linux-kernel - [PATCH] atmel_serial: fix spinlock lockup in RS485 code

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Date:	Thu, 15 Dec 2011 09:47:43 +0100
From:	Claudio Scordino <claudio@...dence.eu.com>
To:	Nicolas Ferre <nicolas.ferre@...el.com>,
	Alan Cox <alan@...ux.intel.com>
CC:	Linux Kernel <linux-kernel@...r.kernel.org>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
	Dave Bender <codehero@...il.com>
Subject: [PATCH] atmel_serial: fix spinlock lockup in RS485 code

Hi all.

We have encountered a spinlock lockup in the RS485 part of the atmel_serial driver.

Here is the trace:

[   68.030000] BUG: spinlock lockup on CPU#0, dnp_master/244, c07e82c0
[   68.040000] [<c002a790>] (unwind_backtrace+0x0/0xf0) from [<c012f8f0>] (do_raw_spin_lock+0x10c/0x148)
[   68.050000] [<c012f8f0>] (do_raw_spin_lock+0x10c/0x148) from [<c015152c>] (atmel_tasklet_func+0x10/0x708)
[   68.060000] [<c015152c>] (atmel_tasklet_func+0x10/0x708) from [<c003bfd4>] (tasklet_action+0x8c/0xf4)
[   68.070000] [<c003bfd4>] (tasklet_action+0x8c/0xf4) from [<c003c630>] (__do_softirq+0xa4/0x180)
[   68.080000] [<c003c630>] (__do_softirq+0xa4/0x180) from [<c003c764>] (irq_exit+0x58/0xb0)
[   68.090000] [<c003c764>] (irq_exit+0x58/0xb0) from [<c0021084>] (asm_do_IRQ+0x84/0xa4)
[   68.100000] [<c0021084>] (asm_do_IRQ+0x84/0xa4) from [<c002622c>] (__irq_svc+0x4c/0x98)
[   68.110000] Exception stack(0xc341fdc8 to 0xc341fe10)
[   68.110000] fdc0:                   c07e82c0 00000000 00000200 c4818000 c341fe10 c07e82c0
[   68.120000] fde0: 00000000 c07e82c0 c38d3318 c341e000 bebcee00 010a0b60 c07e83fc c341fe10
[   68.130000] fe00: c0151d54 c023d9c0 60000013 ffffffff
[   68.140000] [<c002622c>] (__irq_svc+0x4c/0x98) from [<c023d9c0>] (_raw_spin_unlock+0x0/0x48)
[   68.140000] [<c023d9c0>] (_raw_spin_unlock+0x0/0x48) from [<00000000>] (  (null))

The soft lockup occurs later

[  126.750000] BUG: soft lockup - CPU#0 stuck for 61s! [dnp_master:244]
[  126.750000] irq event stamp: 0
[  126.750000] hardirqs last  enabled at (0): [<  (null)>]   (null)
[  126.750000] hardirqs last disabled at (0): [<c0035e30>] copy_process+0x308/0xe78
[  126.750000] softirqs last  enabled at (0): [<c0035e30>] copy_process+0x308/0xe78
[  126.750000] softirqs last disabled at (0): [<  (null)>]   (null)


The following patch (already tested by Dave, who also reported the bug) fixes the problem.

Regards,

	Claudio




Subject: atmel_serial: fix spinlock lockup in RS485 code

Patch to fix a spinlock lockup in the driver that sometimes happens when the
tasklet starts.

Signed-off-by: Claudio Scordino <claudio@...dence.eu.com>
Signed-off-by: Dave Bender <codehero@...il.com>
Tested-by: Dave Bender <codehero@...il.com>
---
  drivers/tty/serial/atmel_serial.c |    5 +++--
  1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
index 4c823f3..90c8e3a 100644
--- a/drivers/tty/serial/atmel_serial.c
+++ b/drivers/tty/serial/atmel_serial.c
@@ -212,8 +212,9 @@ void atmel_config_rs485(struct uart_port *port, struct serial_rs485 *rs485conf)
  {
  	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
  	unsigned int mode;
+	unsigned long flags;
  
-	spin_lock(&port->lock);
+	spin_lock_irqsave(&port->lock, flags);
  
  	/* Disable interrupts */
  	UART_PUT_IDR(port, atmel_port->tx_done_mask);
@@ -244,7 +245,7 @@ void atmel_config_rs485(struct uart_port *port, struct serial_rs485 *rs485conf)
  	/* Enable interrupts */
  	UART_PUT_IER(port, atmel_port->tx_done_mask);
  
-	spin_unlock(&port->lock);
+	spin_unlock_irqrestore(&port->lock, flags);
  
  }
  
-- 
1.7.1


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