drm/prime: Take a ref on the drm_dev when exporting a dma_buf

dma_buf may live a long time, longer than the last direct user of the
driver. We already hold a reference to the owner module (that prevents
the object code from disappearing), but there is no reference to the
drm_dev - so the pointers to the driver backend themselves may vanish.

v2: Resist temptation to fix the bug in armada_gem.c not setting the
correct flags on the exported dma-buf (it should pass the flags through
and not be arbitrarily setting O_RDWR).

Use a common wrapper for exporting the dmabuf and acquiring the
reference to the drm_device.

Testcase: igt/vgem_basic/unload
Suggested-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Petri Latvala <petri.latvala@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: stable@vger.kernel.org
Tested-by: Petri Latvala <petri.latvala@intel.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20161005122145.1507-2-chris@chris-wilson.co.uk

drivers/gpu/drm/armada/armada_gem.c

@@ -547,7 +547,7 @@ armada_gem_prime_export(struct drm_device *dev, struct drm_gem_object *obj,
 	exp_info.flags = O_RDWR;
 	exp_info.priv = obj;
 
-	return dma_buf_export(&exp_info);
+	return drm_gem_dmabuf_export(dev, &exp_info);
 }
 
 struct drm_gem_object *

drivers/gpu/drm/drm_prime.c

@@ -283,19 +283,47 @@ static void drm_gem_unmap_dma_buf(struct dma_buf_attachment *attach,
 	/* nothing to be done here */
 }
 
+/**
+ * drm_gem_dmabuf_export - dma_buf export implementation for GEM
+ * @dma_buf: buffer to be exported
+ *
+ * This wraps dma_buf_export() for use by generic GEM drivers that are using
+ * drm_gem_dmabuf_release(). In addition to calling dma_buf_export(), we take
+ * a reference to the drm_device which is released by drm_gem_dmabuf_release().
+ *
+ * Returns the new dmabuf.
+ */
+struct dma_buf *drm_gem_dmabuf_export(struct drm_device *dev,
+				      struct dma_buf_export_info *exp_info)
+{
+	struct dma_buf *dma_buf;
+
+	dma_buf = dma_buf_export(exp_info);
+	if (!IS_ERR(dma_buf))
+		drm_dev_ref(dev);
+
+	return dma_buf;
+}
+EXPORT_SYMBOL(drm_gem_dmabuf_export);
+
 /**
  * drm_gem_dmabuf_release - dma_buf release implementation for GEM
  * @dma_buf: buffer to be released
  *
  * Generic release function for dma_bufs exported as PRIME buffers. GEM drivers
  * must use this in their dma_buf ops structure as the release callback.
+ * drm_gem_dmabuf_release() should be used in conjunction with
+ * drm_gem_dmabuf_export().
  */
 void drm_gem_dmabuf_release(struct dma_buf *dma_buf)
 {
 	struct drm_gem_object *obj = dma_buf->priv;
+	struct drm_device *dev = obj->dev;
 
 	/* drop the reference on the export fd holds */
 	drm_gem_object_unreference_unlocked(obj);
+
+	drm_dev_unref(dev);
 }
 EXPORT_SYMBOL(drm_gem_dmabuf_release);
 
@@ -412,7 +440,7 @@ struct dma_buf *drm_gem_prime_export(struct drm_device *dev,
 	if (dev->driver->gem_prime_res_obj)
 		exp_info.resv = dev->driver->gem_prime_res_obj(obj);
 
-	return dma_buf_export(&exp_info);
+	return drm_gem_dmabuf_export(dev, &exp_info);
 }
 EXPORT_SYMBOL(drm_gem_prime_export);
 

drivers/gpu/drm/i915/i915_gem_dmabuf.c

@@ -283,7 +283,7 @@ struct dma_buf *i915_gem_prime_export(struct drm_device *dev,
 			return ERR_PTR(ret);
 	}
 
-	dma_buf = dma_buf_export(&exp_info);
+	dma_buf = drm_gem_dmabuf_export(dev, &exp_info);
 	if (IS_ERR(dma_buf))
 		return dma_buf;
 

drivers/gpu/drm/tegra/gem.c

@@ -613,7 +613,7 @@ struct dma_buf *tegra_gem_prime_export(struct drm_device *drm,
 	exp_info.flags = flags;
 	exp_info.priv = gem;
 
-	return dma_buf_export(&exp_info);
+	return drm_gem_dmabuf_export(drm, &exp_info);
 }
 
 struct drm_gem_object *tegra_gem_prime_import(struct drm_device *drm,

drivers/gpu/drm/udl/udl_dmabuf.c

@@ -209,7 +209,7 @@ struct dma_buf *udl_gem_prime_export(struct drm_device *dev,
 	exp_info.flags = flags;
 	exp_info.priv = obj;
 
-	return dma_buf_export(&exp_info);
+	return drm_gem_dmabuf_export(dev, &exp_info);
 }
 
 static int udl_prime_create(struct drm_device *dev,

include/drm/drmP.h

@@ -1011,6 +1011,8 @@ static inline int drm_debugfs_remove_files(const struct drm_info_list *files,
 }
 #endif
 
+struct dma_buf_export_info;
+
 extern struct dma_buf *drm_gem_prime_export(struct drm_device *dev,
 					    struct drm_gem_object *obj,
 					    int flags);
@@ -1021,6 +1023,8 @@ extern struct drm_gem_object *drm_gem_prime_import(struct drm_device *dev,
 		struct dma_buf *dma_buf);
 extern int drm_gem_prime_fd_to_handle(struct drm_device *dev,
 		struct drm_file *file_priv, int prime_fd, uint32_t *handle);
+struct dma_buf *drm_gem_dmabuf_export(struct drm_device *dev,
+				      struct dma_buf_export_info *exp_info);
 extern void drm_gem_dmabuf_release(struct dma_buf *dma_buf);
 
 extern int drm_prime_sg_to_page_addr_arrays(struct sg_table *sgt, struct page **pages,