[ 3.5.y.z extended stable ] Patch "serial_core.c: add put_device() after device_find_child()" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    serial_core.c: add put_device() after device_find_child()

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 2cbe34ff5f1d2671da47d5fa4e6e13a503c4f56e Mon Sep 17 00:00:00 2001
From: Federico Vaga <federico.vaga at gmail.com>
Date: Mon, 15 Apr 2013 16:01:07 +0200
Subject: [PATCH] serial_core.c: add put_device() after device_find_child()

commit 5a65dcc04cda41f4122aacc37a5a348454645399 upstream.

The serial core uses device_find_child() but does not drop the reference to
the retrieved child after using it. This patch add the missing put_device().

What I have done to test this issue.

I used a machine with an AMBA PL011 serial driver. I tested the patch on
next-20120408 because the last branch [next-20120415] does not boot on this
board.

For test purpose, I added some pr_info() messages to print the refcount
after device_find_child() (lines: 1937,2009), and after put_device()
(lines: 1947, 2021).

Boot the machine *without* put_device(). Then:

echo reboot > /sys/power/disk
echo disk > /sys/power/state
[   87.058575] uart_suspend_port:1937 refcount 4
[   87.058582] uart_suspend_port:1947 refcount 4
[   87.098083] uart_resume_port:2009refcount 5
[   87.098088] uart_resume_port:2021 refcount 5

echo disk > /sys/power/state
[  103.055574] uart_suspend_port:1937 refcount 6
[  103.055580] uart_suspend_port:1947 refcount 6
[  103.095322] uart_resume_port:2009 refcount 7
[  103.095327] uart_resume_port:2021 refcount 7

echo disk > /sys/power/state
[  252.459580] uart_suspend_port:1937 refcount 8
[  252.459586] uart_suspend_port:1947 refcount 8
[  252.499611] uart_resume_port:2009 refcount 9
[  252.499616] uart_resume_port:2021 refcount 9

The refcount continuously increased.

Boot the machine *with* this patch. Then:

echo reboot > /sys/power/disk
echo disk > /sys/power/state
[  159.333559] uart_suspend_port:1937 refcount 4
[  159.333566] uart_suspend_port:1947 refcount 3
[  159.372751] uart_resume_port:2009 refcount 4
[  159.372755] uart_resume_port:2021 refcount 3

echo disk > /sys/power/state
[  185.713614] uart_suspend_port:1937 refcount 4
[  185.713621] uart_suspend_port:1947 refcount 3
[  185.752935] uart_resume_port:2009 refcount 4
[  185.752940] uart_resume_port:2021 refcount 3

echo disk > /sys/power/state
[  207.458584] uart_suspend_port:1937 refcount 4
[  207.458591] uart_suspend_port:1947 refcount 3
[  207.498598] uart_resume_port:2009 refcount 4
[  207.498605] uart_resume_port:2021 refcount 3

The refcount correctly handled.

Signed-off-by: Federico Vaga <federico.vaga at gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/tty/serial/serial_core.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 246b823..4185cc5 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -1877,6 +1877,8 @@ int uart_suspend_port(struct uart_driver *drv, struct uart_port *uport)
 		mutex_unlock(&port->mutex);
 		return 0;
 	}
+	put_device(tty_dev);
+
 	if (console_suspend_enabled || !uart_console(uport))
 		uport->suspended = 1;

@@ -1942,9 +1944,11 @@ int uart_resume_port(struct uart_driver *drv, struct uart_port *uport)
 			disable_irq_wake(uport->irq);
 			uport->irq_wake = 0;
 		}
+		put_device(tty_dev);
 		mutex_unlock(&port->mutex);
 		return 0;
 	}
+	put_device(tty_dev);
 	uport->suspended = 0;

 	/*
--
1.8.1.2