MDEV-6728 KILL QUERY executed on an idle connection can interrupt the next query

reset KILL_QUERY when a new query execution is just about to be started

mysql-test/r/kill_processlist-6619.result

@@ -3,10 +3,12 @@ SHOW PROCESSLIST;
 Id	User	Host	db	Command	Time	State	Info	Progress
 #	root	#	test	Sleep	#	#	NULL	0.000
 #	root	#	test	Query	#	#	SHOW PROCESSLIST	0.000
+SET DEBUG_SYNC='before_execute_sql_command WAIT_FOR go';
+SHOW PROCESSLIST;
 connection default;
 KILL QUERY con_id;
+SET DEBUG_SYNC='now SIGNAL go';
 connection con1;
-SHOW PROCESSLIST;
 ERROR 70100: Query execution was interrupted
 SHOW PROCESSLIST;
 Id	User	Host	db	Command	Time	State	Info	Progress

mysql-test/r/kill_query-6728.result

+connect  con1,localhost,root,,;
+connection default;
+kill query id;
+connection con1;
+select count(*) > 0 from mysql.user;
+count(*) > 0
+1

mysql-test/r/show_check.result

@@ -1456,12 +1456,6 @@ GRANT PROCESS ON *.* TO test_u@localhost;
 SHOW ENGINE MYISAM MUTEX;
 SHOW ENGINE MYISAM STATUS;
 DROP USER test_u@localhost;
-#
-# Bug #48985: show create table crashes if previous access to the table
-#    was killed
-#
-SHOW CREATE TABLE non_existent;
-ERROR 70100: Query execution was interrupted
 End of 5.1 tests
 #
 # Bug#52593 SHOW CREATE TABLE is blocked if table is locked

mysql-test/t/kill_processlist-6619.test

@@ -2,16 +2,21 @@
 # MDEV-6619 SHOW PROCESSLIST returns empty result set after KILL QUERY
 #
 --source include/not_embedded.inc
+--source include/have_debug_sync.inc
+
 --enable_connect_log
 --connect (con1,localhost,root,,)
 --let $con_id = `SELECT CONNECTION_ID()`
 --replace_column 1 # 3 # 6 # 7 #
 SHOW PROCESSLIST;
+SET DEBUG_SYNC='before_execute_sql_command WAIT_FOR go';
+send SHOW PROCESSLIST;
 --connection default
 --replace_result $con_id con_id
 eval KILL QUERY $con_id;
+SET DEBUG_SYNC='now SIGNAL go';
 --connection con1
 --error ER_QUERY_INTERRUPTED
-SHOW PROCESSLIST;
+reap;
 --replace_column 1 # 3 # 6 # 7 #
 SHOW PROCESSLIST;

mysql-test/t/kill_query-6728.test

+#
+# MDEV-6728 KILL QUERY executed on an idle connection can interrupt the next query
+#
+--enable_connect_log
+--connect (con1,localhost,root,,)
+let $id=`select connection_id()`;
+
+--connection default
+--replace_result $id id
+eval kill query $id;
+
+--connection con1
+select count(*) > 0 from mysql.user;
+

mysql-test/t/show_check.test

@@ -1210,33 +1210,8 @@ disconnect conn1;
 connection default;
 DROP USER test_u@localhost;
 
-
---echo #
---echo # Bug #48985: show create table crashes if previous access to the table
---echo #    was killed
---echo #
-
-connect(con1,localhost,root,,);
-CONNECTION con1;
-LET $ID= `SELECT connection_id()`;
-
-CONNECTION default;
---disable_query_log
-eval KILL QUERY $ID;
---enable_query_log
-
-CONNECTION con1;
---error ER_QUERY_INTERRUPTED
-SHOW CREATE TABLE non_existent;
-
-DISCONNECT con1;
---source include/wait_until_disconnected.inc
-CONNECTION default;
-
-
 --echo End of 5.1 tests
 
-
 --echo #
 --echo # Bug#52593 SHOW CREATE TABLE is blocked if table is locked
 --echo #           for write by another connection

mysql-test/t/sp_notembedded.test

@@ -374,6 +374,9 @@ CREATE VIEW v1 AS SELECT f1('a') FROM t1;
 --send SELECT * FROM v1
 
 --connection default
+let $wait_condition=
+  select count(*) = 2 from information_schema.processlist where state = "User sleep";
+--source include/wait_condition.inc
 --disable_query_log
 --eval KILL QUERY $ID_2
 --eval KILL QUERY $ID_1

sql/sql_class.h

@@ -3229,6 +3229,14 @@ public:
       mysql_mutex_unlock(&LOCK_thd_data);
     }
   }
+  inline void reset_kill_query()
+  {
+    if (killed < KILL_CONNECTION)
+    {
+      reset_killed();
+      mysys_var->abort= 0;
+    }
+  }
   inline void send_kill_message() const
   {
     int err= killed_errno();

sql/sql_parse.cc

@@ -1124,6 +1124,7 @@ bool dispatch_command(enum enum_server_command command, THD *thd,
   thd->enable_slow_log= TRUE;
   thd->query_plan_flags= QPLAN_INIT;
   thd->lex->sql_command= SQLCOM_END; /* to avoid confusing VIEW detectors */
+  thd->reset_kill_query();
 
   DEBUG_SYNC(thd,"dispatch_command_before_set_time");
 
@@ -5111,11 +5112,7 @@ finish:
         if (! thd->get_stmt_da()->is_set())
           thd->send_kill_message();
       }
-      if (thd->killed < KILL_CONNECTION)
-      {
-        thd->reset_killed();
-        thd->mysys_var->abort= 0;
-      }
+      thd->reset_kill_query();
     }
     if (thd->is_error() || (thd->variables.option_bits & OPTION_MASTER_SQL_ERROR))
       trans_rollback_stmt(thd);