drm/i915: Markup GEM API with lockdep asserts

Add lockdep_assert_held(struct_mutex) to the API preamble of the
internal GEM interfaces.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20161028125858.23563-9-chris@chris-wilson.co.uk
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 96995d6..a1b9801 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -3432,6 +3432,7 @@ int __must_check i915_vma_put_fence(struct i915_vma *vma);
 static inline bool
 i915_vma_pin_fence(struct i915_vma *vma)
 {
+	lockdep_assert_held(&vma->vm->dev->struct_mutex);
 	if (vma->fence) {
 		vma->fence->pin_count++;
 		return true;
@@ -3450,6 +3451,7 @@ i915_vma_pin_fence(struct i915_vma *vma)
 static inline void
 i915_vma_unpin_fence(struct i915_vma *vma)
 {
+	lockdep_assert_held(&vma->vm->dev->struct_mutex);
 	if (vma->fence) {
 		GEM_BUG_ON(vma->fence->pin_count <= 0);
 		vma->fence->pin_count--;