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.vet...@ffwll.ch>
Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
Cc: Petri Latvala <petri.latv...@intel.com>
Cc: Daniel Vetter <daniel.vet...@ffwll.ch>
Cc: sta...@vger.kernel.org
Tested-by: Petri Latvala <petri.latv...@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

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