xfs: use the actual AG length when reserving blocks

We need to use the actual AG length when making per-AG reservations,
since we could otherwise end up reserving more blocks out of the last
AG than there are actual blocks.

Complained-about-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
index 93d12fa..242e809 100644
--- a/fs/xfs/xfs_fsops.c
+++ b/fs/xfs/xfs_fsops.c
@@ -631,6 +631,20 @@
 	xfs_set_low_space_thresholds(mp);
 	mp->m_alloc_set_aside = xfs_alloc_set_aside(mp);
 
+	/*
+	 * If we expanded the last AG, free the per-AG reservation
+	 * so we can reinitialize it with the new size.
+	 */
+	if (new) {
+		struct xfs_perag	*pag;
+
+		pag = xfs_perag_get(mp, agno);
+		error = xfs_ag_resv_free(pag);
+		xfs_perag_put(pag);
+		if (error)
+			goto out;
+	}
+
 	/* Reserve AG metadata blocks. */
 	error = xfs_fs_reserve_ag_blocks(mp);
 	if (error && error != -ENOSPC)