[Mesa-dev] [PATCH] intel: Track known prime buffers for re-use

[Daniel Vetter]

On Mon, Nov 25, 2013 at 01:22:41PM -0800, Keith Packard wrote:
> If the application sends us a file descriptor pointing at a prime
> buffer that we've already got, we have to re-use the same bo_gem
> structure or chaos will result.
> 
> Track the set of all known prime objects and look to see if the kernel
> has returned one of those for a new file descriptor.
> 
> Also checks for prime buffers in the flink case.
> 
> Signed-off-by: Keith Packard <keithp at keithp.com>
> ---
>  intel/intel_bufmgr_gem.c | 50 +++++++++++++++++++++++++++++++++++++++++-------
>  1 file changed, 43 insertions(+), 7 deletions(-)
> 
> diff --git a/intel/intel_bufmgr_gem.c b/intel/intel_bufmgr_gem.c
> index df6fcec..2b7fe07 100644
> --- a/intel/intel_bufmgr_gem.c
> +++ b/intel/intel_bufmgr_gem.c
> @@ -149,6 +149,8 @@ struct _drm_intel_bo_gem {
>  
>  	/**
>  	 * Kenel-assigned global name for this object
> +         *
> +         * List contains both flink named and prime fd'd objects
>  	 */
>  	unsigned int global_name;
>  	drmMMListHead name_list;
> @@ -862,10 +864,6 @@ drm_intel_bo_gem_create_from_name(drm_intel_bufmgr *bufmgr,
>  		}
>  	}
>  
> -	bo_gem = calloc(1, sizeof(*bo_gem));
> -	if (!bo_gem)
> -		return NULL;
> -
>  	VG_CLEAR(open_arg);
>  	open_arg.name = handle;
>  	ret = drmIoctl(bufmgr_gem->fd,
> @@ -874,9 +872,26 @@ drm_intel_bo_gem_create_from_name(drm_intel_bufmgr *bufmgr,
>  	if (ret != 0) {
>  		DBG("Couldn't reference %s handle 0x%08x: %s\n",
>  		    name, handle, strerror(errno));
> -		free(bo_gem);
>  		return NULL;
>  	}
> +        /* Now see if someone has used a prime handle to get this
> +         * object from the kernel before by looking through the list
> +         * again for a matching gem_handle
> +         */
> +	for (list = bufmgr_gem->named.next;
> +	     list != &bufmgr_gem->named;
> +	     list = list->next) {
> +		bo_gem = DRMLISTENTRY(drm_intel_bo_gem, list, name_list);
> +		if (bo_gem->gem_handle == open_arg.handle) {
> +			drm_intel_gem_bo_reference(&bo_gem->bo);
> +			return &bo_gem->bo;
> +		}
> +	}

The kernel actually doesn't bother with this, i.e. an open on an flink
name will always create a new handle. Given that it was a major pita to
get the prime reimporting going (due to a pile of funny lifetime issues
around reference loops and some assorted locking fun) I'm not volunteering
to fix this ;-) And I also think that a piece of userspace which both
flink-opens and prime imports on the same buffer gets both pieces.

Otoh this can't hurt either, so if you want to stick with this hunk maybe
add a small comment saying that the kernel lies. Or just remove it. Either
way:

Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>

Aside: I think drm is the only subsystem that goes out of it's way to
ensure a unique relationship between dmabuf and other handles and
underlying objects. If you throw v4l into the mix (e.g. by building a
gstreamer pipe that feeds into an egl image or so) I expect some fun to
happen. Otoh no open-source v4l driver for intel socs, so lalala ;-)

> +
> +	bo_gem = calloc(1, sizeof(*bo_gem));
> +	if (!bo_gem)
> +		return NULL;
> +
>  	bo_gem->bo.size = open_arg.size;
>  	bo_gem->bo.offset = 0;
>  	bo_gem->bo.virtual = NULL;
> @@ -2451,8 +2466,25 @@ drm_intel_bo_gem_create_from_prime(drm_intel_bufmgr *bufmgr, int prime_fd, int s
>  	uint32_t handle;
>  	drm_intel_bo_gem *bo_gem;
>  	struct drm_i915_gem_get_tiling get_tiling;
> +	drmMMListHead *list;
>  
>  	ret = drmPrimeFDToHandle(bufmgr_gem->fd, prime_fd, &handle);
> +
> +	/*
> +	 * See if the kernel has already returned this buffer to us. Just as
> +	 * for named buffers, we must not create two bo's pointing at the same
> +	 * kernel object
> +	 */
> +	for (list = bufmgr_gem->named.next;
> +	     list != &bufmgr_gem->named;
> +	     list = list->next) {
> +		bo_gem = DRMLISTENTRY(drm_intel_bo_gem, list, name_list);
> +		if (bo_gem->gem_handle == handle) {
> +			drm_intel_gem_bo_reference(&bo_gem->bo);
> +			return &bo_gem->bo;
> +		}
> +	}
> +
>  	if (ret) {
>  	  fprintf(stderr,"ret is %d %d\n", ret, errno);
>  		return NULL;
> @@ -2487,8 +2519,8 @@ drm_intel_bo_gem_create_from_prime(drm_intel_bufmgr *bufmgr, int prime_fd, int s
>  	bo_gem->has_error = false;
>  	bo_gem->reusable = false;
>  
> -	DRMINITLISTHEAD(&bo_gem->name_list);
>  	DRMINITLISTHEAD(&bo_gem->vma_list);
> +	DRMLISTADDTAIL(&bo_gem->name_list, &bufmgr_gem->named);
>  
>  	VG_CLEAR(get_tiling);
>  	get_tiling.handle = bo_gem->gem_handle;
> @@ -2513,6 +2545,9 @@ drm_intel_bo_gem_export_to_prime(drm_intel_bo *bo, int *prime_fd)
>  	drm_intel_bufmgr_gem *bufmgr_gem = (drm_intel_bufmgr_gem *) bo->bufmgr;
>  	drm_intel_bo_gem *bo_gem = (drm_intel_bo_gem *) bo;
>  
> +        if (DRMLISTEMPTY(&bo_gem->name_list))
> +                DRMLISTADDTAIL(&bo_gem->name_list, &bufmgr_gem->named);
> +
>  	if (drmPrimeHandleToFD(bufmgr_gem->fd, bo_gem->gem_handle,
>  			       DRM_CLOEXEC, prime_fd) != 0)
>  		return -errno;
> @@ -2542,7 +2577,8 @@ drm_intel_gem_bo_flink(drm_intel_bo *bo, uint32_t * name)
>  		bo_gem->global_name = flink.name;
>  		bo_gem->reusable = false;
>  
> -		DRMLISTADDTAIL(&bo_gem->name_list, &bufmgr_gem->named);
> +                if (DRMLISTEMPTY(&bo_gem->name_list))
> +                        DRMLISTADDTAIL(&bo_gem->name_list, &bufmgr_gem->named);
>  	}
>  
>  	*name = bo_gem->global_name;
> -- 
> 1.8.4.4
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch