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serial: sh-sci: prevent lockup on full TTY buffers

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commit 7842055bfc 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>
This commit is contained in:
Ulrich Hecht
2018-02-15 13:02:27 +01:00
committed by Greg Kroah-Hartman
parent 6b0ce59be7
commit e79e49e76c
1 changed files with 2 additions and 0 deletions
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2
drivers/tty/serial/sh-sci.c
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@@ -847,6 +847,8 @@ 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));
}