Re: [PATCH] PM: Avoid false-positive warnings in dev_pm_domain_set()

[Rafael J. Wysocki]

On Wed, Feb 3, 2016 at 10:58 AM, Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote:
> On 30 January 2016 at 12:54, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote:
>> From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
>>
>> 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@xxxxxxxxx>
>> ---
>>  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.

Thanks,
Rafael