MDEV-14080 InnoDB shutdown sometimes hangs

srv_purge_wakeup(): If thd_destructor_proxy has initiated the first
step of shutdown, ensure that all purge threads terminate.

logs_empty_and_mark_files_at_shutdown(): Add a debug assertion.
(The purge threads should have been shut down already before this step.)

storage/innobase/log/log0log.cc

@@ -1979,6 +1979,7 @@ logs_empty_and_mark_files_at_shutdown(void)
 		goto wait_suspend_loop;
 	case SRV_PURGE:
 	case SRV_WORKER:
+		ut_ad(!"purge was not shut down");
 		srv_purge_wakeup();
 		thread_name = "purge thread";
 		goto wait_suspend_loop;

storage/innobase/srv/srv0srv.cc

@@ -2980,8 +2980,11 @@ srv_purge_wakeup()
 {
 	ut_ad(!srv_read_only_mode);
 
-	if (srv_force_recovery < SRV_FORCE_NO_BACKGROUND) {
+	if (srv_force_recovery >= SRV_FORCE_NO_BACKGROUND) {
+		return;
+	}
 
+	do {
 		srv_release_threads(SRV_PURGE, 1);
 
 		if (srv_n_purge_threads > 1) {
@@ -2989,7 +2992,9 @@ srv_purge_wakeup()
 
 			srv_release_threads(SRV_WORKER, n_workers);
 		}
-	}
+	} while (!srv_running
+		 && (srv_sys.n_threads_active[SRV_WORKER]
+		     || srv_sys.n_threads_active[SRV_PURGE]));
 }
 
 /** Check if tablespace is being truncated.