drm/i915: GEM operations need to be done under the big lock

VMA creation and GEM list management need the big lock.

v2:

Mutex unlock ended on the wrong path somehow. (0-day, Julia Lawall)

Not to mention drm_gem_object_unreference was there in existing
code with no mutex held.

v3:

Some callers of i915_gem_object_create_stolen_for_preallocated
already hold the lock so move the mutex into the other caller
as well.

v4:

Changed to lockdep_assert_held. (Chris Wilson)
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/i915_gem_stolen.c

@@ -638,6 +638,8 @@ i915_gem_object_create_stolen_for_preallocated(struct drm_device *dev,
 	if (!drm_mm_initialized(&dev_priv->mm.stolen))
 		return NULL;
 
+	lockdep_assert_held(&dev->struct_mutex);
+
 	DRM_DEBUG_KMS("creating preallocated stolen object: stolen_offset=%x, gtt_offset=%x, size=%x\n",
 			stolen_offset, gtt_offset, size);
 

drivers/gpu/drm/i915/intel_display.c

@@ -2551,12 +2551,16 @@ intel_alloc_initial_plane_obj(struct intel_crtc *crtc,
 	if (size_aligned * 2 > dev_priv->gtt.stolen_usable_size)
 		return false;
 
+	mutex_lock(&dev->struct_mutex);
+
 	obj = i915_gem_object_create_stolen_for_preallocated(dev,
 							     base_aligned,
 							     base_aligned,
 							     size_aligned);
-	if (!obj)
+	if (!obj) {
+		mutex_unlock(&dev->struct_mutex);
 		return false;
+	}
 
 	obj->tiling_mode = plane_config->tiling;
 	if (obj->tiling_mode == I915_TILING_X)
@@ -2569,12 +2573,12 @@ intel_alloc_initial_plane_obj(struct intel_crtc *crtc,
 	mode_cmd.modifier[0] = fb->modifier[0];
 	mode_cmd.flags = DRM_MODE_FB_MODIFIERS;
 
-	mutex_lock(&dev->struct_mutex);
 	if (intel_framebuffer_init(dev, to_intel_framebuffer(fb),
 				   &mode_cmd, obj)) {
 		DRM_DEBUG_KMS("intel fb init failed\n");
 		goto out_unref_obj;
 	}
+
 	mutex_unlock(&dev->struct_mutex);
 
 	DRM_DEBUG_KMS("initial plane fb obj %p\n", obj);