From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f194.google.com ([209.85.128.194]:33188 "EHLO mail-wr0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S967843AbeBOMCd (ORCPT ); Thu, 15 Feb 2018 07:02:33 -0500 From: Ulrich Hecht To: linux-renesas-soc@vger.kernel.org, linux-serial@vger.kernel.org Cc: wsa@the-dreams.de, geert@linux-m68k.org, yoshihiro.shimoda.uh@renesas.com, Ulrich Hecht Subject: [PATCH] serial: sh-sci: prevent lockup on full TTY buffers Date: Thu, 15 Feb 2018 13:02:27 +0100 Message-Id: <1518696147-23790-1-git-send-email-ulrich.hecht+renesas@gmail.com> Sender: linux-renesas-soc-owner@vger.kernel.org List-ID: When the TTY buffers fill up to the configured maximum, a system lockup occurs: [ 598.820128] INFO: rcu_preempt detected stalls on CPUs/tasks: [ 598.825796] 0-...!: (1 GPs behind) idle=5a6/2/0 softirq=1974/1974 fqs=1 [ 598.832577] (detected by 3, t=62517 jiffies, g=296, c=295, q=126) [ 598.838755] Task dump for CPU 0: [ 598.841977] swapper/0 R running task 0 0 0 0x00000022 [ 598.849023] Call trace: [ 598.851476] __switch_to+0x98/0xb0 [ 598.854870] (null) This can be prevented by doing a dummy read of the RX data register. This issue affects both HSCIF and SCIF ports. Reported for R-Car H3 ES2.0; reproduced and fixed on H3 ES1.1. Probably affects other R-Car platforms as well. Reported-by: Yoshihiro Shimoda Signed-off-by: Ulrich Hecht --- drivers/tty/serial/sh-sci.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c index d9f399c..db2ebec 100644 --- a/drivers/tty/serial/sh-sci.c +++ b/drivers/tty/serial/sh-sci.c @@ -885,6 +885,8 @@ static void sci_receive_chars(struct uart_port *port) /* Tell the rest of the system the news. New characters! */ tty_flip_buffer_push(tport); } else { + /* TTY buffers full; read from RX reg to prevent lockup */ + serial_port_in(port, SCxRDR); serial_port_in(port, SCxSR); /* dummy read */ sci_clear_SCxSR(port, SCxSR_RDxF_CLEAR(port)); } -- 2.7.4