Prevent interleaved error log output on InnoDB startup

buf_flush_page_cleaner_coordinator(): Signal the thread creator
that the error log output regarding setpriority() has been issued.

innobase_start_or_create_for_mysql(): Wait for
buf_flush_page_cleaner_coordinator() to completely start up.

This prevents sporadic failures of tests that search the server
error log for InnoDB redo log recovery messages.

storage/innobase/buf/buf0flu.cc

@@ -3133,12 +3133,6 @@ DECLARE_THREAD(buf_flush_page_cleaner_coordinator)(
 			os_thread_create */
 {
 	my_thread_init();
-	ulint	next_loop_time = ut_time_ms() + 1000;
-	ulint	n_flushed = 0;
-	ulint	last_activity = srv_get_activity_count();
-	ulint	last_pages = 0;
-
-	my_thread_init();
 #ifdef UNIV_PFS_THREAD
 	pfs_register_thread(page_cleaner_thread_key);
 #endif /* UNIV_PFS_THREAD */
@@ -3160,6 +3154,8 @@ DECLARE_THREAD(buf_flush_page_cleaner_coordinator)(
 		" page cleaner thread priority can be changed."
 		" See the man page of setpriority().";
 	}
+	/* Signal that setpriority() has been attempted. */
+	os_event_set(recv_sys->flush_end);
 #endif /* UNIV_LINUX */
 
 	while (!srv_read_only_mode
@@ -3209,6 +3205,10 @@ DECLARE_THREAD(buf_flush_page_cleaner_coordinator)(
 	ulint	warn_interval = 1;
 	ulint	warn_count = 0;
 	int64_t	sig_count = os_event_reset(buf_flush_event);
+	ulint	next_loop_time = ut_time_ms() + 1000;
+	ulint	n_flushed = 0;
+	ulint	last_activity = srv_get_activity_count();
+	ulint	last_pages = 0;
 
 	while (srv_shutdown_state == SRV_SHUTDOWN_NONE) {
 

storage/innobase/srv/srv0start.cc

@@ -1861,6 +1861,10 @@ innobase_start_or_create_for_mysql()
 					 NULL, NULL);
 		}
 
+#ifdef UNIV_LINUX
+		/* Wait for the setpriority() call to finish. */
+		os_event_wait(recv_sys->flush_end);
+#endif /* UNIV_LINUX */
 		srv_start_state_set(SRV_START_STATE_IO);
 	}