0);
+	if (error)
+		goto err_cur;
+
+	/* Reserve the space we'll need for the new btree. */
+	error = xrep_newbt_alloc_blocks(&rr->new_btree_info,
+			rr->rtrefc_bload.nr_blocks);
+	if (error)
+		goto err_cur;
+
+	/* Add all observed refcount records. */
+	rr->new_btree_info.ifake.if_fork->if_format = XFS_DINODE_FMT_REFCOUNT;
+	rr->iter = 0;
+	error = xfs_btree_bload(refc_cur, &rr->rtrefc_bload, rr);
+	if (error)
+		goto err_cur;
+
+	/*
+	 * Install the new rtrefc btree in the inode.  After this point the old
+	 * btree is no longer accessible, the new tree is live, and we can
+	 * delete the cursor.
+	 */
+	xfs_rtrefcountbt_commit_staged_btree(refc_cur, sc->tp);
+	xrep_inode_set_nblocks(rr->sc, rr->new_btree_info.ifake.if_blocks);
+	xfs_btree_del_cursor(refc_cur, 0);
+
+	/* Dispose of any unused blocks and the accounting information. */
+	xrep_newbt_destroy(&rr->new_btree_info, error);
+	return xrep_roll_trans(sc);
+err_cur:
+	xfs_btree_del_cursor(refc_cur, error);
+	xrep_newbt_destroy(&rr->new_btree_info, error);
+	return error;
+}
+
+/*
+ * Now that we've logged the roots of the new btrees, invalidate all of the
+ * old blocks and free them.
+ */
+STATIC int
+xrep_rtrefc_remove_old_tree(
+	struct xrep_rtrefc	*rr)
+{
+	struct xfs_owner_info	oinfo;
+	int			error;
+
+	xfs_rmap_ino_bmbt_owner(&oinfo, rr->sc->ip->i_ino, XFS_DATA_FORK);
+
+	/*
+	 * Free all the extents that were allocated to the former rtrefcountbt
+	 * and aren't cross-linked with something else.  If the incore space
+	 * reservation for the rtrmap inode is insufficient, this will refill
+	 * it.
+	 */
+	error = xrep_reap_extents(rr->sc, &rr->old_rtrefcountbt_blocks, &oinfo,
+			XFS_AG_RESV_IMETA);
+	if (error)
+		return error;
+
+	/*
+	 * Ensure the proper reservation for the rtrefcount inode so that we
+	 * don't fail to expand the btree.
+	 */
+	return xrep_reset_imeta_reservation(rr->sc);
+}
+
+/* Rebuild the rt refcount btree. */
+int
+xrep_rtrefcountbt(
+	struct xfs_scrub	*sc)
+{
+	struct xrep_rtrefc	*rr;
+	struct xfs_mount	*mp = sc->mp;
+	int			error;
+
+	/* We require the rmapbt to rebuild anything. */
+	if (!xfs_has_rtrmapbt(mp))
+		return -EOPNOTSUPP;
+
+	rr = kmem_zalloc(sizeof(struct xrep_rtrefc), KM_NOFS | KM_MAYFAIL);
+	if (!rr)
+		return -ENOMEM;
+	rr->sc = sc;
+
+	/* Set up some storage */
+	error = xfarray_create(sc->mp, "rtrefcount records",
+			sizeof(struct xfs_refcount_irec),
+			&rr->refcount_records);
+	if (error)
+		goto out_rr;
+
+	/* Collect all reference counts. */
+	xbitmap_init(&rr->old_rtrefcountbt_blocks);
+	error = xrep_rtrefc_find_refcounts(rr);
+	if (error)
+		goto out_bitmap;
+
+	xfs_trans_ijoin(sc->tp, sc->ip, 0);
+	error = xrep_ino_dqattach(sc);
+	if (error)
+		goto out_bitmap;
+
+	/* Rebuild the refcount information. */
+	error = xrep_rtrefc_build_new_tree(rr);
+	if (error)
+		goto out_bitmap;
+
+	/* Kill the old tree. */
+	error = xrep_rtrefc_remove_old_tree(rr);
+
+out_bitmap:
+	xbitmap_destroy(&rr->old_rtrefcountbt_blocks);
+	xfarray_destroy(rr->refcount_records);
+out_rr:
+	kmem_free(rr);
+	return error;
+}
diff --git a/fs/xfs/scrub/rtrmap_repair.c b/fs/xfs/scrub/rtrmap_repair.c
index e0f83af104de..03a28e733877 100644
--- a/fs/xfs/scrub/rtrmap_repair.c
+++ b/fs/xfs/scrub/rtrmap_repair.c
@@ -153,7 +153,7 @@ xrep_rtrmap_check_mapping(
 
 	/* Make sure this isn't free space. */
 	return xrep_require_rtext_inuse(sc, rec->rm_startblock,
-			rec->rm_blockcount);
+			rec->rm_blockcount, false);
 }
 
 /* Store a reverse-mapping record. */
diff --git a/fs/xfs/scrub/scrub.c b/fs/xfs/scrub/scrub.c
index 160480548461..0c5f8b0995b6 100644
--- a/fs/xfs/scrub/scrub.c
+++ b/fs/xfs/scrub/scrub.c
@@ -390,7 +390,7 @@ static const struct xchk_meta_ops meta_scrub_ops[] = {
 		.setup	= xchk_setup_rtrefcountbt,
 		.scrub	= xchk_rtrefcountbt,
 		.has	= xfs_has_rtreflink,
-		.repair	= xrep_notsupported,
+		.repair	= xrep_rtrefcountbt,
 	},
 };
 
diff --git a/fs/xfs/scrub/trace.h b/fs/xfs/scrub/trace.h
index bca2d61dc1ad..d5901bbf4480 100644
--- a/fs/xfs/scrub/trace.h
+++ b/fs/xfs/scrub/trace.h
@@ -1969,6 +1969,31 @@ TRACE_EVENT(xrep_rtrmap_found,
 		  __entry->flags)
 );
 
+TRACE_EVENT(xrep_rtrefc_found,
+	TP_PROTO(struct xfs_mount *mp, const struct xfs_refcount_irec *rec),
+	TP_ARGS(mp, rec),
+	TP_STRUCT__entry(
+		__field(dev_t, dev)
+		__field(dev_t, rtdev)
+		__field(xfs_fsblock_t, startblock)
+		__field(xfs_filblks_t, blockcount)
+		__field(xfs_nlink_t, refcount)
+	),
+	TP_fast_assign(
+		__entry->dev = mp->m_super->s_dev;
+		__entry->rtdev = mp->m_rtdev_targp->bt_dev;
+		__entry->startblock = rec->rc_startblock;
+		__entry->blockcount = rec->rc_blockcount;
+		__entry->refcount = rec->rc_refcount;
+	),
+	TP_printk("dev %d:%d rtdev %d:%d rtbno 0x%llx fsbcount 0x%llx refcount %u",
+		  MAJOR(__entry->dev), MINOR(__entry->dev),
+		  MAJOR(__entry->rtdev), MINOR(__entry->rtdev),
+		  __entry->startblock,
+		  __entry->blockcount,
+		  __entry->refcount)
+)
+
 #endif /* IS_ENABLED(CONFIG_XFS_ONLINE_REPAIR) */
 
 #endif /* _TRACE_XFS_SCRUB_TRACE_H */