Re: [PATCH v3 3/3] drm/vgem: Keep a reference to the dmabuf when mmaped

[Daniel Vetter <daniel@ffwll.ch>]

On Fri, Sep 30, 2016 at 02:59:59PM +0100, Chris Wilson wrote:
> In order to keep the dmabuf alive whilst the mmap is, we need to hold a
> reference to the dmabuf and not the backing object. This is important as
> the dmabuf not only keeps the object alive, but also the device so that
> 
> 	dmabuf = vgem_create_dmabuf();
> 	ptr = mmap(... dmabuf ...);
> 	close(dmabuf);
> 
> persists across module-unload as well as device closure.

I don't see where we grab the ref to the dma-buf here instead of the
backing storage. And doesn't the exact same issue happen when you use dumb
mmap? Or maybe I'm just a bit confused about what's going on here ...
-Daniel

> 
> Testcase: igt/vgem_basic/unload
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Petri Latvala <petri.latvala@intel.com>
> ---
>  drivers/gpu/drm/vgem/vgem_drv.c | 17 +++--------------
>  1 file changed, 3 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/gpu/drm/vgem/vgem_drv.c b/drivers/gpu/drm/vgem/vgem_drv.c
> index f36c14729b55..74a83e41efa9 100644
> --- a/drivers/gpu/drm/vgem/vgem_drv.c
> +++ b/drivers/gpu/drm/vgem/vgem_drv.c
> @@ -198,7 +198,6 @@ static struct drm_ioctl_desc vgem_ioctls[] = {
>  
>  static int vgem_mmap(struct file *filp, struct vm_area_struct *vma)
>  {
> -	unsigned long flags = vma->vm_flags;
>  	int ret;
>  
>  	ret = drm_gem_mmap(filp, vma);
> @@ -208,7 +207,7 @@ static int vgem_mmap(struct file *filp, struct vm_area_struct *vma)
>  	/* Keep the WC mmaping set by drm_gem_mmap() but our pages
>  	 * are ordinary and not special.
>  	 */
> -	vma->vm_flags = flags | VM_DONTEXPAND | VM_DONTDUMP;
> +	vma->vm_flags &= ~(VM_IO | VM_PFNMAP);
>  	return 0;
>  }
>  
> @@ -281,21 +280,11 @@ static int vgem_prime_mmap(struct drm_gem_object *obj,
>  {
>  	int ret;
>  
> -	if (obj->size < vma->vm_end - vma->vm_start)
> -		return -EINVAL;
> -
> -	if (!obj->filp)
> -		return -ENODEV;
> -
> -	ret = obj->filp->f_op->mmap(obj->filp, vma);
> +	ret = drm_gem_mmap_obj(obj, obj->size, vma);
>  	if (ret)
>  		return ret;
>  
> -	fput(vma->vm_file);
> -	vma->vm_file = get_file(obj->filp);
> -	vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP;
> -	vma->vm_page_prot = pgprot_writecombine(vm_get_page_prot(vma->vm_flags));
> -
> +	vma->vm_flags &= ~(VM_IO | VM_PFNMAP);
>  	return 0;
>  }
>  
> -- 
> 2.9.3
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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