linux-kernel - Re: [PATCH] device property: Track owner device of device property

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Message-ID: <fcde8be2-e19b-901c-b8fe-8dc54d1e847d@linux.intel.com>
Date:   Tue, 24 Oct 2017 16:41:21 +0300
From:   Jarkko Nikula <jarkko.nikula@...ux.intel.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Lukas Wunner <lukas@...ner.de>, stable@...r.kernel.org
Subject: Re: [PATCH] device property: Track owner device of device property

On 10/20/2017 05:34 PM, Greg Kroah-Hartman wrote:
>> @@ -938,6 +940,7 @@ int device_add_properties(struct device *dev,
>>   
>>   	p->fwnode.ops = &pset_fwnode_ops;
>>   	set_secondary_fwnode(dev, &p->fwnode);
>> +	p->dev = dev;
> 
> Don't you also need to increment the reference counter here?  Or how is
> it assured that it will not go away?
> 
I need to scratch my head on this. It sounds more robust to track 
references and remove properties when last reference is dropped in 
device_remove_properties(). What I don't know are properties be expected 
to be copied and be usable for another device for instance by 
ACPI_COMPANION_SET().

I can figure out case where properties are added to one device, another 
device gets reference to them via ACPI_COMPANION_SET() and properties 
get freed when the first device is removed. But should the second device 
be able to use those properties at first place?

Rafael: What's you opinion: should there be reference counting for 
device properties? Initial increment in device_add_properties(), other 
around ACPI_COMPANION_SET()/set_primary_fwnode() and decrementing in 
device_remove_properties().

-- 
Jarkko