[PATCH 3.16 009/134] serial: sh-sci: Fix panic when serial console and DMA are enabled

Ben Hutchings
2017-08-18T13:15:41Z

From: Takatoshi Akiyama <takatoshi.akiyama.kj@ps.hitachi-solutions.com>

commit 3c9101766b502a0163d1d437fada5801cf616be2 upstream.

This patch fixes an issue that kernel panic happens when DMA is enabled
and we press enter key while the kernel booting on the serial console.

* An interrupt may occur after sci_request_irq().
* DMA transfer area is initialized by setup_timer() in sci_request_dma()
and used in interrupt.

If an interrupt occurred between sci_request_irq() and setup_timer() in
sci_request_dma(), DMA transfer area has not been initialized yet.
So, this patch changes the order of sci_request_irq() and
sci_request_dma().

Fixes: 73a19e4c0301 ("serial: sh-sci: Add DMA support.")
Signed-off-by: Takatoshi Akiyama <takatoshi.akiyama.kj@ps.hitachi-solutions.com>
[Shimoda changes the commit log]
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/tty/serial/sh-sci.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)

--- a/drivers/tty/serial/sh-sci.c
+++ b/drivers/tty/serial/sh-sci.c
@@ -1715,11 +1715,13 @@ static int sci_startup(struct uart_port

dev_dbg(port->dev, "%s(%d)\n", __func__, port->line);

+ sci_request_dma(port);
+
ret = sci_request_irq(s);
- if (unlikely(ret < 0))
+ if (unlikely(ret < 0)) {
+ sci_free_dma(port);
return ret;
-
- sci_request_dma(port);
+ }

spin_lock_irqsave(&port->lock, flags);
sci_start_tx(port);
@@ -1741,8 +1743,8 @@ static void sci_shutdown(struct uart_por
sci_stop_tx(port);
spin_unlock_irqrestore(&port->lock, flags);

- sci_free_dma(port);
sci_free_irq(s);
+ sci_free_dma(port);
}

static unsigned int sci_scbrr_calc(struct sci_port *s, unsigned int bps,