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Message-ID: <lsq.1528380321.197204780@decadent.org.uk>
Date: Thu, 07 Jun 2018 15:05:21 +0100
From: Ben Hutchings <ben@...adent.org.uk>
To: linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC: akpm@...ux-foundation.org,
"Geert Uytterhoeven" <geert+renesas@...der.be>,
"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
"Ulrich Hecht" <ulrich.hecht+renesas@...il.com>,
"Nguyen Viet Dung" <dung.nguyen.aj@...esas.com>,
"Yoshihiro Shimoda" <yoshihiro.shimoda.uh@...esas.com>
Subject: [PATCH 3.16 308/410] serial: sh-sci: prevent lockup on full TTY
buffers
3.16.57-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: Ulrich Hecht <ulrich.hecht+renesas@...il.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@...esas.com>
Signed-off-by: Ulrich Hecht <ulrich.hecht+renesas@...il.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.be>
Tested-by: Nguyen Viet Dung <dung.nguyen.aj@...esas.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
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
@@ -734,6 +734,8 @@ 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 */
serial_port_out(port, SCxSR, SCxSR_RDxF_CLEAR(port));
}
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