linux-kernel - [PATCH 1/2] watchdog: Check WDOG_STOP_ON

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Message-Id: <20200213175958.105914-2-dima@arista.com>
Date:   Thu, 13 Feb 2020 17:59:57 +0000
From:   Dmitry Safonov <dima@...sta.com>
To:     linux-kernel@...r.kernel.org
Cc:     Dmitry Safonov <0x7f454c46@...il.com>,
        Dmitry Safonov <dima@...sta.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        linux-watchdog@...r.kernel.org
Subject: [PATCH 1/2] watchdog: Check WDOG_STOP_ON_REBOOT in reboot notifier

Many watchdog drivers use watchdog_stop_on_reboot() helper in order
to stop the watchdog on system reboot. Unfortunately, this logic is
coded in driver's probe function and doesn't allows user to decide what
to do during shutdown/reboot.

On the other side, Xen and Qemu watchdog drivers (xen_wdt and i6300esb)
may be configured to either send NMI or turn off/reboot VM as
the watchdog action. As the kernel may stuck at any state, sending NMIs
can't reliably reboot the VM.

At Arista, we benefited from the following set-up: the emulated watchdogs
trigger VM reset and softdog is set to catch less severe conditions to
generate vmcore. Just before reboot watchdog's timeout is increased
to some good-enough value (3 mins). That keeps watchdog always running
and guarantees that VM doesn't stuck.

As a preparation to move the watchdog's decision to stop on reboot or
not in userspace, allow WDOG_STOP_ON_REBOOT to be set during runtime,
not only on driver's probing. Always register reboot notifier and check
WDOG_STOP_ON_REBOOT inside it (on actual reboot).

Signed-off-by: Dmitry Safonov <dima@...sta.com>
---
 drivers/watchdog/watchdog_core.c | 27 +++++++++++++--------------
 1 file changed, 13 insertions(+), 14 deletions(-)

diff --git a/drivers/watchdog/watchdog_core.c b/drivers/watchdog/watchdog_core.c
index 861daf4f37b2..ebf80ff3e8ce 100644
--- a/drivers/watchdog/watchdog_core.c
+++ b/drivers/watchdog/watchdog_core.c
@@ -153,6 +153,10 @@ static int watchdog_reboot_notifier(struct notifier_block *nb,
 	struct watchdog_device *wdd;

 	wdd = container_of(nb, struct watchdog_device, reboot_nb);
+
+	if (!test_bit(WDOG_STOP_ON_REBOOT, &wdd->status))
+		return NOTIFY_DONE;
+
 	if (code == SYS_DOWN || code == SYS_HALT) {
 		if (watchdog_active(wdd)) {
 			int ret;
@@ -254,17 +258,14 @@ static int __watchdog_register_device(struct watchdog_device *wdd)
 		}
 	}

-	if (test_bit(WDOG_STOP_ON_REBOOT, &wdd->status)) {
-		wdd->reboot_nb.notifier_call = watchdog_reboot_notifier;
-
-		ret = register_reboot_notifier(&wdd->reboot_nb);
-		if (ret) {
-			pr_err("watchdog%d: Cannot register reboot notifier (%d)\n",
-			       wdd->id, ret);
-			watchdog_dev_unregister(wdd);
-			ida_simple_remove(&watchdog_ida, id);
-			return ret;
-		}
+	wdd->reboot_nb.notifier_call = watchdog_reboot_notifier;
+	ret = register_reboot_notifier(&wdd->reboot_nb);
+	if (ret) {
+		pr_err("watchdog%d: Cannot register reboot notifier (%d)\n",
+				wdd->id, ret);
+		watchdog_dev_unregister(wdd);
+		ida_simple_remove(&watchdog_ida, id);
+		return ret;
 	}

 	if (wdd->ops->restart) {
@@ -321,9 +322,7 @@ static void __watchdog_unregister_device(struct watchdog_device *wdd)
 	if (wdd->ops->restart)
 		unregister_restart_handler(&wdd->restart_nb);

-	if (test_bit(WDOG_STOP_ON_REBOOT, &wdd->status))
-		unregister_reboot_notifier(&wdd->reboot_nb);
-
+	unregister_reboot_notifier(&wdd->reboot_nb);
 	watchdog_dev_unregister(wdd);
 	ida_simple_remove(&watchdog_ida, wdd->id);
 }
-- 
2.25.0