[PATCH] drm/prime: keep a reference from the handle to exported dma-buf (v4)

[PATCH] drm/prime: keep a reference from the handle to exported dma-buf (v4)

[Dave Airlie]

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.

Signed-off-by: Dave Airlie <airlied@redhat.com>
---
 drivers/gpu/drm/drm_gem.c   |  4 +-
 drivers/gpu/drm/drm_prime.c | 95 +++++++++++++++++++++++++++++----------------
 include/drm/drmP.h          |  4 +-
 3 files changed, 65 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..b4ed808 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 +206,9 @@ 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;
+	uint32_t exp_handle;
 
 	obj = drm_gem_object_lookup(dev, file_priv, handle);
 	if (!obj)
@@ -209,43 +217,44 @@ 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 +323,7 @@ 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 +500,7 @@ 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;
 
@@ -501,12 +510,25 @@ int drm_prime_add_imported_buf_handle(struct drm_prime_file_private *prime_fpriv
 
 	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 */
+	get_dma_buf(dma_buf);
+	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 +540,24 @@ 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) {
+			if (member->type == PRIME_EXPORT)
+				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,
-- 
1.8.2

Re: [PATCH] drm/prime: keep a reference from the handle to exported dma-buf (v4)

[Daniel Vetter]

On Wed, Apr 17, 2013 at 02:38:02PM +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.
> 
> Signed-off-by: Dave Airlie <airlied@redhat.com>

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

On bikeshed review level I wonder whether we shouldn't just grab a
reference unconditonally when inserting it into the handle_to_fd lookup
lists. But I need to think through a few other cases and apparently the
self-import test is still a bit broken. So this is material for follow-up
patches.
-Daniel

> ---
>  drivers/gpu/drm/drm_gem.c   |  4 +-
>  drivers/gpu/drm/drm_prime.c | 95 +++++++++++++++++++++++++++++----------------
>  include/drm/drmP.h          |  4 +-
>  3 files changed, 65 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..b4ed808 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 +206,9 @@ 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;
> +	uint32_t exp_handle;
>  
>  	obj = drm_gem_object_lookup(dev, file_priv, handle);
>  	if (!obj)
> @@ -209,43 +217,44 @@ 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 +323,7 @@ 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 +500,7 @@ 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;
>  
> @@ -501,12 +510,25 @@ int drm_prime_add_imported_buf_handle(struct drm_prime_file_private *prime_fpriv
>  
>  	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 */
> +	get_dma_buf(dma_buf);
> +	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 +540,24 @@ 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) {
> +			if (member->type == PRIME_EXPORT)
> +				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,
> -- 
> 1.8.2
> 
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/dri-devel

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

Re: [PATCH] drm/prime: keep a reference from the handle to exported dma-buf (v4)

[Imre Deak]

On Wed, 2013-04-17 at 10:21 +0200, Daniel Vetter wrote:
> On Wed, Apr 17, 2013 at 02:38:02PM +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.
> > 
> > Signed-off-by: Dave Airlie <airlied@redhat.com>
> 
> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> 
> On bikeshed review level I wonder whether we shouldn't just grab a
> reference unconditonally when inserting it into the handle_to_fd lookup
> lists. But I need to think through a few other cases and apparently the
> self-import test is still a bit broken. So this is material for follow-up
> patches.

Yes, this is needed, otherwise closing the prime fd will leave stale
pointers to the dma buf in the importer's lookup table. I've sent an
update to igt/prime_self_test to intel-gfx for showing this.

--Imre

> -Daniel
> 
> > ---
> >  drivers/gpu/drm/drm_gem.c   |  4 +-
> >  drivers/gpu/drm/drm_prime.c | 95 +++++++++++++++++++++++++++++----------------
> >  include/drm/drmP.h          |  4 +-
> >  3 files changed, 65 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..b4ed808 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 +206,9 @@ 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;
> > +	uint32_t exp_handle;
> >  
> >  	obj = drm_gem_object_lookup(dev, file_priv, handle);
> >  	if (!obj)
> > @@ -209,43 +217,44 @@ 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 +323,7 @@ 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 +500,7 @@ 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;
> >  
> > @@ -501,12 +510,25 @@ int drm_prime_add_imported_buf_handle(struct drm_prime_file_private *prime_fpriv
> >  
> >  	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 */
> > +	get_dma_buf(dma_buf);
> > +	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 +540,24 @@ 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) {
> > +			if (member->type == PRIME_EXPORT)
> > +				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,
> > -- 
> > 1.8.2
> > 
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel@lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/dri-devel
> 

Re: [PATCH] drm/prime: keep a reference from the handle to exported dma-buf (v4)

[Dave Airlie]

On Thu, Apr 18, 2013 at 2:16 AM, Imre Deak <imre.deak@intel.com> wrote:
> On Wed, 2013-04-17 at 10:21 +0200, Daniel Vetter wrote:
>> On Wed, Apr 17, 2013 at 02:38:02PM +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.
>> >
>> > Signed-off-by: Dave Airlie <airlied@redhat.com>
>>
>> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
>>
>> On bikeshed review level I wonder whether we shouldn't just grab a
>> reference unconditonally when inserting it into the handle_to_fd lookup
>> lists. But I need to think through a few other cases and apparently the
>> self-import test is still a bit broken. So this is material for follow-up
>> patches.
>
> Yes, this is needed, otherwise closing the prime fd will leave stale
> pointers to the dma buf in the importer's lookup table. I've sent an
> update to igt/prime_self_test to intel-gfx for showing this.
>

Okay I've spent time on this today and yes I agree, so I'll post v5 of my patch
with that in it.

I'd like to also merge your other patch, it seems fine.

Dave.