Re: [PATCH 5/9] drm/udl: Don't call get/put_pages on imported dma-buf

[Thomas Zimmermann <tzimmermann@suse.de>]

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Hi

Am 11.05.20 um 11:35 schrieb Daniel Vetter:
> There's no direct harm, because for the shmem helpers these are noops
> on imported buffers. The trouble is in the locks these take - I want
> to change dma_buf_vmap locking, and so need to make sure that we only
> ever take certain locks on one side of the dma-buf interface: Either
> for exporters, or for importers.
> 
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> Cc: Dave Airlie <airlied@redhat.com>
> Cc: Sean Paul <sean@poorly.run>
> Cc: Gerd Hoffmann <kraxel@redhat.com>
> Cc: Thomas Zimmermann <tzimmermann@suse.de>
> Cc: Alex Deucher <alexander.deucher@amd.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Sam Ravnborg <sam@ravnborg.org>
> ---
>  drivers/gpu/drm/udl/udl_gem.c | 22 ++++++++++++----------
>  1 file changed, 12 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/gpu/drm/udl/udl_gem.c b/drivers/gpu/drm/udl/udl_gem.c
> index b6e26f98aa0a..c68d3e265329 100644
> --- a/drivers/gpu/drm/udl/udl_gem.c
> +++ b/drivers/gpu/drm/udl/udl_gem.c
> @@ -46,29 +46,31 @@ static void *udl_gem_object_vmap(struct drm_gem_object *obj)

It's still not clear to me why this function exists in the first place.
It's the same code as the default implementation, except that it doesn't
support cached mappings.

I don't see why udl is special. I'd suggest to try to use the original
shmem function and remove this one. Same for the mmap code.

Best regards
Thomas

>  	if (shmem->vmap_use_count++ > 0)
>  		goto out;
>  
> -	ret = drm_gem_shmem_get_pages(shmem);
> -	if (ret)
> -		goto err_zero_use;
> -
> -	if (obj->import_attach)
> +	if (obj->import_attach) {
>  		shmem->vaddr = dma_buf_vmap(obj->import_attach->dmabuf);
> -	else
> +	} else {
> +		ret = drm_gem_shmem_get_pages(shmem);
> +		if (ret)
> +			goto err;
> +
>  		shmem->vaddr = vmap(shmem->pages, obj->size >> PAGE_SHIFT,
>  				    VM_MAP, PAGE_KERNEL);
>  
> +		if (!shmem->vaddr)
> +			drm_gem_shmem_put_pages(shmem);
> +	}
> +
>  	if (!shmem->vaddr) {
>  		DRM_DEBUG_KMS("Failed to vmap pages\n");
>  		ret = -ENOMEM;
> -		goto err_put_pages;
> +		goto err;
>  	}
>  
>  out:
>  	mutex_unlock(&shmem->vmap_lock);
>  	return shmem->vaddr;
>  
> -err_put_pages:
> -	drm_gem_shmem_put_pages(shmem);
> -err_zero_use:
> +err:
>  	shmem->vmap_use_count = 0;
>  	mutex_unlock(&shmem->vmap_lock);
>  	return ERR_PTR(ret);
> 

-- 
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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