fix InnoDB data race

srv_last_monitor_time: make all accesses relaxed atomical

WARNING: ThreadSanitizer: data race (pid=29031)
  Write of size 8 at 0x0000039e48e0 by thread T15:
    #0 srv_monitor_thread storage/innobase/srv/srv0srv.cc:1699:24 (mysqld+0x21a254e)

  Previous write of size 8 at 0x0000039e48e0 by thread T14:
    #0 srv_refresh_innodb_monitor_stats() storage/innobase/srv/srv0srv.cc:1165:24 (mysqld+0x21a3124)
    #1 srv_error_monitor_thread storage/innobase/srv/srv0srv.cc:1836:3 (mysqld+0x21a2d40)

  Location is global 'srv_last_monitor_time' of size 8 at 0x0000039e48e0 (mysqld+0x0000039e48e0)

  Thread T15 (tid=29050, running) created by main thread at:
    #0 pthread_create /home/kevg/fun/cpp_projects/llvm_toolchain/llvm/projects/compiler-rt/lib/tsan/rtl/tsan_interceptors.cc:992 (mysqld+0xb90016)
    #1 os_thread_create_func(void* (*)(void*), void*, unsigned long*) storage/innobase/os/os0thread.cc:137:12 (mysqld+0x1f50025)
    #2 innobase_start_or_create_for_mysql() storage/innobase/srv/srv0start.cc:2583:46 (mysqld+0x21b50b7)
    #3 innobase_init(void*) storage/innobase/handler/ha_innodb.cc:4193:8 (mysqld+0x1a5e3d7)
    #4 ha_initialize_handlerton(st_plugin_int*) sql/handler.cc:522:31 (mysqld+0xc74d33)
    #5 plugin_initialize(st_mem_root*, st_plugin_int*, int*, char**, bool) sql/sql_plugin.cc:1447:9 (mysqld+0x1376d5d)
    #6 plugin_init(int*, char**, int) sql/sql_plugin.cc:1729:15 (mysqld+0x13761c0)
    #7 init_server_components() sql/mysqld.cc:5348:7 (mysqld+0xc0d0ff)
    #8 mysqld_main(int, char**) sql/mysqld.cc:5943:7 (mysqld+0xc06f9d)
    #9 main sql/main.cc:25:10 (mysqld+0xbff71b)

Author: kevgs

storage/innobase/srv/srv0srv.cc

@@ -1162,7 +1162,8 @@ srv_refresh_innodb_monitor_stats(void)
 {
 	mutex_enter(&srv_innodb_monitor_mutex);
 
-	srv_last_monitor_time = time(NULL);
+	my_atomic_store32_explicit(&srv_last_monitor_time, time(NULL),
+				   MY_MEMORY_ORDER_RELAXED);
 
 	os_aio_refresh_stats();
 
@@ -1216,10 +1217,14 @@ srv_printf_innodb_monitor(
 	by zero if two users happen to call SHOW ENGINE INNODB STATUS at the
 	same time */
 
-	time_elapsed = difftime(current_time, srv_last_monitor_time)
+	time_elapsed =
+		difftime(current_time,
+			 my_atomic_load32_explicit(&srv_last_monitor_time,
+						   MY_MEMORY_ORDER_RELAXED))
 		+ 0.001;
 
-	srv_last_monitor_time = time(NULL);
+	my_atomic_store32_explicit(&srv_last_monitor_time, time(NULL),
+				   MY_MEMORY_ORDER_RELAXED);
 
 	fputs("\n=====================================\n", file);
 
@@ -1696,7 +1701,8 @@ DECLARE_THREAD(srv_monitor_thread)(void*)
 	pfs_register_thread(srv_monitor_thread_key);
 #endif /* UNIV_PFS_THREAD */
 
-	srv_last_monitor_time = ut_time();
+	my_atomic_store32_explicit(&srv_last_monitor_time, ut_time(),
+				   MY_MEMORY_ORDER_RELAXED);
 	last_monitor_time = ut_time();
 	mutex_skipped = 0;
 	last_srv_print_monitor = srv_print_innodb_monitor;
@@ -1829,7 +1835,10 @@ DECLARE_THREAD(srv_error_monitor_thread)(void*)
 		old_lsn = new_lsn;
 	}
 
-	if (difftime(time(NULL), srv_last_monitor_time) > 60) {
+	if (difftime(time(NULL),
+		     my_atomic_load32_explicit(&srv_last_monitor_time,
+					       MY_MEMORY_ORDER_RELAXED))
+	    > 60) {
 		/* We referesh InnoDB Monitor values so that averages are
 		printed from at most 60 last seconds */