linux-kernel - Re: [PATCH] PM: Avoid false-positive warnings in dev_pm_domain

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Date:	Wed, 3 Feb 2016 14:18:30 +0100
From:	Ulf Hansson <ulf.hansson@...aro.org>
To:	"Rafael J. Wysocki" <rafael@...nel.org>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Tomeu Vizoso <tomeu.vizoso@...labora.com>,
	Kevin Hilman <khilman@...nel.org>
Subject: Re: [PATCH] PM: Avoid false-positive warnings in dev_pm_domain_set()

On 3 February 2016 at 13:08, Rafael J. Wysocki <rafael@...nel.org> wrote:
> On Wed, Feb 3, 2016 at 10:58 AM, Ulf Hansson <ulf.hansson@...aro.org> wrote:
>> On 30 January 2016 at 12:54, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
>>> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>>>
>>> There is a WARN_ON() in dev_pm_domain_set() that triggers on attempts
>>> to set the pm_domain pointer for devices with a driver bound.
>>>
>>> However, that WARN_ON() triggers on attempts to clear the pointer
>>> too and the test it uses is based on checking the device's
>>> p->knode_driver pointer which still is set when the device bus
>>> type's/driver's ->remove callback has been executed.  This
>>> leads to false-positive warnings when bus type code calls
>>> dev_pm_domain_set() to clear the pm_domain pointer after
>>> invoking the driver's ->remove() callback.
>>>
>>> To avoid those false-positives, make dev_pm_domain_set() check
>>> if the pointer passed to it is NULL and skip the warning in
>>> that case.
>>>
>>> Fixes: 989561de9b51 (PM / Domains: add setter for dev.pm_domain)
>>> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>>> ---
>>>  drivers/base/power/common.c |    2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> Index: linux-pm/drivers/base/power/common.c
>>> ===================================================================
>>> --- linux-pm.orig/drivers/base/power/common.c
>>> +++ linux-pm/drivers/base/power/common.c
>>> @@ -146,7 +146,7 @@ void dev_pm_domain_set(struct device *de
>>>         if (dev->pm_domain == pd)
>>>                 return;
>>>
>>> -       WARN(device_is_bound(dev),
>>> +       WARN(pd && device_is_bound(dev),
>>>              "PM domains can only be changed for unbound devices\n");
>>
>> Perhaps this information then becomes a bit misleading, as it's okay
>> to clear the pointer, but not assign it to a valid PM domain.
>
> Well, this is a "you're doing a wrong thing" warning and it does say
> what the wrong thing is.  Does it have to be more specific?  I don't
> think so.

Okay! I don't have a strong opinion.

Feel free to add:
Acked-by: Ulf Hansson <ulf.hansson@...aro.org>

Kind regards
Uffe