Re: [PATCH 09/14] drm/exynos: remove call to drm_gem_free_mmap_offset()

[Joonyoung Shim <jy0922.shim@samsung.com>]

On 08/17/2015 04:52 PM, Inki Dae wrote:
> On 2015년 08월 17일 14:29, Joonyoung Shim wrote:
>> On 08/16/2015 02:07 PM, Inki Dae wrote:
>>> On 2015년 07월 28일 17:53, Joonyoung Shim wrote:
>>>> The drm_gem_object_release() function already performs this cleanup,
>>>> so there is no reason to do it explicitly.
>>>>
>>>> Signed-off-by: Joonyoung Shim <jy0922.shim@samsung.com>
>>>> ---
>>>>  drivers/gpu/drm/exynos/exynos_drm_gem.c | 3 ---
>>>>  1 file changed, 3 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/exynos/exynos_drm_gem.c b/drivers/gpu/drm/exynos/exynos_drm_gem.c
>>>> index c76aa8a..ab7d029 100644
>>>> --- a/drivers/gpu/drm/exynos/exynos_drm_gem.c
>>>> +++ b/drivers/gpu/drm/exynos/exynos_drm_gem.c
>>>> @@ -100,8 +100,6 @@ out:
>>>>  	exynos_drm_fini_buf(obj->dev, buf);
>>>>  	exynos_gem_obj->buffer = NULL;
>>>>  
>>>> -	drm_gem_free_mmap_offset(obj);
>>>> -
>>>>  	/* release file pointer to gem object. */
>>>>  	drm_gem_object_release(obj);
>>>>  
>>>> @@ -600,7 +598,6 @@ int exynos_drm_gem_mmap(struct file *filp, struct vm_area_struct *vma)
>>>>  
>>>>  err_close_vm:
>>>>  	drm_gem_vm_close(vma);
>>>> -	drm_gem_free_mmap_offset(obj);
>>>
>>> Without previous patch, drm_gem_free_mmap_offset is required. I guess
>>> the reason you removed above line is that you thought
>>> drm_gem_object_release function would be called by drm_gem_vm_close
>>> function which drops a reference of the gem object.
>>>
>>> However, drm_gem_vm_close should be a pair with drm_gem_vm_open
>>> function. These will be called whenever a process opens or closes the
>>> VMA. So the reference count of the gem object had already been taken by
>>> open operation when a new reference to the VMA had been created.
>>>
>>
>> This changes is not related with drm_gem_vm_close and prior patch. Why
>> should free mmap offset when mmap operation is failed? The mmap offset
>> can be used repeatedly.
> 
> Isn't vm space of vm manager still used even if any user-space process
> doesn't use the region? And if mmap is failed, then the user-space
> process will be terminated. Do you think it can be re-tried? However,
> mmap system call never return -EAGAIN. Is it reasonable to you? I cannot
> understand how the mmap offset can be re-used. So can you show me some
> example?
> 

Currently, mmap offset of exynos-drm gem is made by                 
DRM_IOCTL_MODE_MAP_DUMB ioctl and mmap() ioctl just uses the mmap     
offset. User will use same mmap offset about same gem. It's why mmap
offset made by DRM_IOCTL_MODE_MAP_DUMB ioctl is unnecessary, it's just
enough to make mmap offset from when gem is create. You can get a
reference from drm_gem_cma_helper.c file.
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