linux-kernel - [PATCH 3.18 38/45] serial: sh-sci: Fix panic when serial console and DMA are enabled

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Message-Id: <20170612152555.435852347@linuxfoundation.org>
Date:   Mon, 12 Jun 2017 17:26:48 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Takatoshi Akiyama <takatoshi.akiyama.kj@...hitachi-solutions.com>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.18 38/45] serial: sh-sci: Fix panic when serial console and DMA are enabled

3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Takatoshi Akiyama <takatoshi.akiyama.kj@...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@...hitachi-solutions.com>
[Shimoda changes the commit log]
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
Cc: Jiri Slaby <jslaby@...e.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 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
@@ -1734,11 +1734,13 @@ 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);
@@ -1760,8 +1762,8 @@ 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,