linux-kernel - Re: [PATCH v2 2/8] watchdog: Introduce hardware maximum timeout in watchdog core

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Message-ID: <55CFC974.9070308@roeck-us.net>
Date:	Sat, 15 Aug 2015 16:21:24 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
CC:	linux-watchdog@...r.kernel.org, Wim Van Sebroeck <wim@...ana.be>,
	linux-kernel@...r.kernel.org,
	Timo Kokkonen <timo.kokkonen@...code.fi>,
	linux-doc@...r.kernel.org, Jonathan Corbet <corbet@....net>
Subject: Re: [PATCH v2 2/8] watchdog: Introduce hardware maximum timeout in
 watchdog core

On 08/14/2015 04:23 AM, Uwe Kleine-König wrote:
> Hello Guenter,
>
> On Fri, Aug 07, 2015 at 10:02:41PM -0700, Guenter Roeck wrote:
>> [...]
>> @@ -61,26 +135,27 @@ static struct watchdog_device *old_wdd;
>>
>>   static int watchdog_ping(struct watchdog_device *wdd)
>>   {
>> -	int err = 0;
>> +	int err;
>>
>>   	mutex_lock(&wdd->lock);
>> +	err = _watchdog_ping(wdd);
>> +	wdd->last_keepalive = jiffies;
>> +	watchdog_update_worker(wdd, false, false);
>> +	mutex_unlock(&wdd->lock);
>>
>> -	if (test_bit(WDOG_UNREGISTERED, &wdd->status)) {
>> -		err = -ENODEV;
>> -		goto out_ping;
>> -	}
>> +	return err;
>> +}
>>
>> -	if (!watchdog_active(wdd))
>> -		goto out_ping;
>> +static void watchdog_ping_work(struct work_struct *work)
>> +{
>> +	struct watchdog_device *wdd;
>>
>> -	if (wdd->ops->ping)
>> -		err = wdd->ops->ping(wdd);	/* ping the watchdog */
>> -	else
>> -		err = wdd->ops->start(wdd);	/* restart watchdog */
>> +	wdd = container_of(to_delayed_work(work), struct watchdog_device, work);
>>
>> -out_ping:
>> +	mutex_lock(&wdd->lock);
>> +	_watchdog_ping(wdd);
>> +	watchdog_update_worker(wdd, false, false);
>>   	mutex_unlock(&wdd->lock);
>> -	return err;
>>   }
>>
>>   /*
>> @@ -107,8 +182,11 @@ static int watchdog_start(struct watchdog_device *wdd)
>>   		goto out_start;
>>
>>   	err = wdd->ops->start(wdd);
>> -	if (err == 0)
>> +	if (err == 0) {
>>   		set_bit(WDOG_ACTIVE, &wdd->status);
>> +		wdd->last_keepalive = jiffies;
>> +		watchdog_update_worker(wdd, false, false);
>> +	}
>>
>>   out_start:
>>   	mutex_unlock(&wdd->lock);
>> @@ -146,8 +224,10 @@ static int watchdog_stop(struct watchdog_device *wdd)
>>   	}
>>
>>   	err = wdd->ops->stop(wdd);
>> -	if (err == 0)
>> +	if (err == 0) {
>>   		clear_bit(WDOG_ACTIVE, &wdd->status);
>> +		watchdog_update_worker(wdd, true, false);
>> +	}
>>
>>   out_stop:
>>   	mutex_unlock(&wdd->lock);
>> @@ -211,6 +291,8 @@ static int watchdog_set_timeout(struct watchdog_device *wdd,
>>
>>   	err = wdd->ops->set_timeout(wdd, timeout);
>>
>> +	watchdog_update_worker(wdd, true, false);
>
> I still try to wrap my head around this function. You pass cancel=true
> for stop and set_timeout to ensure that the worker doesn't continue to
> run. That's fine.
>
> For watchdog_start you pass cancel=false. I guess the background is that
> after one of the next patches the worker might already run for handling
> the watchdog being unstoppable. Maybe it's easier to grasp the logic if
> you don't try to be too clever here: stop the worker on start
> unconditionally and possibly restart it if the hardware needs extra
> poking to fulfil the timeout set?
>
I thought it would reduce the amount of code, and I thought it would be
more confusing and complicated to first call cancel the worker followed
by a (conditional) start. No strong opinion, though; I'll be happy to
make that change in exchange for a Reviewed-by:.


>> +	if (!watchdog_wq)
>> +		return -ENODEV;
>> +
>> +	INIT_DELAYED_WORK(&wdd->work, watchdog_ping_work);
>> +
>> +	if (!wdd->max_hw_timeout_ms)
>> +		wdd->max_hw_timeout_ms = wdd->max_timeout * 1000;
>
> With this (and assuming wdd->max_timeout > 0) the check for
> max_hw_timeout_ms != 0 is not necessary, is it?
>
With the logical change I am making, to ignore max_timeout if max_hw_timeout_ms
is configured, it is indeed no longer necessary (nor desirable).

>> +
>>   	if (wdd->id == 0) {
>>   		old_wdd = wdd;
>>   		watchdog_miscdev.parent = wdd->parent;
>> [...]
>> @@ -585,9 +680,21 @@ int watchdog_dev_unregister(struct watchdog_device *wdd)
>>
>>   int __init watchdog_dev_init(void)
>>   {
>> -	int err = alloc_chrdev_region(&watchdog_devt, 0, MAX_DOGS, "watchdog");
>> +	int err;
>> +
>> +	watchdog_wq = alloc_workqueue("watchdogd",
>> +				      WQ_HIGHPRI | WQ_MEM_RECLAIM, 0);
>> +	if (!watchdog_wq) {
>> +		pr_err("Failed to create watchdog workqueue\n");
>> +		err = -ENOMEM;
>> +		goto abort;
>
> Why not return -ENOMEM directly?
>
No idea. Changed.

Thanks,
Guenter

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