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

[Inki Dae]

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?

>