was [Re: [PATCH v3] watchdog: Add hrtimer-based pretimeout feature]

[Jiri Slaby <jirislaby@kernel.org>]

On 02. 09. 21, 16:05, Guenter Roeck wrote:
> On 9/1/21 11:55 PM, Jiri Slaby wrote:
>> On 03. 02. 21, 21:11, Curtis Klein wrote:
>>> This adds the option to use a hrtimer to generate a watchdog pretimeout
>>> event for hardware watchdogs that do not natively support watchdog
>>> pretimeouts.
>>>
>>> With this enabled, all watchdogs will appear to have pretimeout support
>>> in userspace. If no pretimeout value is set, there will be no change in
>>> the watchdog's behavior.
>>
>> Hi,
>>
>> on my Dell Latitude 7280, CONFIG_WATCHDOG_HRTIMER_PRETIMEOUT=y causes 
>> all reboot, kexec, suspend to panic. Disabling that option makes it 
>> all work again. Provided it happens very late in the process, I don't 
>> know how to grab some logs...
>>
>> Any ideas?
>>
> 
> AFAICS the timer does not stop on reboot. I think we'll need to augment 
> the code
> to do that.

No, it is stopped via device unregister -> watchdog_dev_unregister -> 
watchdog_cdev_unregister -> watchdog_hrtimer_pretimeout_stop.

But look:
watchdog_cdev_unregister
   -> wdd->wd_data = NULL;
   -> watchdog_hrtimer_pretimeout_stop
     -> hrtimer_cancel(&wdd->wd_data->pretimeout_timer);

The diff below obviously fixes the issue, but I don't know what the 
consequences are. The other possibility would be to pass wd_data 
directly to watchdog_hrtimer_pretimeout_stop.

I don't know how this can work on some machines (I verified it does).

--- a/drivers/watchdog/watchdog_dev.c
+++ b/drivers/watchdog/watchdog_dev.c
@@ -1096,6 +1096,8 @@ static void watchdog_cdev_unregister(struct 
watchdog_device *wdd)
                 watchdog_stop(wdd);
         }

+       watchdog_hrtimer_pretimeout_stop(wdd);
+
         mutex_lock(&wd_data->lock);
         wd_data->wdd = NULL;
         wdd->wd_data = NULL;
@@ -1103,7 +1105,6 @@ static void watchdog_cdev_unregister(struct 
watchdog_device *wdd)

         hrtimer_cancel(&wd_data->timer);
         kthread_cancel_work_sync(&wd_data->work);
-       watchdog_hrtimer_pretimeout_stop(wdd);

         put_device(&wd_data->dev);
  }

thanks,
-- 
js
suse labs