Assertion "!n_mysql_tables_in_use" failed in trx_t::free after ALTER

--source include/have_innodb.inc

--source include/have_debug.inc

create table t1 (a int, b int)engine=innodb;

SET @saved_dbug = @@SESSION.debug_dbug;

SET debug_dbug='+d,external_lock_failure';

--error ER_GET_ERRMSG

alter table t1 add column c int;

SET debug_dbug= @saved_dbug;

drop table t1;

#3  <signal handler called>

#4  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50

#5  0x00007f7e20100859 in __GI_abort () at abort.c:79

#6  0x00007f7e20100729 in __assert_fail_base (fmt=0x7f7e20296588 "%s%s%s:%u: %s%sAssertion `%s' failed.\n%n", assertion=0x56146dac07a0 "!n_mysql_tables_in_use", file=0x56146dac0040 "/10.6/src/storage/innobase/trx/trx0trx.cc", line=373, function=<optimized out>) at assert.c:94

#7  0x00007f7e20111fd6 in __GI___assert_fail (assertion=0x56146dac07a0 "!n_mysql_tables_in_use", file=0x56146dac0040 "/10.6/src/storage/innobase/trx/trx0trx.cc", line=373, function=0x56146dac07e0 "void trx_t::free()") at assert.c:103

#8  0x000056146c458b38 in trx_t::free (this=0x7f7e161af3c0) at /10.6/src/storage/innobase/trx/trx0trx.cc:373

#9  0x000056146be250c2 in innobase_close_connection (thd=0x62c000110288) at /10.6/src/storage/innobase/handler/ha_innodb.cc:2987

#10 0x000056146b3638a8 in ha_close_connection (thd=0x62c000110288) at /10.6/src/sql/handler.cc:923

#11 0x000056146a9467d9 in THD::free_connection (this=0x62c000110288) at /10.6/src/sql/sql_class.cc:1705

#12 0x000056146a740862 in unlink_thd (thd=0x62c000110288) at /10.6/src/sql/mysqld.cc:2746

#13 0x000056146af1b744 in do_handle_one_connection (connect=0x611000032708, put_in_cache=true) at /10.6/src/sql/sql_connect.cc:1397

#14 0x000056146af1b1ea in handle_one_connection (arg=0x6110000325c8) at /10.6/src/sql/sql_connect.cc:1298

#15 0x000056146bbf9608 in pfs_spawn_thread (arg=0x618000005d08) at /10.6/src/storage/perfschema/pfs.cc:2201

#16 0x00007f7e206c2609 in start_thread (arg=<optimized out>) at pthread_create.c:477

#17 0x00007f7e201fd353 in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95