linux-kernel - Re: Gem GTT mmaps..

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Message-ID: <498CAD2F.5070806@shipmail.org>
Date:	Fri, 06 Feb 2009 22:35:43 +0100
From:	Thomas Hellström <thomas@...pmail.org>
To:	Jesse Barnes <jbarnes@...tuousgeek.org>
CC:	Eric Anholt <eric@...olt.net>,
	DRI <dri-devel@...ts.sourceforge.net>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: Gem GTT mmaps..

Jesse Barnes wrote:
> On Thursday, February 5, 2009 10:37 am Jesse Barnes wrote:
>   
>> So if we leave the lookup reference around from the GTT mapping ioctl, that
>> would take care of new mappings.  And if we added/removed references at VM
>> open/close time, we should be covered for fork.  But is it ok to add a new
>> unref in the finish ioctl for GTT mapped objects?  I don't think so,
>> because we don't know for sure if the caller was the one that created the
>> new fake offset (which would be one way of detecting whether it was GTT
>> mapped). Seems like we need a new unmap ioctl?  Or we could put the mapping
>> ref/unref in libdrm, where it would be tracked on a per-process basis...
>>     
>
> Ah but maybe we should just tear down the fake offset at unmap time; then we'd 
> be able to use it as an existence test for the mapping and get the 
> refcounting right.  The last thing I thought of was whether we'd be ok in a 
> map_gtt -> crash case.  I *think* the vm_close code will deal with that, if 
> we do a deref there?
>   
Yes, an mmap() is always paired with a vm_close(), and the vm_close() 
also happens in a crash situation.

/Thomas

> Thanks,
>   



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