Add RelationOpenSmgr() calls to ensure rd_smgr is valid when we try to

use it.  While it normally has been opened earlier during btree index
build, testing shows that it's possible for the link to be closed again
if an sinval reset occurs while the index is being built.

src/backend/access/nbtree/nbtsort.c

@@ -56,7 +56,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtsort.c,v 1.96 2005/11/22 18:17:06 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtsort.c,v 1.97 2006/01/07 22:45:41 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -271,6 +271,9 @@ _bt_blnewpage(uint32 level)
 static void
 _bt_blwritepage(BTWriteState *wstate, Page page, BlockNumber blkno)
 {
+	/* Ensure rd_smgr is open (could have been closed by relcache flush!) */
+	RelationOpenSmgr(wstate->index);
+
 	/* XLOG stuff */
 	if (wstate->btws_use_wal)
 	{
@@ -818,5 +821,8 @@ _bt_load(BTWriteState *wstate, BTSpool *btspool, BTSpool *btspool2)
 	 * occurs.
 	 */
 	if (!wstate->index->rd_istemp)
+	{
+		RelationOpenSmgr(wstate->index);
 		smgrimmedsync(wstate->index->rd_smgr);
+	}
 }