xfs: reset rootdir extent size hint after growfsrt

If growfsrt is run on a filesystem that doesn't have a rt volume, it's
possible to change the rt extent size.  If the root directory was
previously set up with an inherited extent size hint and rtinherit, it's
possible that the hint is no longer a multiple of the rt extent size.
Although the verifiers don't complain about this, xfs_repair will, so if
we detect this situation, log the root directory to clean it up.  This
is still racy, but it's better than nothing.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>

fs/xfs/xfs_rtalloc.c

@@ -784,6 +784,39 @@ xfs_alloc_rsum_cache(
 		xfs_warn(mp, "could not allocate realtime summary cache");
 }
 
+/*
+ * If we changed the rt extent size (meaning there was no rt volume previously)
+ * and the root directory had EXTSZINHERIT and RTINHERIT set, it's possible
+ * that the extent size hint on the root directory is no longer congruent with
+ * the new rt extent size.  Log the rootdir inode to fix this.
+ */
+static int
+xfs_growfs_rt_fixup_extsize(
+	struct xfs_mount	*mp)
+{
+	struct xfs_inode	*ip = mp->m_rootip;
+	struct xfs_trans	*tp;
+	int			error = 0;
+
+	xfs_ilock(ip, XFS_IOLOCK_EXCL);
+	if (!(ip->i_diflags & XFS_DIFLAG_RTINHERIT) ||
+	    !(ip->i_diflags & XFS_DIFLAG_EXTSZINHERIT))
+		goto out_iolock;
+
+	error = xfs_trans_alloc_inode(ip, &M_RES(mp)->tr_ichange, 0, 0, false,
+			&tp);
+	if (error)
+		goto out_iolock;
+
+	xfs_trans_log_inode(tp, ip, XFS_ILOG_CORE);
+	error = xfs_trans_commit(tp);
+	xfs_iunlock(ip, XFS_ILOCK_EXCL);
+
+out_iolock:
+	xfs_iunlock(ip, XFS_IOLOCK_EXCL);
+	return error;
+}
+
 /*
  * Visible (exported) functions.
  */
@@ -812,6 +845,7 @@ xfs_growfs_rt(
 	xfs_extlen_t	rsumblocks;	/* current number of rt summary blks */
 	xfs_sb_t	*sbp;		/* old superblock */
 	uint8_t		*rsum_cache;	/* old summary cache */
+	xfs_agblock_t	old_rextsize = mp->m_sb.sb_rextsize;
 
 	sbp = &mp->m_sb;
 
@@ -1046,6 +1080,12 @@ xfs_growfs_rt(
 	if (error)
 		goto out_free;
 
+	if (old_rextsize != in->extsize) {
+		error = xfs_growfs_rt_fixup_extsize(mp);
+		if (error)
+			goto out_free;
+	}
+
 	/* Update secondary superblocks now the physical grow has completed */
 	error = xfs_update_secondary_sbs(mp);