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

[Inki Dae]

On 2015년 08월 17일 17:17, Joonyoung Shim wrote:
> 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 at 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.

Hmm... It's not that the mmap offset can be re-used or not. It's that
the mmap offset should be released or not when mmap failed. As your
original comment, the call of drm_gem_free_mmap_offset() is unnecessary
if mmap offset is created when gem creation because the mmap offset is
removed by drm_gem_object_release() when gem is destroyed - gem should
also be released when mmap failed.

Ok, let's create mmap offset at gem creation and remove it gem
releasing. Will merge these two patches.

Thanks,
Inki Dae

>