From: Stelian Pop <stelian@popies.net>

> Well, 2 processes simultaneously enabling and disabling input device
> will mess up the driver; some locking is needed there. Pretty extreme,
> I know...

Right. The input_mutex in the patch below should fix this issue.

Cc: Stelian Pop <stelian@popies.net>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Dmitry Torokhov <dtor_core@ameritech.net>
Cc: Robert Love <rml@novell.com>
Cc: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---

 drivers/hwmon/ams.c |   26 ++++++++++++++++++++------
 1 file changed, 20 insertions(+), 6 deletions(-)

diff -puN drivers/hwmon/ams.c~apple-motion-sensor-driver-update-2 drivers/hwmon/ams.c
--- a/drivers/hwmon/ams.c~apple-motion-sensor-driver-update-2
+++ a/drivers/hwmon/ams.c
@@ -1,7 +1,7 @@
 /*
  * Apple Motion Sensor driver
  *
- * Copyright (C) 2006 Stelian Pop (stelian@popies.net)
+ * Copyright (C) 2005 Stelian Pop (stelian@popies.net)
  *
  * Clean room implementation based on the reverse engineered OSX driver by
  * Johannes Berg <johannes@sipsolutions.net>, documentation available at
@@ -101,6 +101,7 @@ struct ams {
 	int			xcalib;		/* calibrated null value for x */
 	int			ycalib;		/* calibrated null value for y */
 	int			zcalib;		/* calibrated null value for z */
+	struct mutex		input_mutex;
 	struct task_struct	*kthread;	/* kthread for input */
 };
 
@@ -226,8 +227,10 @@ static void ams_mouse_enable(void)
 {
 	s8 x, y, z;
 
+	mutex_lock(&ams.input_mutex);
+
 	if (ams.idev)
-		return;
+		goto out;
 
 	ams_sensors(&x, &y, &z);
 	ams.xcalib = x;
@@ -236,7 +239,7 @@ static void ams_mouse_enable(void)
 
 	ams.idev = input_allocate_device();
 	if (!ams.idev)
-		return;
+		goto out;
 
 	ams.idev->name = "Apple Motion Sensor";
 	ams.idev->id.bustype = BUS_I2C;
@@ -253,27 +256,33 @@ static void ams_mouse_enable(void)
 	if (input_register_device(ams.idev)) {
 		input_free_device(ams.idev);
 		ams.idev = NULL;
-		return;
+		goto out;
 	}
 
 	ams.kthread = kthread_run(ams_mouse_kthread, NULL, "kams");
 	if (IS_ERR(ams.kthread)) {
 		input_unregister_device(ams.idev);
 		ams.idev = NULL;
-		return;
+		goto out;
 	}
+out:
+	mutex_unlock(&ams.input_mutex);
 }
 
 static void ams_mouse_disable(void)
 {
+	mutex_lock(&ams.input_mutex);
+
 	if (!ams.idev)
-		return;
+		goto out;
 
 	kthread_stop(ams.kthread);
 
 	input_unregister_device(ams.idev);
 
 	ams.idev = NULL;
+out:
+	mutex_unlock(&ams.input_mutex);
 }
 
 static ssize_t ams_show_mouse(struct device *dev, struct device_attribute *attr,
@@ -488,6 +497,8 @@ static int __init ams_init(void)
 	if ((ams.of_dev = of_platform_device_create(np, "ams", NULL)) == NULL)
 		goto free_irq2;
 
+	mutex_init(&ams.input_mutex);
+
 	device_create_file(&ams.of_dev->dev, &dev_attr_x);
 	device_create_file(&ams.of_dev->dev, &dev_attr_y);
 	device_create_file(&ams.of_dev->dev, &dev_attr_z);
@@ -503,6 +514,7 @@ free_device_files:
 	device_remove_file(&ams.of_dev->dev, &dev_attr_y);
 	device_remove_file(&ams.of_dev->dev, &dev_attr_z);
 	device_remove_file(&ams.of_dev->dev, &dev_attr_mouse);
+	mutex_destroy(&ams.input_mutex);
 free_irq2:
 	free_irq(ams.irq2, NULL);
 free_irq1:
@@ -523,6 +535,8 @@ static void __exit ams_exit(void)
 	device_remove_file(&ams.of_dev->dev, &dev_attr_z);
 	device_remove_file(&ams.of_dev->dev, &dev_attr_mouse);
 
+	mutex_destroy(&ams.input_mutex);
+
 	of_device_unregister(ams.of_dev);
 }
 
_