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Subject[PATCH 1/2] watchdog: Check WDOG_STOP_ON_REBOOT in reboot notifier
Date
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@arista.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
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