4.9-stable review patch. If anyone has any objections, please let me know.
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From: Ulrich Hecht ulrich.hecht+renesas@gmail.com
commit 7842055bfce4bf0170d0f61df8b2add8399697be upstream.
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(+)
--- a/drivers/tty/serial/sh-sci.c +++ b/drivers/tty/serial/sh-sci.c @@ -935,6 +935,8 @@ static void sci_receive_chars(struct uar /* 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)); }