diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
index 02457e176c42..71b4743ffb77 100644
--- a/fs/xfs/xfs_reflink.c
+++ b/fs/xfs/xfs_reflink.c
@@ -120,38 +120,46 @@
  */
 
 /*
- * Given an AG extent, find the lowest-numbered run of shared blocks
- * within that range and return the range in fbno/flen.  If
- * find_end_of_shared is true, return the longest contiguous extent of
- * shared blocks.  If there are no shared extents, fbno and flen will
- * be set to NULLAGBLOCK and 0, respectively.
+ * Given a file mapping for the data device, find the lowest-numbered run of
+ * shared blocks within that mapping and return it in shared_offset/shared_len.
+ * The offset is relative to the start of irec.
+ *
+ * If find_end_of_shared is true, return the longest contiguous extent of shared
+ * blocks.  If there are no shared extents, shared_offset and shared_len will be
+ * set to 0;
  */
 static int
 xfs_reflink_find_shared(
-	struct xfs_perag	*pag,
+	struct xfs_mount	*mp,
 	struct xfs_trans	*tp,
-	xfs_agblock_t		agbno,
-	xfs_extlen_t		aglen,
-	xfs_agblock_t		*fbno,
-	xfs_extlen_t		*flen,
+	const struct xfs_bmbt_irec *irec,
+	xfs_extlen_t		*shared_offset,
+	xfs_extlen_t		*shared_len,
 	bool			find_end_of_shared)
 {
 	struct xfs_buf		*agbp;
+	struct xfs_perag	*pag;
 	struct xfs_btree_cur	*cur;
 	int			error;
+	xfs_agblock_t		orig_bno, found_bno;
+
+	pag = xfs_perag_get(mp, XFS_FSB_TO_AGNO(mp, irec->br_startblock));
+	orig_bno = XFS_FSB_TO_AGBNO(mp, irec->br_startblock);
 
 	error = xfs_alloc_read_agf(pag, tp, 0, &agbp);
 	if (error)
-		return error;
-
-	cur = xfs_refcountbt_init_cursor(pag_mount(pag), tp, agbp, pag);
-
-	error = xfs_refcount_find_shared(cur, agbno, aglen, fbno, flen,
-			find_end_of_shared);
+		goto out;
 
+	cur = xfs_refcountbt_init_cursor(mp, tp, agbp, pag);
+	error = xfs_refcount_find_shared(cur, orig_bno, irec->br_blockcount,
+			&found_bno, shared_len, find_end_of_shared);
 	xfs_btree_del_cursor(cur, error);
-
 	xfs_trans_brelse(tp, agbp);
+
+	if (!error && *shared_len)
+		*shared_offset = found_bno - orig_bno;
+out:
+	xfs_perag_put(pag);
 	return error;
 }
 
@@ -172,11 +180,7 @@ xfs_reflink_trim_around_shared(
 	bool			*shared)
 {
 	struct xfs_mount	*mp = ip->i_mount;
-	struct xfs_perag	*pag;
-	xfs_agblock_t		agbno;
-	xfs_extlen_t		aglen;
-	xfs_agblock_t		fbno;
-	xfs_extlen_t		flen;
+	xfs_extlen_t		shared_offset, shared_len;
 	int			error = 0;
 
 	/* Holes, unwritten, and delalloc extents cannot be shared */
@@ -187,41 +191,33 @@ xfs_reflink_trim_around_shared(
 
 	trace_xfs_reflink_trim_around_shared(ip, irec);
 
-	pag = xfs_perag_get(mp, XFS_FSB_TO_AGNO(mp, irec->br_startblock));
-	agbno = XFS_FSB_TO_AGBNO(mp, irec->br_startblock);
-	aglen = irec->br_blockcount;
-
-	error = xfs_reflink_find_shared(pag, NULL, agbno, aglen, &fbno, &flen,
-			true);
-	xfs_perag_put(pag);
+	error = xfs_reflink_find_shared(mp, NULL, irec, &shared_offset,
+			&shared_len, true);
 	if (error)
 		return error;
 
-	*shared = false;
-	if (fbno == NULLAGBLOCK) {
+	if (!shared_len) {
 		/* No shared blocks at all. */
-		return 0;
-	}
-
-	if (fbno == agbno) {
+		*shared = false;
+	} else if (!shared_offset) {
 		/*
-		 * The start of this extent is shared.  Truncate the
-		 * mapping at the end of the shared region so that a
-		 * subsequent iteration starts at the start of the
-		 * unshared region.
+		 * The start of this mapping points to shared space.  Truncate
+		 * the mapping at the end of the shared region so that a
+		 * subsequent iteration starts at the start of the unshared
+		 * region.
 		 */
-		irec->br_blockcount = flen;
+		irec->br_blockcount = shared_len;
 		*shared = true;
-		return 0;
+	} else {
+		/*
+		 * There's a shared region that doesn't start at the beginning
+		 * of the mapping.  Truncate the mapping at the start of the
+		 * shared extent so that a subsequent iteration starts at the
+		 * start of the shared region.
+		 */
+		irec->br_blockcount = shared_offset;
+		*shared = false;
 	}
-
-	/*
-	 * There's a shared extent midway through this extent.
-	 * Truncate the mapping at the start of the shared
-	 * extent so that a subsequent iteration starts at the
-	 * start of the shared region.
-	 */
-	irec->br_blockcount = fbno - agbno;
 	return 0;
 }
 
@@ -1552,27 +1548,19 @@ xfs_reflink_inode_has_shared_extents(
 	*has_shared = false;
 	found = xfs_iext_lookup_extent(ip, ifp, 0, &icur, &got);
 	while (found) {
-		struct xfs_perag	*pag;
-		xfs_agblock_t		agbno;
-		xfs_extlen_t		aglen;
-		xfs_agblock_t		rbno;
-		xfs_extlen_t		rlen;
+		xfs_extlen_t		shared_offset, shared_len;
 
 		if (isnullstartblock(got.br_startblock) ||
 		    got.br_state != XFS_EXT_NORM)
 			goto next;
 
-		pag = xfs_perag_get(mp, XFS_FSB_TO_AGNO(mp, got.br_startblock));
-		agbno = XFS_FSB_TO_AGBNO(mp, got.br_startblock);
-		aglen = got.br_blockcount;
-		error = xfs_reflink_find_shared(pag, tp, agbno, aglen,
-				&rbno, &rlen, false);
-		xfs_perag_put(pag);
+		error = xfs_reflink_find_shared(mp, tp, &got, &shared_offset,
+				&shared_len, false);
 		if (error)
 			return error;
 
 		/* Is there still a shared block here? */
-		if (rbno != NULLAGBLOCK) {
+		if (shared_len) {
 			*has_shared = true;
 			return 0;
 		}
diff --git a/fs/xfs/xfs_reflink.h b/fs/xfs/xfs_reflink.h
index 4a58e4533671..3bfd7ab9e114 100644
--- a/fs/xfs/xfs_reflink.h
+++ b/fs/xfs/xfs_reflink.h
@@ -25,7 +25,7 @@ xfs_can_free_cowblocks(struct xfs_inode *ip)
 	return true;
 }
 
-extern int xfs_reflink_trim_around_shared(struct xfs_inode *ip,
+int xfs_reflink_trim_around_shared(struct xfs_inode *ip,
 		struct xfs_bmbt_irec *irec, bool *shared);
 int xfs_bmap_trim_cow(struct xfs_inode *ip, struct xfs_bmbt_irec *imap,
 		bool *shared);