Re: [PATCH 1/2] drm/prime: keep a reference from the handle to exported dma-buf (v5)

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On Fri, 2013-04-19 at 11:11 +1000, Dave Airlie wrote:
> Currently we have a problem with this:
> 1. i915: create gem object
> 2. i915: export gem object to prime
> 3. radeon: import gem object
> 4. close prime fd
> 5. radeon: unref object
> 6. i915: unref object
> 
> i915 has an imported object reference in its file priv, that isn't
> cleaned up properly until fd close. The reference gets added at step 2,
> but at step 6 we don't have enough info to clean it up.
> 
> The solution is to take a reference on the dma-buf when we export it,
> and drop the reference when the gem handle goes away.
> 
> So when we export a dma_buf from a gem object, we keep track of it
> with the handle, we take a reference to the dma_buf. When we close
> the handle (i.e. userspace is finished with the buffer), we drop
> the reference to the dma_buf, and it gets collected.
> 
> This patch isn't meant to fix any other problem or bikesheds, and it doesn't
> fix any races with other scenarios.
> 
> v1.1: move export symbol line back up.
> 
> v2: okay I had to do a bit more, as the first patch showed a leak
> on one of my tests, that I found using the dma-buf debugfs support,
> the problem case is exporting a buffer twice with the same handle,
> we'd add another export handle for it unnecessarily, however
> we now fail if we try to export the same object with a different gem handle,
> however I'm not sure if that is a case I want to support, and I've
> gotten the code to WARN_ON if we hit something like that.
> 
> v2.1: rebase this patch, write better commit msg.
> v3: cleanup error handling, track import vs export in linked list,
> these two patches were separate previously, but seem to work better
> like this.
> v4: danvet is correct, this code is no longer useful, since the buffer
> better exist, so remove it.
> v5: always take a reference to the dma buf object, import or export.
> (Imre Deak contributed this originally)
> 
> Signed-off-by: Dave Airlie <airlied@xxxxxxxxxx>

drm_prime_destroy_file_private() lacks a drm_buf_put(). A separate
issue, but the list should actually be empty at that point so perhaps we
should warn if it's not.

bikeshed: we don't really need the PRIME_{EXPORT,IMPORT} tracking.

Otherwise looks ok:
Reviewed-by: Imre Deak <imre.deak@xxxxxxxxx>

> ---
>  drivers/gpu/drm/drm_gem.c   |  4 +-
>  drivers/gpu/drm/drm_prime.c | 93 ++++++++++++++++++++++++++++-----------------
>  include/drm/drmP.h          |  4 +-
>  3 files changed, 63 insertions(+), 38 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
> index af779ae..cf919e3 100644
> --- a/drivers/gpu/drm/drm_gem.c
> +++ b/drivers/gpu/drm/drm_gem.c
> @@ -205,11 +205,11 @@ static void
>  drm_gem_remove_prime_handles(struct drm_gem_object *obj, struct drm_file *filp)
>  {
>  	if (obj->import_attach) {
> -		drm_prime_remove_imported_buf_handle(&filp->prime,
> +		drm_prime_remove_buf_handle(&filp->prime,
>  				obj->import_attach->dmabuf);
>  	}
>  	if (obj->export_dma_buf) {
> -		drm_prime_remove_imported_buf_handle(&filp->prime,
> +		drm_prime_remove_buf_handle(&filp->prime,
>  				obj->export_dma_buf);
>  	}
>  }
> diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
> index 366910d..eb7c38d 100644
> --- a/drivers/gpu/drm/drm_prime.c
> +++ b/drivers/gpu/drm/drm_prime.c
> @@ -57,10 +57,14 @@
>   * use the drm_gem_prime_{import,export} helpers.
>   */
>  
> +#define PRIME_IMPORT 1
> +#define PRIME_EXPORT 2
> +
>  struct drm_prime_member {
>  	struct list_head entry;
>  	struct dma_buf *dma_buf;
>  	uint32_t handle;
> +	int type;
>  };
>  
>  static struct sg_table *drm_gem_map_dma_buf(struct dma_buf_attachment *attach,
> @@ -157,6 +161,8 @@ static const struct dma_buf_ops drm_gem_prime_dmabuf_ops =  {
>  	.vunmap = drm_gem_dmabuf_vunmap,
>  };
>  
> +static int drm_prime_add_exported_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf, uint32_t handle);
> +
>  /**
>   * DOC: PRIME Helpers
>   *
> @@ -200,7 +206,8 @@ int drm_gem_prime_handle_to_fd(struct drm_device *dev,
>  {
>  	struct drm_gem_object *obj;
>  	void *buf;
> -	int ret;
> +	int ret = 0;
> +	struct dma_buf *dmabuf;
>  
>  	obj = drm_gem_object_lookup(dev, file_priv, handle);
>  	if (!obj)
> @@ -209,43 +216,44 @@ int drm_gem_prime_handle_to_fd(struct drm_device *dev,
>  	mutex_lock(&file_priv->prime.lock);
>  	/* re-export the original imported object */
>  	if (obj->import_attach) {
> -		get_dma_buf(obj->import_attach->dmabuf);
> -		*prime_fd = dma_buf_fd(obj->import_attach->dmabuf, flags);
> -		drm_gem_object_unreference_unlocked(obj);
> -		mutex_unlock(&file_priv->prime.lock);
> -		return 0;
> +		dmabuf = obj->import_attach->dmabuf;
> +		goto out_have_obj;
>  	}
>  
>  	if (obj->export_dma_buf) {
> -		get_dma_buf(obj->export_dma_buf);
> -		*prime_fd = dma_buf_fd(obj->export_dma_buf, flags);
> -		drm_gem_object_unreference_unlocked(obj);
> -	} else {
> -		buf = dev->driver->gem_prime_export(dev, obj, flags);
> -		if (IS_ERR(buf)) {
> -			/* normally the created dma-buf takes ownership of the ref,
> -			 * but if that fails then drop the ref
> -			 */
> -			drm_gem_object_unreference_unlocked(obj);
> -			mutex_unlock(&file_priv->prime.lock);
> -			return PTR_ERR(buf);
> -		}
> -		obj->export_dma_buf = buf;
> -		*prime_fd = dma_buf_fd(buf, flags);
> +		dmabuf = obj->export_dma_buf;
> +		goto out_have_obj;
>  	}
> +
> +	buf = dev->driver->gem_prime_export(dev, obj, flags);
> +	if (IS_ERR(buf)) {
> +		/* normally the created dma-buf takes ownership of the ref,
> +		 * but if that fails then drop the ref
> +		 */
> +		ret = PTR_ERR(buf);
> +		goto out;
> +	}
> +	obj->export_dma_buf = buf;
> +
>  	/* if we've exported this buffer the cheat and add it to the import list
>  	 * so we get the correct handle back
>  	 */
> -	ret = drm_prime_add_imported_buf_handle(&file_priv->prime,
> -			obj->export_dma_buf, handle);
> -	if (ret) {
> -		drm_gem_object_unreference_unlocked(obj);
> -		mutex_unlock(&file_priv->prime.lock);
> -		return ret;
> -	}
> +	ret = drm_prime_add_exported_buf_handle(&file_priv->prime,
> +						obj->export_dma_buf, handle);
> +	if (ret)
> +		goto out;
>  
> +	*prime_fd = dma_buf_fd(buf, flags);
>  	mutex_unlock(&file_priv->prime.lock);
>  	return 0;
> +
> +out_have_obj:
> +	get_dma_buf(dmabuf);
> +	*prime_fd = dma_buf_fd(dmabuf, flags);
> +out:
> +	drm_gem_object_unreference_unlocked(obj);
> +	mutex_unlock(&file_priv->prime.lock);
> +	return ret;
>  }
>  EXPORT_SYMBOL(drm_gem_prime_handle_to_fd);
>  
> @@ -314,7 +322,7 @@ int drm_gem_prime_fd_to_handle(struct drm_device *dev,
>  
>  	mutex_lock(&file_priv->prime.lock);
>  
> -	ret = drm_prime_lookup_imported_buf_handle(&file_priv->prime,
> +	ret = drm_prime_lookup_buf_handle(&file_priv->prime,
>  			dma_buf, handle);
>  	if (!ret) {
>  		ret = 0;
> @@ -491,7 +499,7 @@ void drm_prime_destroy_file_private(struct drm_prime_file_private *prime_fpriv)
>  }
>  EXPORT_SYMBOL(drm_prime_destroy_file_private);
>  
> -int drm_prime_add_imported_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf, uint32_t handle)
> +static int drm_prime_add_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf, uint32_t handle, int type)
>  {
>  	struct drm_prime_member *member;
>  
> @@ -499,14 +507,27 @@ int drm_prime_add_imported_buf_handle(struct drm_prime_file_private *prime_fpriv
>  	if (!member)
>  		return -ENOMEM;
>  
> +	get_dma_buf(dma_buf);
>  	member->dma_buf = dma_buf;
>  	member->handle = handle;
> +	member->type = type;
>  	list_add(&member->entry, &prime_fpriv->head);
>  	return 0;
>  }
> +
> +int drm_prime_add_imported_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf, uint32_t handle)
> +{
> +	return drm_prime_add_buf_handle(prime_fpriv, dma_buf, handle, PRIME_IMPORT);
> +}
>  EXPORT_SYMBOL(drm_prime_add_imported_buf_handle);
>  
> -int drm_prime_lookup_imported_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf, uint32_t *handle)
> +static int drm_prime_add_exported_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf, uint32_t handle)
> +{
> +	/* take a reference to the buf handle for this case */
> +	return drm_prime_add_buf_handle(prime_fpriv, dma_buf, handle, PRIME_EXPORT);
> +}
> +
> +int drm_prime_lookup_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf, uint32_t *handle)
>  {
>  	struct drm_prime_member *member;
>  
> @@ -518,19 +539,23 @@ int drm_prime_lookup_imported_buf_handle(struct drm_prime_file_private *prime_fp
>  	}
>  	return -ENOENT;
>  }
> -EXPORT_SYMBOL(drm_prime_lookup_imported_buf_handle);
> +EXPORT_SYMBOL(drm_prime_lookup_buf_handle);
>  
> -void drm_prime_remove_imported_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf)
> +void drm_prime_remove_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf)
>  {
>  	struct drm_prime_member *member, *safe;
>  
>  	mutex_lock(&prime_fpriv->lock);
>  	list_for_each_entry_safe(member, safe, &prime_fpriv->head, entry) {
>  		if (member->dma_buf == dma_buf) {
> +			dma_buf_put(dma_buf);
>  			list_del(&member->entry);
>  			kfree(member);
>  		}
>  	}
>  	mutex_unlock(&prime_fpriv->lock);
>  }
> -EXPORT_SYMBOL(drm_prime_remove_imported_buf_handle);
> +EXPORT_SYMBOL(drm_prime_remove_buf_handle);
> +
> +
> +
> diff --git a/include/drm/drmP.h b/include/drm/drmP.h
> index 2d94d74..69712a6 100644
> --- a/include/drm/drmP.h
> +++ b/include/drm/drmP.h
> @@ -1594,8 +1594,8 @@ extern void drm_prime_gem_destroy(struct drm_gem_object *obj, struct sg_table *s
>  void drm_prime_init_file_private(struct drm_prime_file_private *prime_fpriv);
>  void drm_prime_destroy_file_private(struct drm_prime_file_private *prime_fpriv);
>  int drm_prime_add_imported_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf, uint32_t handle);
> -int drm_prime_lookup_imported_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf, uint32_t *handle);
> -void drm_prime_remove_imported_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf);
> +int drm_prime_lookup_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf, uint32_t *handle);
> +void drm_prime_remove_buf_handle(struct drm_prime_file_private *prime_fpriv, struct dma_buf *dma_buf);
>  
>  int drm_prime_add_dma_buf(struct drm_device *dev, struct drm_gem_object *obj);
>  int drm_prime_lookup_obj(struct drm_device *dev, struct dma_buf *buf,


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