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Commit f4e9c82f authored by Hans de Goede's avatar Hans de Goede Committed by Wim Van Sebroeck
Browse files

watchdog: Add Locking support 



This patch fixes some potential multithreading issues, despite only
allowing one process to open the /dev/watchdog device, we can still get
called multiple times at the same time, since a program could be using thread,
or could share the fd after a fork.

This causes 2 potential problems:
1) watchdog_start / open do an unlocked test_n_set / test_n_clear,
   if these 2 race, the watchdog could be stopped while the active
   bit indicates it is running or visa versa.

2) Most watchdog_dev drivers probably assume that only one
   watchdog-op will get called at a time, this is not necessary
   true atm.

Signed-off-by: default avatarHans de Goede <hdegoede@redhat.com>
Signed-off-by: default avatarWim Van Sebroeck <wim@iguana.be>
parent 7a879824

Documentation/watchdog/watchdog-kernel-api.txt

+2 −0
Original line number Diff line number Diff line
@@ -50,6 +50,7 @@ struct watchdog_device { 
	unsigned int min_timeout;

	unsigned int max_timeout;

	void *driver_data;

	struct mutex lock;

	unsigned long status;

};
@@ -74,6 +75,7 @@ It contains following fields: 
* driver_data: a pointer to the drivers private data of a watchdog device.

  This data should only be accessed via the watchdog_set_drvdata and

  watchdog_get_drvdata routines.

* lock: Mutex for WatchDog Timer Driver Core internal use only.

* status: this field contains a number of status bits that give extra

  information about the status of the device (Like: is the watchdog timer

  running/active, is the nowayout bit set, is the device opened via

drivers/watchdog/watchdog_core.c

+1 −0
Original line number Diff line number Diff line
@@ -79,6 +79,7 @@ int watchdog_register_device(struct watchdog_device *wdd) 
	 * corrupted in a later stage then we expect a kernel panic!

	 */



	mutex_init(&wdd->lock);

	id = ida_simple_get(&watchdog_ida, 0, MAX_DOGS, GFP_KERNEL);

	if (id < 0)

		return id;

drivers/watchdog/watchdog_dev.c

+21 −0
Original line number Diff line number Diff line
@@ -63,6 +63,8 @@ static int watchdog_ping(struct watchdog_device *wddev) 
{

	int err = 0;



	mutex_lock(&wddev->lock);



	if (!watchdog_active(wddev))

		goto out_ping;
@@ -72,6 +74,7 @@ static int watchdog_ping(struct watchdog_device *wddev) 
		err = wddev->ops->start(wddev); /* restart watchdog */



out_ping:

	mutex_unlock(&wddev->lock);

	return err;

}
@@ -88,6 +91,8 @@ static int watchdog_start(struct watchdog_device *wddev) 
{

	int err = 0;



	mutex_lock(&wddev->lock);



	if (watchdog_active(wddev))

		goto out_start;
@@ -96,6 +101,7 @@ static int watchdog_start(struct watchdog_device *wddev) 
		set_bit(WDOG_ACTIVE, &wddev->status);



out_start:

	mutex_unlock(&wddev->lock);

	return err;

}
@@ -113,6 +119,8 @@ static int watchdog_stop(struct watchdog_device *wddev) 
{

	int err = 0;



	mutex_lock(&wddev->lock);



	if (!watchdog_active(wddev))

		goto out_stop;
@@ -127,6 +135,7 @@ static int watchdog_stop(struct watchdog_device *wddev) 
		clear_bit(WDOG_ACTIVE, &wddev->status);



out_stop:

	mutex_unlock(&wddev->lock);

	return err;

}
@@ -147,8 +156,11 @@ static int watchdog_get_status(struct watchdog_device *wddev, 
	if (!wddev->ops->status)

		return -EOPNOTSUPP;



	mutex_lock(&wddev->lock);



	*status = wddev->ops->status(wddev);



	mutex_unlock(&wddev->lock);

	return err;

}
@@ -171,8 +183,11 @@ static int watchdog_set_timeout(struct watchdog_device *wddev, 
	    (timeout < wddev->min_timeout || timeout > wddev->max_timeout))

		return -EINVAL;



	mutex_lock(&wddev->lock);



	err = wddev->ops->set_timeout(wddev, timeout);



	mutex_unlock(&wddev->lock);

	return err;

}
@@ -193,8 +208,11 @@ static int watchdog_get_timeleft(struct watchdog_device *wddev, 
	if (!wddev->ops->get_timeleft)

		return -EOPNOTSUPP;



	mutex_lock(&wddev->lock);



	*timeleft = wddev->ops->get_timeleft(wddev);



	mutex_unlock(&wddev->lock);

	return err;

}
@@ -213,8 +231,11 @@ static int watchdog_ioctl_op(struct watchdog_device *wddev, unsigned int cmd, 
	if (!wddev->ops->ioctl)

		return -ENOIOCTLCMD;



	mutex_lock(&wddev->lock);



	err = wddev->ops->ioctl(wddev, cmd, arg);



	mutex_unlock(&wddev->lock);

	return err;

}

include/linux/watchdog.h

+5 −0
Original line number Diff line number Diff line
@@ -104,6 +104,7 @@ struct watchdog_ops { 
 * @min_timeout:The watchdog devices minimum timeout value.

 * @max_timeout:The watchdog devices maximum timeout value.

 * @driver-data:Pointer to the drivers private data.

 * @lock:	Lock for watchdog core internal use only.

 * @status:	Field that contains the devices internal status bits.

 *

 * The watchdog_device structure contains all information about a
@@ -111,6 +112,9 @@ struct watchdog_ops { 
 *

 * The driver-data field may not be accessed directly. It must be accessed

 * via the watchdog_set_drvdata and watchdog_get_drvdata helpers.

 *

 * The lock field is for watchdog core internal use only and should not be

 * touched.

 */

struct watchdog_device {

	int id;
@@ -124,6 +128,7 @@ struct watchdog_device { 
	unsigned int min_timeout;

	unsigned int max_timeout;

	void *driver_data;

	struct mutex lock;

	unsigned long status;

/* Bit numbers for status flags */

#define WDOG_ACTIVE		0	/* Is the watchdog running/active */