linux-kernel - Re: [PATCH] drivers-core: nullify private pointer on device-release

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Message-ID: <ac3eb2510910010728v33e76f2ev751c20b3e454cf7a@mail.gmail.com>
Date:	Thu, 1 Oct 2009 16:28:31 +0200
From:	Kay Sievers <kay.sievers@...y.org>
To:	Greg KH <greg@...ah.com>
Cc:	Guennadi Liakhovetski <g.liakhovetski@....de>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drivers-core: nullify private pointer on device-release

On Thu, Oct 1, 2009 at 16:15, Greg KH <greg@...ah.com> wrote:
> On Thu, Oct 01, 2009 at 03:45:56PM +0200, Guennadi Liakhovetski wrote:

>> My problem case is the soc-camera framework. There device struct is
>> embedded into the video client object, which are kept as long as the
>> driver is loaded.
>
> struct device is a dynamic structure, it is supposed to be able to be
> freed when the last reference goes away.  Static struct device usage is
> wrong.  It sounds like the video client object code is incorrect, please
> fix it.

Exactly. If you keep your "object" around for forever, you must never
embed a struct device but only a pointer to one that is managed by the
core. Embedding a struct device defers lifetime management of the
enclosing object to the driver core reference counts.

You can not have both, you have to decide to let your objects be
managed by the driver core reference, or just point to a dynamic
driver core object. All driver core objects are always dynamic,
everything else just seem to work, but are not expected to work
reliably.

Thanks,
Kay
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