[PATCH v3 2/3] drm/prime: Take a ref on the drm_dev when exporting a dma_buf

[Chris Wilson <chris@chris-wilson.co.uk>]

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.

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>
---
 drivers/gpu/drm/armada/armada_gem.c    |  9 +++++++--
 drivers/gpu/drm/drm_prime.c            | 10 +++++++++-
 drivers/gpu/drm/i915/i915_gem_dmabuf.c |  1 +
 drivers/gpu/drm/tegra/gem.c            |  7 ++++++-
 drivers/gpu/drm/udl/udl_dmabuf.c       |  7 ++++++-
 5 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/armada/armada_gem.c b/drivers/gpu/drm/armada/armada_gem.c
index cb8f0347b934..bdd3af043827 100644
--- a/drivers/gpu/drm/armada/armada_gem.c
+++ b/drivers/gpu/drm/armada/armada_gem.c
@@ -541,13 +541,18 @@ armada_gem_prime_export(struct drm_device *dev, struct drm_gem_object *obj,
 	int flags)
 {
 	DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
+	struct dma_buf *dma_buf;
 
 	exp_info.ops = &armada_gem_prime_dmabuf_ops;
 	exp_info.size = obj->size;
-	exp_info.flags = O_RDWR;
+	exp_info.flags = flags;
 	exp_info.priv = obj;
 
-	return dma_buf_export(&exp_info);
+	dma_buf = dma_buf_export(&exp_info);
+	if (!IS_ERR(dma_buf))
+		drm_dev_ref(dev);
+
+	return dma_buf;
 }
 
 struct drm_gem_object *
diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index 80907b34d857..5081f187d9e3 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -293,9 +293,12 @@ static void drm_gem_unmap_dma_buf(struct dma_buf_attachment *attach,
 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);
 
@@ -408,11 +411,16 @@ struct dma_buf *drm_gem_prime_export(struct drm_device *dev,
 		.flags = flags,
 		.priv = obj,
 	};
+	struct dma_buf *dma_buf;
 
 	if (dev->driver->gem_prime_res_obj)
 		exp_info.resv = dev->driver->gem_prime_res_obj(obj);
 
-	return dma_buf_export(&exp_info);
+	dma_buf = dma_buf_export(&exp_info);
+	if (!IS_ERR(dma_buf))
+		drm_dev_ref(dev);
+
+	return dma_buf;
 }
 EXPORT_SYMBOL(drm_gem_prime_export);
 
diff --git a/drivers/gpu/drm/i915/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/i915_gem_dmabuf.c
index 10265bb35604..b58b2e63add1 100644
--- a/drivers/gpu/drm/i915/i915_gem_dmabuf.c
+++ b/drivers/gpu/drm/i915/i915_gem_dmabuf.c
@@ -288,6 +288,7 @@ struct dma_buf *i915_gem_prime_export(struct drm_device *dev,
 		return dma_buf;
 
 	export_fences(obj, dma_buf);
+	drm_dev_ref(obj->base.dev);
 	return dma_buf;
 }
 
diff --git a/drivers/gpu/drm/tegra/gem.c b/drivers/gpu/drm/tegra/gem.c
index aa60d9909ea2..aaae8b6ba668 100644
--- a/drivers/gpu/drm/tegra/gem.c
+++ b/drivers/gpu/drm/tegra/gem.c
@@ -607,13 +607,18 @@ struct dma_buf *tegra_gem_prime_export(struct drm_device *drm,
 				       int flags)
 {
 	DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
+	struct dma_buf *dma_buf;
 
 	exp_info.ops = &tegra_gem_prime_dmabuf_ops;
 	exp_info.size = gem->size;
 	exp_info.flags = flags;
 	exp_info.priv = gem;
 
-	return dma_buf_export(&exp_info);
+	dma_buf = dma_buf_export(&exp_info);
+	if (!IS_ERR(dma_buf))
+		drm_dev_ref(drm);
+
+	return dma_buf;
 }
 
 struct drm_gem_object *tegra_gem_prime_import(struct drm_device *drm,
diff --git a/drivers/gpu/drm/udl/udl_dmabuf.c b/drivers/gpu/drm/udl/udl_dmabuf.c
index e2243edd1ce3..249cc1072112 100644
--- a/drivers/gpu/drm/udl/udl_dmabuf.c
+++ b/drivers/gpu/drm/udl/udl_dmabuf.c
@@ -203,13 +203,18 @@ struct dma_buf *udl_gem_prime_export(struct drm_device *dev,
 				     struct drm_gem_object *obj, int flags)
 {
 	DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
+	struct dma_buf *dma_buf;
 
 	exp_info.ops = &udl_dmabuf_ops;
 	exp_info.size = obj->size;
 	exp_info.flags = flags;
 	exp_info.priv = obj;
 
-	return dma_buf_export(&exp_info);
+	dma_buf = dma_buf_export(&exp_info);
+	if (!IS_ERR(dma_buf))
+		drm_dev_ref(dev);
+
+	return dma_buf;
 }
 
 static int udl_prime_create(struct drm_device *dev,
-- 
2.9.3