linux-kernel - Re: [PATCH] dma-buf: add reference counting for exporter module

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Date:	Wed, 08 Aug 2012 15:53:10 +0200
From:	Tomasz Stanislawski <t.stanislaws@...sung.com>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:	dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	devel@...verdev.osuosl.org, Pawel Osciak <pawel@...iak.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jerome Glisse <jglisse@...hat.com>,
	Vinod Koul <vinod.koul@...el.com>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Rob Landley <rob@...dley.net>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Alex Deucher <alexander.deucher@....com>,
	Rob Clark <rob@...com>,
	Dan Williams <dan.j.williams@...el.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	linux-media@...r.kernel.org
Subject: Re: [PATCH] dma-buf: add reference counting for exporter module

Hi Laurent,

On 08/08/2012 03:35 PM, Laurent Pinchart wrote:
> Hi Tomasz,
> 
> Thanks for the patch.
> 
> On Wednesday 08 August 2012 12:17:41 Tomasz Stanislawski wrote:
>> This patch adds reference counting on a module that exports dma-buf and
>> implements its operations. This prevents the module from being unloaded
>> while DMABUF file is in use.
>>
>> Signed-off-by: Tomasz Stanislawski <t.stanislaws@...sung.com>
>> ---
>>  Documentation/dma-buf-sharing.txt          |    3 ++-
>>  drivers/base/dma-buf.c                     |   10 +++++++++-
>>  drivers/gpu/drm/exynos/exynos_drm_dmabuf.c |    1 +
>>  drivers/gpu/drm/i915/i915_gem_dmabuf.c     |    1 +
>>  drivers/gpu/drm/nouveau/nouveau_prime.c    |    1 +
>>  drivers/gpu/drm/radeon/radeon_prime.c      |    1 +
>>  drivers/staging/omapdrm/omap_gem_dmabuf.c  |    1 +
>>  include/linux/dma-buf.h                    |    2 ++
>>  8 files changed, 18 insertions(+), 2 deletions(-)
>>
[snip]

>> @@ -96,6 +98,7 @@ struct dma_buf *dma_buf_export(void *priv, const struct
>> dma_buf_ops *ops, struct file *file;
>>
>>  	if (WARN_ON(!priv || !ops
>> +			  || !ops->owner

Thank you for spotting this.
I didn'y know that try_get_module returned true is module was NULL.

BTW. Is it worth to add ".owner = THIS_MODULE," to all dma_buf
exporters in this patch?

Regards,
Tomasz Stanislawski

> 
> THIS_MODULE is defined as ((struct module *)0) when the driver is built-in, 
> this check should thus be removed.
> 
>>  			  || !ops->map_dma_buf
>>  			  || !ops->unmap_dma_buf
>>  			  || !ops->release
>>

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