drm/i915: Improve lockdep tracking for obj->mm.lock

The shrinker may appear to recurse into obj->mm.lock as the shrinker may
be called from a direct reclaim path whilst handling get_pages. We
filter out recursing on the same obj->mm.lock by inspecting
obj->mm.pages, but we do want to take the lock on a second object in
order to reap their pages. lockdep spots the recursion on the same
lockclass and needs annotation to avoid a false positive. To keep the
two paths distinct, create an enum to indicate which subclass of
obj->mm.lock we are using. This removes the false positive and avoids
masking real bugs.

Suggested-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20161101121134.27504-1-chris@chris-wilson.co.uk
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

1 files changed, 7 insertions, 1 deletions

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 9143129cd851..086396e16de7 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -3287,7 +3287,13 @@ i915_gem_object_unpin_pages(struct drm_i915_gem_object *obj)
 	__i915_gem_object_unpin_pages(obj);
 }
 
-void __i915_gem_object_put_pages(struct drm_i915_gem_object *obj);
+enum i915_mm_subclass { /* lockdep subclass for obj->mm.lock */
+	I915_MM_NORMAL = 0,
+	I915_MM_SHRINKER
+};
+
+void __i915_gem_object_put_pages(struct drm_i915_gem_object *obj,
+				 enum i915_mm_subclass subclass);
 void __i915_gem_object_invalidate(struct drm_i915_gem_object *obj);
 
 enum i915_map_type {