FAILED: patch "[PATCH] xfs: snapshot old AGFL before rewriting it" failed to apply to 5.15-stable tree

index 2104512f1ee1..46c95354ca64 100644
@@ -668,14 +668,16 @@ xrep_agfl_init_header(
 	struct xfs_scrub	*sc,
 	struct xfs_buf		*agfl_bp,
 	struct xagb_bitmap	*agfl_extents,
-	xfs_agblock_t		flcount)
+	xfs_agblock_t		flcount,
+	struct xfs_agfl		*old_agfl)
 {
 	struct xrep_agfl_fill	af = {
 		.sc		= sc,
 		.flcount	= flcount,
 	};
 	struct xfs_mount	*mp = sc->mp;
-	struct xfs_agfl		*agfl;
+	struct xfs_agfl		*agfl = XFS_BUF_TO_AGFL(agfl_bp);
+	const size_t		agfl_sz = BBTOB(agfl_bp->b_length);
 	int			error;
 
 	ASSERT(flcount <= xfs_agfl_size(mp));

@@ -684,8 +686,8 @@ xrep_agfl_init_header(
 	 * Start rewriting the header by setting the bno[] array to
 	 * NULLAGBLOCK, then setting AGFL header fields.
 	 */
-	agfl = XFS_BUF_TO_AGFL(agfl_bp);
-	memset(agfl, 0xFF, BBTOB(agfl_bp->b_length));
+	memcpy(old_agfl, agfl, agfl_sz);
+	memset(agfl, 0xFF, agfl_sz);
 	agfl->agfl_magicnum = cpu_to_be32(XFS_AGFL_MAGIC);
 	agfl->agfl_seqno = cpu_to_be32(pag_agno(sc->sa.pag));
 	uuid_copy(&agfl->agfl_uuid, &mp->m_sb.sb_meta_uuid);

@@ -700,13 +702,18 @@ xrep_agfl_init_header(
 	xagb_bitmap_walk(agfl_extents, xrep_agfl_fill, &af);
 	error = xagb_bitmap_disunion(agfl_extents, &af.used_extents);
 	if (error)
-		return error;
+		goto err_undo;
 
 	/* Write new AGFL to disk. */
 	xfs_trans_buf_set_type(sc->tp, agfl_bp, XFS_BLFT_AGFL_BUF);
-	xfs_trans_log_buf(sc->tp, agfl_bp, 0, BBTOB(agfl_bp->b_length) - 1);
+	xfs_trans_log_buf(sc->tp, agfl_bp, 0, agfl_sz - 1);
 	xagb_bitmap_destroy(&af.used_extents);
 	return 0;
+
+err_undo:
+	xagb_bitmap_destroy(&af.used_extents);
+	memcpy(agfl, old_agfl, agfl_sz);
+	return error;
 }
 
 /* Repair the AGFL. */

@@ -718,6 +725,7 @@ xrep_agfl(
 	struct xfs_mount	*mp = sc->mp;
 	struct xfs_buf		*agf_bp;
 	struct xfs_buf		*agfl_bp;
+	struct xfs_agfl		*old_agfl;
 	xfs_agblock_t		flcount;
 	int			error;
 

@@ -725,6 +733,10 @@ xrep_agfl(
 	if (!xfs_has_rmapbt(mp))
 		return -EOPNOTSUPP;
 
+	old_agfl = kzalloc(BBTOB(XFS_FSS_TO_BB(mp, 1)), XCHK_GFP_FLAGS);
+	if (!old_agfl)
+		return -ENOMEM;
+
 	xagb_bitmap_init(&agfl_extents);
 
 	/*

@@ -734,7 +746,7 @@ xrep_agfl(
 	 */
 	error = xfs_alloc_read_agf(sc->sa.pag, sc->tp, 0, &agf_bp);
 	if (error)
-		return error;
+		goto err_old_agfl;
 
 	/*
 	 * Make sure we have the AGFL buffer, as scrub might have decided it

@@ -745,7 +757,7 @@ xrep_agfl(
 						XFS_AGFL_DADDR(mp)),
 			XFS_FSS_TO_BB(mp, 1), 0, &agfl_bp, NULL);
 	if (error)
-		return error;
+		goto err_old_agfl;
 	agfl_bp->b_ops = &xfs_agfl_buf_ops;
 
 	/* Gather all the extents we're going to put on the new AGFL. */

@@ -762,10 +774,11 @@ xrep_agfl(
 	 * we adjust the AGF flcount (which can fail) so avoid updating any
 	 * buffers until we know that part works.
 	 */
-	xrep_agfl_update_agf(sc, agf_bp, flcount);
-	error = xrep_agfl_init_header(sc, agfl_bp, &agfl_extents, flcount);
+	error = xrep_agfl_init_header(sc, agfl_bp, &agfl_extents, flcount,
+			old_agfl);
 	if (error)
 		goto err;
+	xrep_agfl_update_agf(sc, agf_bp, flcount);
 
 	/*
 	 * Ok, the AGFL should be ready to go now.  Roll the transaction to

@@ -785,6 +798,8 @@ xrep_agfl(
 
 err:
 	xagb_bitmap_destroy(&agfl_extents);
+err_old_agfl:
+	kfree(old_agfl);
 	return error;
 }