[Intel-gfx] [PATCH 6/9] drm/shmem-helpers: Don't call get/put_pages on imported dma-buf in vmap

[Thomas Zimmermann]

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.
> 
> Cc: Gerd Hoffmann <kraxel at redhat.com>
> Cc: Rob Herring <robh at kernel.org>
> Cc: Noralf Trønnes <noralf at tronnes.org>
> Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
> ---
>  drivers/gpu/drm/drm_gem_shmem_helper.c | 17 +++++++++--------
>  1 file changed, 9 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> index 2a70159d50ef..b9cba5cc61c3 100644
> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> @@ -252,32 +252,33 @@ static void *drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem)
>  	if (shmem->vmap_use_count++ > 0)
>  		return shmem->vaddr;
>  
> -	ret = drm_gem_shmem_get_pages(shmem);
> -	if (ret)
> -		goto err_zero_use;
> -
>  	if (obj->import_attach) {
>  		shmem->vaddr = dma_buf_vmap(obj->import_attach->dmabuf);
>  	} else {
>  		pgprot_t prot = PAGE_KERNEL;
>  
> +		ret = drm_gem_shmem_get_pages(shmem);
> +		if (ret)
> +			goto err;
> +
>  		if (!shmem->map_cached)
>  			prot = pgprot_writecombine(prot);
>  		shmem->vaddr = vmap(shmem->pages, obj->size >> PAGE_SHIFT,
>  				    VM_MAP, prot);
> +
> +		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;
>  	}
>  
>  	return shmem->vaddr;
>  
> -err_put_pages:
> -	drm_gem_shmem_put_pages(shmem);

I found the new code to be less readable. Maybe keep the error rollback
as-is and protect _put_pages() with if (!import_attach).

In any case

Acked-by: Thomas Zimmermann <tzimmermann at suse.de>

> -err_zero_use:
> +err:
>  	shmem->vmap_use_count = 0;
>  
>  	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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