Fix Bug #20139 Infinite loop after "FLUSH" and "LOCK tabX, general_log"

Due to incorrect handling of FLUSH TABLES, log tables were marked for flush,
but not reopened. Later we started to wait for the log table to be closed
(disabled) after the flush. And as nobody disabled logs in concurrent treads,
the command lasted forever.
After internal consultations it was decided to skip logs during FLUSH TABLES.
The reasoning is that logging is done in the "log device", whatever it is
which is always active and controlled by FLUSH LOGS. So, to flush logs
one should use FLUSH LOGS, and not FLUSH TABLES.


mysql-test/r/log_tables.result:
  update result file
mysql-test/t/log_tables.test:
  add a test for the bug
sql/sql_base.cc:
  Skip log tables during FLUSH TABLES

1 files changed, 5 insertions, 0 deletions

diff --git a/mysql-test/r/log_tables.result b/mysql-test/r/log_tables.result
index c61dd2247ee..c817c2752a0 100644
--- a/mysql-test/r/log_tables.result
+++ b/mysql-test/r/log_tables.result
@@ -72,3 +72,8 @@ sleep(2)
 select * from mysql.slow_log;
 start_time	user_host	query_time	lock_time	rows_sent	rows_examined	db	last_insert_id	insert_id	server_id	sql_text
 TIMESTAMP	USER_HOST	QUERY_TIME	00:00:00	1	0	test	0	0	1	select sleep(2)
+flush tables with read lock;
+unlock tables;
+use mysql;
+lock tables general_log read local, help_category read local;
+unlock tables;