Bug#41110: crash with handler command when used concurrently with alter table

Bug#41112: crash in mysql_ha_close_table/get_lock_data with alter table

The problem is that the server wasn't handling robustly failures
to re-open a table during a HANDLER .. READ statement. If the
table needed to be re-opened due to it's storage engine being
altered to one that doesn't support HANDLER, a reference (dangling
pointer) to a closed table could be left in place and accessed in
later attempts to fetch from the table using the handler. Also,
if the server failed to set a error message if the re-open
failed. These problems could lead to server crashes or hangs.

The solution is to remove any references to a closed table and
to set a error if reopening a table during a HANDLER .. READ
statement fails.

mysql-test/include/handler.inc:
  Add test case for Bug#41110 and Bug#41112
mysql-test/r/handler_innodb.result:
  Add test case result for Bug#41110 and Bug#41112
mysql-test/r/handler_myisam.result:
  Add test case result for Bug#41110 and Bug#41112
sql/sql_handler.cc:
  Remove redundant reopen check.
  Set errors even if reopening table.
  Reset TABLE_LIST::table reference when the table is closed.

1 files changed, 9 insertions, 0 deletions

diff --git a/mysql-test/r/handler_myisam.result b/mysql-test/r/handler_myisam.result
index 0b27b07c4d2..afbf2d9fb6d 100644
--- a/mysql-test/r/handler_myisam.result
+++ b/mysql-test/r/handler_myisam.result
@@ -728,3 +728,12 @@ unlock tables;
 drop table t1;
 handler t1 read a next;
 ERROR 42S02: Unknown table 't1' in HANDLER
+drop table if exists t1;
+create table t1 (a int);
+insert into t1 values (1);
+handler t1 open;
+alter table t1 engine=memory;
+handler t1 read a next;
+ERROR HY000: Table storage engine for 't1' doesn't have this option
+handler t1 close;
+drop table t1;