This is a note to let you know that I've just added the patch titled
serial: sh-sci: prevent lockup on full TTY buffers
to my tty git tree which can be found at git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git in the tty-linus branch.
The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)
The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.
If you have any questions about this process, please let me know.
From 7842055bfce4bf0170d0f61df8b2add8399697be Mon Sep 17 00:00:00 2001
From: Ulrich Hecht ulrich.hecht+renesas@gmail.com Date: Thu, 15 Feb 2018 13:02:27 +0100 Subject: serial: sh-sci: prevent lockup on full TTY buffers
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 yoshihiro.shimoda.uh@renesas.com Signed-off-by: Ulrich Hecht ulrich.hecht+renesas@gmail.com Reviewed-by: Geert Uytterhoeven geert+renesas@glider.be Cc: stable stable@vger.kernel.org Tested-by: Nguyen Viet Dung dung.nguyen.aj@renesas.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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 7257c078e155..44adf9db38f8 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)); }