watchdog: Separate and maintain variables based on variable lifetime

All variables required by the watchdog core to manage a watchdog are
currently stored in struct watchdog_device. The lifetime of those
variables is determined by the watchdog driver. However, the lifetime
of variables used by the watchdog core differs from the lifetime of
struct watchdog_device. To remedy this situation, watchdog drivers
can implement ref and unref callbacks, to be used by the watchdog
core to lock struct watchdog_device in memory.

While this solves the immediate problem, it depends on watchdog drivers
to actually implement the ref/unref callbacks. This is error prone,
often not implemented in the first place, or not implemented correctly.

To solve the problem without requiring driver support, split the variables
in struct watchdog_device into two data structures - one for variables
associated with the watchdog driver, one for variables associated with
the watchdog core. With this approach, the watchdog core can keep track
of its variable lifetime and no longer depends on ref/unref callbacks
in the driver. As a side effect, some of the variables originally in
struct watchdog_driver are now private to the watchdog core and no longer
visible in watchdog drivers.

As a side effect of the changes made, an ioctl will now always fail
with -ENODEV after a watchdog device was unregistered with the character
device still open. Previously, it would only fail with -ENODEV in some
situations. Also, ioctl operations are now atomic from driver perspective.
With this change, it is now guaranteed that the driver will not unregister
a watchdog between a timeout change and the subsequent ping.

The 'ref' and 'unref' callbacks in struct watchdog_driver are no longer
used and marked as deprecated.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

1 files changed, 8 insertions, 14 deletions

diff --git a/include/linux/watchdog.h b/include/linux/watchdog.h
index a88f955fde92..850af04fe0c7 100644
--- a/include/linux/watchdog.h
+++ b/include/linux/watchdog.h
@@ -17,6 +17,7 @@
 
 struct watchdog_ops;
 struct watchdog_device;
+struct watchdog_core_data;
 
 /** struct watchdog_ops - The watchdog-devices operations
  *
@@ -28,8 +29,6 @@ struct watchdog_device;
  * @set_timeout:The routine for setting the watchdog devices timeout value (in seconds).
  * @get_timeleft:The routine that gets the time left before a reset (in seconds).
  * @restart:	The routine for restarting the machine.
- * @ref:	The ref operation for dyn. allocated watchdog_device structs
- * @unref:	The unref operation for dyn. allocated watchdog_device structs
  * @ioctl:	The routines that handles extra ioctl calls.
  *
  * The watchdog_ops structure contains a list of low-level operations
@@ -48,15 +47,14 @@ struct watchdog_ops {
 	int (*set_timeout)(struct watchdog_device *, unsigned int);
 	unsigned int (*get_timeleft)(struct watchdog_device *);
 	int (*restart)(struct watchdog_device *);
-	void (*ref)(struct watchdog_device *);
-	void (*unref)(struct watchdog_device *);
+	void (*ref)(struct watchdog_device *) __deprecated;
+	void (*unref)(struct watchdog_device *) __deprecated;
 	long (*ioctl)(struct watchdog_device *, unsigned int, unsigned long);
 };
 
 /** struct watchdog_device - The structure that defines a watchdog device
  *
  * @id:		The watchdog's ID. (Allocated by watchdog_register_device)
- * @cdev:	The watchdog's Character device.
  * @dev:	The device for our watchdog
  * @parent:	The parent bus device
  * @info:	Pointer to a watchdog_info structure.
@@ -67,8 +65,8 @@ struct watchdog_ops {
  * @max_timeout:The watchdog devices maximum timeout value (in seconds).
  * @reboot_nb:	The notifier block to stop watchdog on reboot.
  * @restart_nb:	The notifier block to register a restart function.
- * @driver-data:Pointer to the drivers private data.
- * @lock:	Lock for watchdog core internal use only.
+ * @driver_data:Pointer to the drivers private data.
+ * @wd_data:	Pointer to watchdog core internal data.
  * @status:	Field that contains the devices internal status bits.
  * @deferred: entry in wtd_deferred_reg_list which is used to
  *			   register early initialized watchdogs.
@@ -84,7 +82,6 @@ struct watchdog_ops {
  */
 struct watchdog_device {
 	int id;
-	struct cdev cdev;
 	struct device *dev;
 	struct device *parent;
 	const struct watchdog_info *info;
@@ -96,15 +93,12 @@ struct watchdog_device {
 	struct notifier_block reboot_nb;
 	struct notifier_block restart_nb;
 	void *driver_data;
-	struct mutex lock;
+	struct watchdog_core_data *wd_data;
 	unsigned long status;
 /* Bit numbers for status flags */
 #define WDOG_ACTIVE		0	/* Is the watchdog running/active */
-#define WDOG_DEV_OPEN		1	/* Opened via /dev/watchdog ? */
-#define WDOG_ALLOW_RELEASE	2	/* Did we receive the magic char ? */
-#define WDOG_NO_WAY_OUT		3	/* Is 'nowayout' feature set ? */
-#define WDOG_UNREGISTERED	4	/* Has the device been unregistered */
-#define WDOG_STOP_ON_REBOOT	5	/* Should be stopped on reboot */
+#define WDOG_NO_WAY_OUT		1	/* Is 'nowayout' feature set ? */
+#define WDOG_STOP_ON_REBOOT	2	/* Should be stopped on reboot */
 	struct list_head deferred;
 };