After unbinding drm, the userspace may still has a chance to access
gem buf.

Add a sanity check for a NULL dev_private to prevent that from
happening.

Signed-off-by: Jeffy Chen <jeffy.c...@rock-chips.com>
---

Changes in v3:
Address Daniel Vetter <dan...@ffwll.ch>'s comments.
Update commit message.

Changes in v2: None

 drivers/gpu/drm/rockchip/rockchip_drm_gem.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c 
b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
index df9e570..205a3dc 100644
--- a/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
+++ b/drivers/gpu/drm/rockchip/rockchip_drm_gem.c
@@ -184,6 +184,9 @@ static int rockchip_gem_alloc_buf(struct 
rockchip_gem_object *rk_obj,
        struct drm_device *drm = obj->dev;
        struct rockchip_drm_private *private = drm->dev_private;
 
+       if (!private)
+               return -ENODEV;
+
        if (private->domain)
                return rockchip_gem_alloc_iommu(rk_obj, alloc_kmap);
        else
@@ -208,6 +211,11 @@ static void rockchip_gem_free_dma(struct 
rockchip_gem_object *rk_obj)
 
 static void rockchip_gem_free_buf(struct rockchip_gem_object *rk_obj)
 {
+       struct drm_device *drm = rk_obj->base.dev;
+
+       if (!drm->dev_private)
+               return;
+
        if (rk_obj->pages)
                rockchip_gem_free_iommu(rk_obj);
        else
-- 
2.1.4


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