[PATCH 6.6 020/140] xfs: error out when a superblock buffer update reduces the agcount

6.6-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Christoph Hellwig <[email protected]>

commit b882b0f8138ffa935834e775953f1630f89bbb62 upstream.

XFS currently does not support reducing the agcount, so error out if
a logged sb buffer tries to shrink the agcount.

Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Brian Foster <[email protected]>
Reviewed-by: Darrick J. Wong <[email protected]>
Signed-off-by: Carlos Maiolino <[email protected]>
Signed-off-by: Catherine Hoang <[email protected]>
Acked-by: Darrick J. Wong <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
 fs/xfs/xfs_buf_item_recover.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/fs/xfs/xfs_buf_item_recover.c
+++ b/fs/xfs/xfs_buf_item_recover.c
@@ -713,6 +713,11 @@ xlog_recover_do_primary_sb_buffer(
 	 */
 	xfs_sb_from_disk(&mp->m_sb, dsb);
 
+	if (mp->m_sb.sb_agcount < orig_agcount) {
+		xfs_alert(mp, "Shrinking AG count in log recovery not supported");
+		return -EFSCORRUPTED;
+	}
+
 	/*
 	 * Initialize the new perags, and also update various block and inode
 	 * allocator setting based off the number of AGs or total blocks.