linux-kernel - Re: [PATCH] of: Deep-copy names of platform devices

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Date:	Fri, 15 Aug 2014 12:01:49 +0100
From:	Grant Likely <grant.likely@...aro.org>
To:	Stephen Boyd <sboyd@...eaurora.org>,
	Stepan Moskovchenko <stepanm@...eaurora.org>
Cc:	Rob Herring <robh+dt@...nel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>
Subject: Re: [PATCH] of: Deep-copy names of platform devices

On Fri, Aug 15, 2014 at 11:52 AM, Grant Likely <grant.likely@...aro.org> wrote:
> On Fri, Aug 15, 2014 at 11:45 AM, Grant Likely <grant.likely@...aro.org> wrote:
>> On Tue, 12 Aug 2014 18:46:36 -0700, Stephen Boyd <sboyd@...eaurora.org> wrote:
>>> On 08/12/14 17:57, Stepan Moskovchenko wrote:
>>> > diff --git a/drivers/of/device.c b/drivers/of/device.c
>>> > index f685e55..3e116f6 100644
>>> > --- a/drivers/of/device.c
>>> > +++ b/drivers/of/device.c
>>> > @@ -54,7 +54,7 @@ int of_device_add(struct platform_device *ofdev)
>>> >
>>> >     /* name and id have to be set so that the platform bus doesn't get
>>> >      * confused on matching */
>>> > -   ofdev->name = dev_name(&ofdev->dev);
>>> > +   ofdev->name = kstrdup(dev_name(&ofdev->dev), GFP_KERNEL);
>>> >     ofdev->id = -1;
>>> >
>>> >     /* device_add will assume that this device is on the same node as
>>> > @@ -76,6 +76,7 @@ EXPORT_SYMBOL(of_device_register);
>>> >  void of_device_unregister(struct platform_device *ofdev)
>>> >  {
>>> >     device_unregister(&ofdev->dev);
>>> > +   kfree(ofdev->name);
>>>
>>> This probably ought to be swapped because we don't know if ofdev isn't
>>> pointing to freed memory after device_unregister().
>>
>> Actually, the only safe place to free the memory is inside the
>> platform_device release function. platform_device_release() in
>> drivers/base/platform.c. Unfortunately there isn't a good way from that
>> function to figure out if the name has been allocated the 'OF' way.
>>
>> It is not safe to free it here because there could still be references
>> to the platform_device after device_unregister exits.
>
> We could fix the problem by making platform_device_alloc() also do a
> kstrdup() when assigning the name. Then the release function can
> unconditionally free the name field. Care to try that out?

I don't know how well received that will be though. The vast majority
of non-OF callers of platform_device_alloc() pass in a static string
that will never disappear.

Another possible solutions: Override the release function for platform
devices allocated by of_device_alloc() to free the name field.

g.
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