BUG#12574820: binlog.binlog_tmp_table timing out in daily and weekly trunk run

Problem: MYSQL_BIN_LOG::reset_logs acquires mutexes in wrong order.
The correct order is first LOCK_thread_count and then LOCK_log. This function
does it the other way around. This leads to deadlock when run in parallel
with a thread that takes the two locks in correct order. For example, a thread
that disconnects will take the locks in the correct order.
Fix: change order of the locks in MYSQL_BIN_LOG::reset_logs:
first LOCK_thread_count and then LOCK_log.

mysql-test/suite/binlog/r/binlog_reset_master.result

+RESET MASTER;

mysql-test/suite/binlog/t/binlog_reset_master.test

+# ==== Purpose ====
+#
+# Test bugs in RESET MASTER.
+
+--source include/have_debug.inc
+--source include/have_log_bin.inc
+
+#######################################################################
+# BUG#12574820: binlog.binlog_tmp_table timing out in daily and weekly trunk run
+# Problem: MYSQL_BIN_LOG::reset_logs acquired LOCK_thread_count and
+# LOCK_log in the wrong order. This could cause a deadlock when
+# RESET MASTER was run concurrently with a disconnecting thread.
+#######################################################################
+
+# We use sleep, not debug_sync, because the sync point needs to be in
+# the thread shut down code after the debug sync facility has been
+# shut down.
+--let $write_var= SET DEBUG="+d,sleep_after_lock_thread_count_before_delete_thd"; CREATE TEMPORARY TABLE test.t1 (a INT);
+--let $write_to_file= GENERATE
+--disable_query_log
+--source include/write_var_to_file.inc
+--enable_query_log
+
+--exec $MYSQL < $write_to_file
+RESET MASTER;
+--remove_file $write_to_file

sql/log.cc

@@ -2989,12 +2989,6 @@ bool MYSQL_BIN_LOG::reset_logs(THD* thd)
   DBUG_ENTER("reset_logs");
 
   ha_reset_logs(thd);
-  /*
-    We need to get both locks to be sure that no one is trying to
-    write to the index log file.
-  */
-  pthread_mutex_lock(&LOCK_log);
-  pthread_mutex_lock(&LOCK_index);
 
   /*
     The following mutex is needed to ensure that no threads call
@@ -3002,7 +2996,14 @@ bool MYSQL_BIN_LOG::reset_logs(THD* thd)
     thread. If the transaction involved MyISAM tables, it should go
     into binlog even on rollback.
   */
-  VOID(pthread_mutex_lock(&LOCK_thread_count));
+  pthread_mutex_lock(&LOCK_thread_count);
+
+  /*
+    We need to get both locks to be sure that no one is trying to
+    write to the index log file.
+  */
+  pthread_mutex_lock(&LOCK_log);
+  pthread_mutex_lock(&LOCK_index);
 
   /* Save variables so that we can reopen the log */
   save_name=name;

sql/mysqld.cc

@@ -1903,6 +1903,12 @@ void unlink_thd(THD *thd)
   pthread_mutex_unlock(&LOCK_connection_count);
 
   (void) pthread_mutex_lock(&LOCK_thread_count);
+  /*
+    Used by binlog_reset_master.  It would be cleaner to use
+    DEBUG_SYNC here, but that's not possible because the THD's debug
+    sync feature has been shut down at this point.
+  */
+  DBUG_EXECUTE_IF("sleep_after_lock_thread_count_before_delete_thd", sleep(5););
   thread_count--;
   delete thd;
   DBUG_VOID_RETURN;