linux-kernel - Re: [RFC 1/2] core: Add generic object registry implementation

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Message-ID: <20141106161321.GB14873@ulmo.nvidia.com>
Date:	Thu, 6 Nov 2014 17:13:24 +0100
From:	Thierry Reding <thierry.reding@...il.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Daniel Vetter <daniel.vetter@...ll.ch>,
	David Herrmann <dh.herrmann@...il.com>,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC 1/2] core: Add generic object registry implementation

On Thu, Nov 06, 2014 at 11:25:32AM +0100, Thierry Reding wrote:
> On Wed, Nov 05, 2014 at 06:18:15PM -0800, Greg Kroah-Hartman wrote:
[...]
> > Sure, document it better if you want, but I think something needs to be
> > done differently if at all possible.
> 
> try_module_get() is the only way I know of that ensures that the code of
> a module stays around. Everytime we give out a new reference to a record
> we also need to increment the module reference count accordingly to make
> sure the underlying code doesn't go away all of a sudden.
> 
> I guess that's not entirely accurate. The module reference count doesn't
> have to be increment for every record reference, it only needs to track
> each record. So the try_module_get() and module_put() could move into
> registry_add() and registry_get(), respectively. But the ->owner field
> would still be in the record structure.

On further thought I don't think this will work either. Given that the
record can be removed from the registry while somebody else still has a
reference to it, the module owning the record must stay around as long
as there's a reference to the record.

Maybe the module reference count needs to be incremented when the record
is initialized and decremented when the record is released.

Thierry

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