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.

mysql-test/include/handler.inc

@@ -692,3 +692,29 @@ unlock tables;
 drop table t1;
 --error ER_UNKNOWN_TABLE
 handler t1 read a next;
+
+#
+# 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
+#
+
+--disable_warnings
+drop table if exists t1;
+--enable_warnings
+create table t1 (a int);
+insert into t1 values (1);
+handler t1 open;
+connect(con1,localhost,root,,);
+send alter table t1 engine=memory;
+connection default;
+let $wait_condition=
+  select count(*) = 1 from information_schema.processlist
+  where state = "rename result table" and info = "alter table t1 engine=memory";
+--source include/wait_condition.inc
+--error ER_ILLEGAL_HA
+handler t1 read a next;
+handler t1 close;
+connection con1;
+--reap
+drop table t1;
+connection default;

mysql-test/r/handler_innodb.result

@@ -730,3 +730,12 @@ 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;

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;

sql/sql_handler.cc

@@ -160,6 +160,9 @@ static void mysql_ha_close_table(THD *thd, TABLE_LIST *tables,
     table->query_id= thd->query_id;
     table->open_by_handler= 0;
   }
+
+  /* Mark table as closed, ready for re-open if necessary. */
+  tables->table= NULL;
 }
 
 /*
@@ -177,8 +180,7 @@ static void mysql_ha_close_table(THD *thd, TABLE_LIST *tables,
     'reopen' is set when a handler table is to be re-opened. In this case,
     'tables' is the pointer to the hashed TABLE_LIST object which has been
     saved on the original open.
-    'reopen' is also used to suppress the sending of an 'ok' message or
-    error messages.
+    'reopen' is also used to suppress the sending of an 'ok' message.
 
   RETURN
     FALSE OK
@@ -214,7 +216,6 @@ bool mysql_ha_open(THD *thd, TABLE_LIST *tables, bool reopen)
                     strlen(tables->alias) + 1))
     {
       DBUG_PRINT("info",("duplicate '%s'", tables->alias));
-      if (! reopen)
       my_error(ER_NONUNIQ_TABLE, MYF(0), tables->alias);
       goto err;
     }
@@ -259,7 +260,6 @@ bool mysql_ha_open(THD *thd, TABLE_LIST *tables, bool reopen)
   /* There can be only one table in '*tables'. */
   if (! (tables->table->file->ha_table_flags() & HA_CAN_SQL_HANDLER))
   {
-    if (! reopen)
     my_error(ER_ILLEGAL_HA, MYF(0), tables->alias);
     goto err;
   }
@@ -479,8 +479,7 @@ retry:
 
   if (need_reopen)
   {
-    mysql_ha_close_table(thd, tables, FALSE);
-    hash_tables->table= NULL;
+    mysql_ha_close_table(thd, hash_tables, FALSE);
     /*
       The lock might have been aborted, we need to manually reset
       thd->some_tables_deleted because handler's tables are closed
@@ -761,11 +760,7 @@ void mysql_ha_flush(THD *thd)
   {
     hash_tables= (TABLE_LIST*) hash_element(&thd->handler_tables_hash, i);
     if (hash_tables->table && hash_tables->table->needs_reopen_or_name_lock())
-    {
       mysql_ha_close_table(thd, hash_tables, TRUE);
-      /* Mark table as closed, ready for re-open. */
-      hash_tables->table= NULL;
-    }
   }
 
   DBUG_VOID_RETURN;