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, 6 insertions, 0 deletions

diff --git a/sql/log.h b/sql/log.h
index 25bcbd6c62d..d92e0117bcc 100644
--- a/sql/log.h
+++ b/sql/log.h
@@ -600,6 +600,12 @@ public:
     else
       return NULL;
   }
+  bool is_privileged_thread(THD *thd)
+  {
+    return thd == get_general_log_thd() ||
+           thd == get_slow_log_thd() ||
+           thd == get_privileged_thread();
+  }
 };
 
 enum enum_binlog_format {