ITS#8311 fix page_split from update_key

Check for top of stack. Usually the cursor only has height 1 when
calling page_split, but not always.

libraries/liblmdb/mdb.c

@@ -6512,16 +6512,18 @@ fix_parent:
 			 * update branch key if there is a parent page
 			 */
 			if (mc->mc_top && !mc->mc_ki[mc->mc_top]) {
-				unsigned short top = mc->mc_top;
+				unsigned short dtop = 1;
 				mc->mc_top--;
 				/* slot 0 is always an empty key, find real slot */
-				while (mc->mc_top && !mc->mc_ki[mc->mc_top])
+				while (mc->mc_top && !mc->mc_ki[mc->mc_top]) {
 					mc->mc_top--;
+					dtop++;
+				}
 				if (mc->mc_ki[mc->mc_top])
 					rc2 = mdb_update_key(mc, key);
 				else
 					rc2 = MDB_SUCCESS;
-				mc->mc_top = top;
+				mc->mc_top += dtop;
 				if (rc2)
 					return rc2;
 			}
@@ -8370,12 +8372,14 @@ mdb_page_split(MDB_cursor *mc, MDB_val *newkey, MDB_val *newdata, pgno_t newpgno
 	rp->mp_pad = mp->mp_pad;
 	DPRINTF(("new right sibling: page %"Z"u", rp->mp_pgno));
 
-	if (mc->mc_snum < 2) {
+	if (mc->mc_top < 1) {
 		if ((rc = mdb_page_new(mc, P_BRANCH, 1, &pp)))
 			goto done;
 		/* shift current top to make room for new parent */
-		mc->mc_pg[1] = mc->mc_pg[0];
-		mc->mc_ki[1] = mc->mc_ki[0];
+		for (i=mc->mc_snum; i>0; i--) {
+			mc->mc_pg[i] = mc->mc_pg[i-1];
+			mc->mc_ki[i] = mc->mc_ki[i-1];
+		}
 		mc->mc_pg[0] = pp;
 		mc->mc_ki[0] = 0;
 		mc->mc_db->md_root = pp->mp_pgno;
@@ -8391,8 +8395,8 @@ mdb_page_split(MDB_cursor *mc, MDB_val *newkey, MDB_val *newdata, pgno_t newpgno
 			mc->mc_db->md_depth--;
 			goto done;
 		}
-		mc->mc_snum = 2;
-		mc->mc_top = 1;
+		mc->mc_snum++;
+		mc->mc_top++;
 		ptop = 0;
 	} else {
 		ptop = mc->mc_top-1;