On Wed, 2017-10-04 at 16:40 +0200, Maxim Yu. Osipov wrote:

From: Guenter Roeck <linux@...>

Backport from kernel.org, upstream commit ee142889e32f

The WDOG_HW_RUNNING flag is expected to be set by watchdog drivers if
the hardware watchdog is running. If the flag is set, the watchdog
subsystem will ping the watchdog even if the watchdog device is
closed.

The watchdog driver stop function is now optional and may be omitted
if the watchdog can not be stopped. If stopping the watchdog is not
possible but the driver implements a stop function, it is responsible
to set the WDOG_HW_RUNNING flag in its stop function.

[...]

--- a/drivers/watchdog/watchdog_dev.c
+++ b/drivers/watchdog/watchdog_dev.c

[...]

@@ -651,9 +665,24 @@ int watchdog_dev_register(struct watchdog_device
*wdd)
  if (wdd->id == 0) {
  misc_deregister(&watchdog_miscdev);
  old_wdd = NULL;
+ if (wdd->ops->unref)
+ wdd->ops->unref(wdd);

[...]

This doesn't look right. This is decrementing a reference counter
because the old_wdd reference is going away, but we never increment a
reference counter when old_wdd is set.

The upstream commit doesn't make any change here. There is a
kref_put() here in the upstream version but that was added as part of
the watchdog_device/watchdog_core_data split.

Ben.

--
Ben Hutchings
Software Developer, Codethink Ltd.