[PATCH v2] drivers: watchdog: Add support for panic notifier callback

[George Cherian <george.cherian@xxxxxxxxxxx>]

Watchdog is not turned off in kernel panic situation.
In certain systems this might prevent the successful loading
of kdump kernel. The kdump kernel might hit a watchdog reset
while it is booting.

To avoid such scenarios add a panic notifier call back function
which can stop the watchdog. This provision can be enabled by
passing watchdog.stop_on_panic=1 via kernel command-line parameter.

Signed-off-by: George Cherian <george.cherian@xxxxxxxxxxx>
---
Changelog:
v1 -> v2
- Remove the per driver flag setting option
- Take the parameter via kernel command-line parameter to watchdog_core.

 drivers/watchdog/watchdog_core.c | 42 ++++++++++++++++++++++++++++++++
 include/linux/watchdog.h         |  8 ++++++
 2 files changed, 50 insertions(+)

diff --git a/drivers/watchdog/watchdog_core.c b/drivers/watchdog/watchdog_core.c
index d46d8c8c01f2..8cbebe38b7dd 100644
--- a/drivers/watchdog/watchdog_core.c
+++ b/drivers/watchdog/watchdog_core.c
@@ -34,6 +34,7 @@
 #include <linux/idr.h>		/* For ida_* macros */
 #include <linux/err.h>		/* For IS_ERR macros */
 #include <linux/of.h>		/* For of_get_timeout_sec */
+#include <linux/panic_notifier.h> /* For panic handler */
 #include <linux/suspend.h>
 
 #include "watchdog_core.h"	/* For watchdog_dev_register/... */
@@ -47,6 +48,9 @@ static int stop_on_reboot = -1;
 module_param(stop_on_reboot, int, 0444);
 MODULE_PARM_DESC(stop_on_reboot, "Stop watchdogs on reboot (0=keep watching, 1=stop)");
 
+static int stop_on_panic = -1;
+module_param(stop_on_panic, int, 0444);
+MODULE_PARM_DESC(stop_on_panic, "Stop watchdogs on panic (0=keep watching, 1=stop)");
 /*
  * Deferred Registration infrastructure.
  *
@@ -155,6 +159,23 @@ int watchdog_init_timeout(struct watchdog_device *wdd,
 }
 EXPORT_SYMBOL_GPL(watchdog_init_timeout);
 
+static int watchdog_panic_notify(struct notifier_block *nb,
+				 unsigned long action, void *data)
+{
+	struct watchdog_device *wdd;
+
+	wdd = container_of(nb, struct watchdog_device, panic_nb);
+	if (watchdog_active(wdd)) {
+		int ret;
+
+		ret = wdd->ops->stop(wdd);
+		if (ret)
+			return NOTIFY_BAD;
+	}
+
+	return NOTIFY_DONE;
+}
+
 static int watchdog_reboot_notifier(struct notifier_block *nb,
 				    unsigned long code, void *data)
 {
@@ -299,6 +320,14 @@ static int ___watchdog_register_device(struct watchdog_device *wdd)
 			clear_bit(WDOG_STOP_ON_REBOOT, &wdd->status);
 	}
 
+	/* Module parameter to force watchdog policy on panic. */
+	if (stop_on_panic != -1) {
+		if (stop_on_panic &&  !test_bit(WDOG_NO_WAY_OUT, &wdd->status))
+			set_bit(WDOG_STOP_ON_PANIC, &wdd->status);
+		else
+			clear_bit(WDOG_STOP_ON_PANIC, &wdd->status);
+	}
+
 	if (test_bit(WDOG_STOP_ON_REBOOT, &wdd->status)) {
 		if (!wdd->ops->stop)
 			pr_warn("watchdog%d: stop_on_reboot not supported\n", wdd->id);
@@ -334,6 +363,16 @@ static int ___watchdog_register_device(struct watchdog_device *wdd)
 				wdd->id, ret);
 	}
 
+	if (test_bit(WDOG_STOP_ON_PANIC, &wdd->status)) {
+		if (!wdd->ops->stop) {
+			pr_warn("watchdog%d: stop_on_panic not supported\n", wdd->id);
+		} else {
+			wdd->panic_nb.notifier_call = watchdog_panic_notify;
+			atomic_notifier_chain_register(&panic_notifier_list,
+						       &wdd->panic_nb);
+		}
+	}
+
 	return 0;
 }
 
@@ -390,6 +429,9 @@ static void __watchdog_unregister_device(struct watchdog_device *wdd)
 	if (test_bit(WDOG_STOP_ON_REBOOT, &wdd->status))
 		unregister_reboot_notifier(&wdd->reboot_nb);
 
+	if (test_bit(WDOG_STOP_ON_PANIC, &wdd->status))
+		atomic_notifier_chain_unregister(&panic_notifier_list,
+						 &wdd->panic_nb);
 	watchdog_dev_unregister(wdd);
 	ida_free(&watchdog_ida, wdd->id);
 }
diff --git a/include/linux/watchdog.h b/include/linux/watchdog.h
index 99660197a36c..3c21b527ede9 100644
--- a/include/linux/watchdog.h
+++ b/include/linux/watchdog.h
@@ -108,6 +108,7 @@ struct watchdog_device {
 	struct notifier_block reboot_nb;
 	struct notifier_block restart_nb;
 	struct notifier_block pm_nb;
+	struct notifier_block panic_nb;
 	void *driver_data;
 	struct watchdog_core_data *wd_data;
 	unsigned long status;
@@ -118,6 +119,7 @@ struct watchdog_device {
 #define WDOG_HW_RUNNING		3	/* True if HW watchdog running */
 #define WDOG_STOP_ON_UNREGISTER	4	/* Should be stopped on unregister */
 #define WDOG_NO_PING_ON_SUSPEND	5	/* Ping worker should be stopped on suspend */
+#define WDOG_STOP_ON_PANIC	6	/* Should be stopped on panic for loading kdump kernels */
 	struct list_head deferred;
 };
 
@@ -146,6 +148,12 @@ static inline void watchdog_set_nowayout(struct watchdog_device *wdd, bool noway
 		set_bit(WDOG_NO_WAY_OUT, &wdd->status);
 }
 
+/* Use the following function to stop the watchdog on panic */
+static inline void watchdog_stop_on_panic(struct watchdog_device *wdd)
+{
+	set_bit(WDOG_STOP_ON_PANIC, &wdd->status);
+}
+
 /* Use the following function to stop the watchdog on reboot */
 static inline void watchdog_stop_on_reboot(struct watchdog_device *wdd)
 {
-- 
2.34.1