MDEV-17196 Crash during instant ADD COLUMN with long DEFAULT value

A debug assertion would fail if an instant ADD COLUMN operation
involves splitting the leftmost leaf page and storing a default
value off-page. Another debug assertion could fail if the
default value does not fit in an undo log page.

btr_cur_pessimistic_update(): Invoke rec_offs_make_valid()
in order to prevent rec_offs_validate() assertion failure.

innobase_add_instant_try(): Invoke btr_cur_pessimistic_update()
with the BTR_KEEP_POS_FLAG, which is the correct course of action
when BLOBs may need to be written. Whenever returning true,
ensure that my_error() will have been called.

mysql-test/suite/innodb/r/instant_alter.result

@@ -464,6 +464,12 @@ ALGORITHM=INSTANT;
 SET foreign_key_checks=1;
 ALTER TABLE t2 COMMENT 'domestic keys only', DROP FOREIGN KEY fk;
 ALTER TABLE t1 DROP FOREIGN KEY t1_ibfk_1;
+ALTER TABLE t1 ADD COLUMN big BLOB NOT NULL
+DEFAULT REPEAT('a', @@GLOBAL.innodb_page_size * .75);
+CHECK TABLE t2, t1;
+Table	Op	Msg_type	Msg_text
+test.t2	check	status	OK
+test.t1	check	status	OK
 DROP TABLE t2, t1;
 CREATE TABLE t1
 (id INT PRIMARY KEY, c2 INT UNIQUE,
@@ -875,6 +881,12 @@ ALGORITHM=INSTANT;
 SET foreign_key_checks=1;
 ALTER TABLE t2 COMMENT 'domestic keys only', DROP FOREIGN KEY fk;
 ALTER TABLE t1 DROP FOREIGN KEY t1_ibfk_1;
+ALTER TABLE t1 ADD COLUMN big BLOB NOT NULL
+DEFAULT REPEAT('a', @@GLOBAL.innodb_page_size * .75);
+CHECK TABLE t2, t1;
+Table	Op	Msg_type	Msg_text
+test.t2	check	status	OK
+test.t1	check	status	OK
 DROP TABLE t2, t1;
 CREATE TABLE t1
 (id INT PRIMARY KEY, c2 INT UNIQUE,
@@ -1286,11 +1298,17 @@ ALGORITHM=INSTANT;
 SET foreign_key_checks=1;
 ALTER TABLE t2 COMMENT 'domestic keys only', DROP FOREIGN KEY fk;
 ALTER TABLE t1 DROP FOREIGN KEY t1_ibfk_1;
+ALTER TABLE t1 ADD COLUMN big BLOB NOT NULL
+DEFAULT REPEAT('a', @@GLOBAL.innodb_page_size * .75);
+CHECK TABLE t2, t1;
+Table	Op	Msg_type	Msg_text
+test.t2	check	status	OK
+test.t1	check	status	OK
 DROP TABLE t2, t1;
 disconnect analyze;
 SELECT variable_value-@old_instant instants
 FROM information_schema.global_status
 WHERE variable_name = 'innodb_instant_alter_column';
 instants
-45
+48
 SET GLOBAL innodb_purge_rseg_truncate_frequency= @saved_frequency;

mysql-test/suite/innodb/t/instant_alter.test

@@ -338,6 +338,9 @@ ALGORITHM=INSTANT;
 SET foreign_key_checks=1;
 ALTER TABLE t2 COMMENT 'domestic keys only', DROP FOREIGN KEY fk;
 ALTER TABLE t1 DROP FOREIGN KEY t1_ibfk_1;
+ALTER TABLE t1 ADD COLUMN big BLOB NOT NULL
+DEFAULT REPEAT('a', @@GLOBAL.innodb_page_size * .75);
+CHECK TABLE t2, t1;
 DROP TABLE t2, t1;
 
 dec $format;

storage/innobase/btr/btr0cur.cc

@@ -4764,6 +4764,7 @@ btr_cur_pessimistic_update(
 			know the size of the freed record. */
 			btr_page_reorganize(page_cursor, index, mtr);
 			rec = page_cursor->rec;
+			rec_offs_make_valid(rec, index, true, *offsets);
 		} else if (!dict_table_is_locking_disabled(index->table)) {
 			lock_rec_restore_from_page_infimum(
 				btr_cur_get_block(cursor), rec, block);

storage/innobase/handler/handler0alter.cc

@@ -4379,6 +4379,7 @@ innobase_add_instant_try(
 	que_thr_t* thr = pars_complete_graph_for_exec(
 		NULL, trx, ctx->heap, NULL);
 
+	dberr_t err;
 	if (rec_is_default_row(rec, index)) {
 		ut_ad(page_rec_is_user_rec(rec));
 		if (!page_has_next(block->frame)
@@ -4403,14 +4404,15 @@ innobase_add_instant_try(
 		ulint* offsets = NULL;
 		mem_heap_t* offsets_heap = NULL;
 		big_rec_t* big_rec;
-		dberr_t error = btr_cur_pessimistic_update(
-			BTR_NO_LOCKING_FLAG, btr_pcur_get_btr_cur(&pcur),
+		err = btr_cur_pessimistic_update(
+			BTR_NO_LOCKING_FLAG | BTR_KEEP_POS_FLAG,
+			btr_pcur_get_btr_cur(&pcur),
 			&offsets, &offsets_heap, ctx->heap,
 			&big_rec, update, UPD_NODE_NO_ORD_CHANGE,
 			thr, trx->id, &mtr);
 		if (big_rec) {
-			if (error == DB_SUCCESS) {
-				error = btr_store_big_rec_extern_fields(
+			if (err == DB_SUCCESS) {
+				err = btr_store_big_rec_extern_fields(
 					&pcur, offsets, big_rec, &mtr,
 					BTR_STORE_UPDATE);
 			}
@@ -4421,8 +4423,7 @@ innobase_add_instant_try(
 			mem_heap_free(offsets_heap);
 		}
 		btr_pcur_close(&pcur);
-		mtr.commit();
-		return error != DB_SUCCESS;
+		goto func_exit;
 	} else if (page_rec_is_supremum(rec)) {
 empty_table:
 		/* The table is empty. */
@@ -4438,7 +4439,6 @@ innobase_add_instant_try(
 	mtr.commit();
 	mtr.start();
 	index->set_modified(mtr);
-	dberr_t err;
 	if (page_t* root = btr_root_get(index, &mtr)) {
 		switch (fil_page_get_type(root)) {
 		case FIL_PAGE_TYPE_INSTANT:
@@ -4451,8 +4451,7 @@ innobase_add_instant_try(
 			break;
 		default:
 			DBUG_ASSERT(!"wrong page type");
-			mtr.commit();
-			return true;
+			goto func_exit;
 		}
 
 		mlog_write_ulint(root + FIL_PAGE_TYPE,
@@ -4469,8 +4468,16 @@ innobase_add_instant_try(
 		err = DB_CORRUPTION;
 	}
 
+func_exit:
 	mtr.commit();
-	return err != DB_SUCCESS;
+
+	if (err != DB_SUCCESS) {
+		my_error_innodb(err, table->s->table_name.str,
+				user_table->flags);
+		return true;
+	}
+
+	return false;
 }
 
 /** Update INNODB SYS_COLUMNS on new virtual column's position