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Date: Mon, 27 May 2013 17:23:00 +0200
From: Maarten Lankhorst <maarten.lankhorst@canonical.com>
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To: Inki Dae <inki.dae@samsung.com>
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Subject: Re: Introduce a new helper framework for buffer synchronization
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Hey,

Op 27-05-13 12:38, Inki Dae schreef:
> Hi all,
>
> I have been removed previous branch and added new one with more cleanup.
> This time, the fence helper doesn't include user side interfaces and cache
> operation relevant codes anymore because not only we are not sure that
> coupling those two things, synchronizing caches and buffer access between
> CPU and CPU, CPU and DMA, and DMA and DMA with fences, in kernel side is a
> good idea yet but also existing codes for user side have problems with badly
> behaved or crashing userspace. So this could be more discussed later.
>
> The below is a new branch,
> 	
> https://git.kernel.org/cgit/linux/kernel/git/daeinki/drm-exynos.git/?h=dma-f
> ence-helper
>
> And fence helper codes,
> 	
> https://git.kernel.org/cgit/linux/kernel/git/daeinki/drm-exynos.git/commit/?
> h=dma-fence-helper&id=adcbc0fe7e285ce866e5816e5e21443dcce01005
>
> And example codes for device driver,
> 	
> https://git.kernel.org/cgit/linux/kernel/git/daeinki/drm-exynos.git/commit/?
> h=dma-fence-helper&id=d2ce7af23835789602a99d0ccef1f53cdd5caaae
>
> I think the time is not yet ripe for RFC posting: maybe existing dma fence
> and reservation need more review and addition work. So I'd glad for somebody
> giving other opinions and advices in advance before RFC posting.
>
NAK.

For examples for how to handle locking properly, see Documentation/ww-mutex-design.txt in my recent tree.
I could list what I believe is wrong with your implementation, but real problem is that the approach you're taking is wrong.

~Maarten