drm/i915: fix invalid reference handling of the default ctx obj

Otherwise we end up trying to unpin a freed object and BUG.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 4 insertions, 14 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index 65639ad72808..873119f2436e 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -419,8 +419,11 @@ static int do_switch(struct drm_i915_gem_object *from_obj,
                 from_obj->dirty = 1;
                 BUG_ON(from_obj->ring != to->ring);
                 i915_gem_object_unpin(from_obj);
+
+                drm_gem_object_unreference(&from_obj->base);
         }
 
+        drm_gem_object_reference(&to->obj->base);
         ring->last_context_obj = to->obj;
         to->is_initialized = true;
 
@@ -470,20 +473,7 @@ int i915_switch_context(struct intel_ring_buffer *ring,
         if (from_obj == to->obj)
                 return 0;
 
-        ret = do_switch(from_obj, to, i915_gem_next_request_seqno(to->ring));
-        if (ret)
-                return ret;
-
-        /* Just to make the code a little cleaner we take the object reference
-         * after the switch was successful. It would be more intuitive to ref
-         * the 'to' object before the switch but we know the refcount must be >0
-         * if context_get() succeeded, and we hold struct mutex. So it's safe to
-         * do this here/now
-         */
-        drm_gem_object_reference(&to->obj->base);
-        if (from_obj != NULL)
-                drm_gem_object_unreference(&from_obj->base);
-        return ret;
+        return do_switch(from_obj, to, i915_gem_next_request_seqno(to->ring));
 }
 
 int i915_gem_context_create_ioctl(struct drm_device *dev, void *data,