Re: [PATCH 9/9] drm/shmem-helpers: Simplify dma-buf importing

[Thomas Zimmermann <tzimmermann@suse.de>]

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Hi

Am 14.05.20 um 14:55 schrieb Daniel Vetter:
> On Thu, May 14, 2020 at 09:44:02AM +0200, Thomas Zimmermann wrote:
>> Hi
>>
>> Am 11.05.20 um 11:35 schrieb Daniel Vetter:
>>> - Ditch the ->pages array
>>> - Make it a private gem bo, which means no shmem object, which means
>>>   fireworks if anyone calls drm_gem_object_get_pages. But we've just
>>>   made sure that's all covered.
>>>
>>> Cc: Gerd Hoffmann <kraxel@redhat.com>
>>> Cc: Rob Herring <robh@kernel.org>
>>> Cc: Noralf Trønnes <noralf@tronnes.org>
>>> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
>>> ---
>>>  drivers/gpu/drm/drm_gem_shmem_helper.c | 59 ++++++++++----------------
>>>  1 file changed, 23 insertions(+), 36 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
>>> index f7011338813e..8c7d4f422b7b 100644
>>> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
>>> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
>>> @@ -35,22 +35,12 @@ static const struct drm_gem_object_funcs drm_gem_shmem_funcs = {
>>>  	.mmap = drm_gem_shmem_mmap,
>>>  };
>>>  
>>> -/**
>>> - * drm_gem_shmem_create - Allocate an object with the given size
>>> - * @dev: DRM device
>>> - * @size: Size of the object to allocate
>>> - *
>>> - * This function creates a shmem GEM object.
>>> - *
>>> - * Returns:
>>> - * A struct drm_gem_shmem_object * on success or an ERR_PTR()-encoded negative
>>> - * error code on failure.
>>> - */
>>> -struct drm_gem_shmem_object *drm_gem_shmem_create(struct drm_device *dev, size_t size)
>>> +static struct drm_gem_shmem_object *
>>> +__drm_gem_shmem_create(struct drm_device *dev, size_t size, bool private)
>>>  {
>>>  	struct drm_gem_shmem_object *shmem;
>>>  	struct drm_gem_object *obj;
>>> -	int ret;
>>> +	int ret = 0;
>>>  
>>>  	size = PAGE_ALIGN(size);
>>>  
>>> @@ -64,7 +54,10 @@ struct drm_gem_shmem_object *drm_gem_shmem_create(struct drm_device *dev, size_t
>>>  	if (!obj->funcs)
>>>  		obj->funcs = &drm_gem_shmem_funcs;
>>>  
>>> -	ret = drm_gem_object_init(dev, obj, size);
>>> +	if (private)
>>> +		drm_gem_private_object_init(dev, obj, size);
>>> +	else
>>> +		ret = drm_gem_object_init(dev, obj, size);
>>>  	if (ret)
>>>  		goto err_free;
>>>  
>>> @@ -96,6 +89,21 @@ struct drm_gem_shmem_object *drm_gem_shmem_create(struct drm_device *dev, size_t
>>>  
>>>  	return ERR_PTR(ret);
>>>  }
>>> +/**
>>> + * drm_gem_shmem_create - Allocate an object with the given size
>>> + * @dev: DRM device
>>> + * @size: Size of the object to allocate
>>> + *
>>> + * This function creates a shmem GEM object.
>>> + *
>>> + * Returns:
>>> + * A struct drm_gem_shmem_object * on success or an ERR_PTR()-encoded negative
>>> + * error code on failure.
>>> + */
>>> +struct drm_gem_shmem_object *drm_gem_shmem_create(struct drm_device *dev, size_t size)
>>> +{
>>> +	return __drm_gem_shmem_create(dev, size, false);
>>> +}
>>>  EXPORT_SYMBOL_GPL(drm_gem_shmem_create);
>>>  
>>>  /**
>>> @@ -115,7 +123,6 @@ void drm_gem_shmem_free_object(struct drm_gem_object *obj)
>>>  	if (obj->import_attach) {
>>>  		shmem->pages_use_count--;
>>>  		drm_prime_gem_destroy(obj, shmem->sgt);
>>> -		kvfree(shmem->pages);
>>>  	} else {
>>>  		if (shmem->sgt) {
>>>  			dma_unmap_sg(obj->dev->dev, shmem->sgt->sgl,
>>> @@ -371,7 +378,7 @@ drm_gem_shmem_create_with_handle(struct drm_file *file_priv,
>>>  	struct drm_gem_shmem_object *shmem;
>>>  	int ret;
>>>  
>>> -	shmem = drm_gem_shmem_create(dev, size);
>>> +	shmem = __drm_gem_shmem_create(dev, size, true);
>>>  	if (IS_ERR(shmem))
>>>  		return shmem;
>>>  
>>> @@ -695,36 +702,16 @@ drm_gem_shmem_prime_import_sg_table(struct drm_device *dev,
>>>  				    struct sg_table *sgt)
>>>  {
>>>  	size_t size = PAGE_ALIGN(attach->dmabuf->size);
>>> -	size_t npages = size >> PAGE_SHIFT;
>>>  	struct drm_gem_shmem_object *shmem;
>>> -	int ret;
>>>  
>>>  	shmem = drm_gem_shmem_create(dev, size);
>>>  	if (IS_ERR(shmem))
>>>  		return ERR_CAST(shmem);
>>>  
>>> -	shmem->pages = kvmalloc_array(npages, sizeof(struct page *), GFP_KERNEL);
>>> -	if (!shmem->pages) {
>>> -		ret = -ENOMEM;
>>> -		goto err_free_gem;
>>> -	}
>>> -
>>> -	ret = drm_prime_sg_to_page_addr_arrays(sgt, shmem->pages, NULL, npages);
>>> -	if (ret < 0)
>>> -		goto err_free_array;
>>> -
>>>  	shmem->sgt = sgt;
>>> -	shmem->pages_use_count = 1; /* Permanently pinned from our point of view */
>>
>> This counter protected drm_gem_shmem_get_pages() from being executed on
>> imported buffers. I guess that previous patches sorted out all the
>> instances where this could occur. If so, the current patch looks
>> correct. I'm not sure, if the overall code is really better than what we
>> have ATM, but anyway
> 
> The goal was to clearly sort these cases out, iirc we had callers of
> get_pages doing the wrong thing, but I tried to review them all. Some got
> removed while this series was hanging around in my tree somewhere.
> 
> What I wanted to do in the end is replace all mutex_lock with
> dma_resv_lock, which now should be doable. Except I need to audit all the
> drivers, and some want _locked variant since they are already holding the
> lock. That's roughly the point where I gave up on this eandeavour, at
> least for now.
> 
> But if we'd get there then all the various helpers we have (cma, shmem,
> vram) would more or less properly use dma_resv_lock as their protectiong
> concept. That's kinda neat since with the dynamic dma-buf stuff
> dma_resv_lock really becomes _the_ buffer lock for drivers, so some
> motivation to move towards that.
> 
> Anyway if you don't feel like this is all that useful without the
> dma_resv_lock work on top, I guess I can merge up to the doc patch and
> leave the others out. Not sure myself, thoughts?

Don't get me wrong, it's useful. The dma-buf support is just always a
bit special and bolted-on in all memory managers.

Please go ahead and merge it if you like. The clean separation of
dma-buf calls is better than what I did in my shmem patches. I'll rebase
my stuff on top of whatever you end up merging.

Best regards
Thomas

> 
> Thanks for taking a look.
> -Daniel
> 
>>
>> Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
>>
>>>  
>>>  	DRM_DEBUG_PRIME("size = %zu\n", size);
>>>  
>>>  	return &shmem->base;
>>> -
>>> -err_free_array:
>>> -	kvfree(shmem->pages);
>>> -err_free_gem:
>>> -	drm_gem_object_put_unlocked(&shmem->base);
>>> -
>>> -	return ERR_PTR(ret);
>>>  }
>>>  EXPORT_SYMBOL_GPL(drm_gem_shmem_prime_import_sg_table);
>>>
>>
>> -- 
>> Thomas Zimmermann
>> Graphics Driver Developer
>> SUSE Software Solutions Germany GmbH
>> Maxfeldstr. 5, 90409 Nürnberg, Germany
>> (HRB 36809, AG Nürnberg)
>> Geschäftsführer: Felix Imendörffer
>>
> 
> 
> 
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer


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