Fix for bug #26380: LOCK TABLES + FLUSH LOGS causes deadlock

The log tables are by nature PERFORMANCE_SCHEMA tables,
which should not be affected by SET GLOBAL READ_ONLY or FLUSH TABLES
WITH READ LOCK.

The implementation of FLUSH TABLES WITH READ LOCK already ignored log tables.
Now with this patch, the implementation of LOCK TABLE also ignore a
global read lock for log tables, which was the missing symmetry.


mysql-test/r/flush.result:
  Fix for bug #26380: LOCK TABLES + FLUSH LOGS causes deadlock
    - test result.
mysql-test/t/flush.test:
  Fix for bug #26380: LOCK TABLES + FLUSH LOGS causes deadlock
    - test case.
sql/lock.cc:
  Fix for bug #26380: LOCK TABLES + FLUSH LOGS causes deadlock
    - logger.is_privileged_thread() used.
sql/log.h:
  Fix for bug #26380: LOCK TABLES + FLUSH LOGS causes deadlock
    - LOGGER::is_privileged_thread() introduced that returns TRUE if a given thread 
      is either a general_log or a slow_log or a privileged thread.
sql/sql_base.cc:
  Fix for bug #26380: LOCK TABLES + FLUSH LOGS causes deadlock
    - pass MYSQL_LOCK_IGNORE_GLOBAL_READ_LOCK to the mysql_lock_tables() in case of 
      call from a logger in order not to honor the GLOBAL READ LOCK 
      and to avoid possible deadlocks.

1 files changed, 1 insertions, 3 deletions

diff --git a/sql/lock.cc b/sql/lock.cc
index 6f1dd0669ee..9785bc4ac00 100644
--- a/sql/lock.cc
+++ b/sql/lock.cc
@@ -707,9 +707,7 @@ static MYSQL_LOCK *get_lock_data(THD *thd, TABLE **table_ptr, uint count,
     if (!table_ptr[i]-> file->
           check_if_locking_is_allowed(thd->lex->sql_command, thd->lex->type,
                                       table_ptr[i], count, i, &system_count,
-                                      (thd == logger.get_general_log_thd()) ||
-                                      (thd == logger.get_slow_log_thd()) ||
-                                      (thd == logger.get_privileged_thread())))
+                                      logger.is_privileged_thread(thd)))
       DBUG_RETURN(0);
   }