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, 2 insertions, 2 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem_shrinker.c b/drivers/gpu/drm/i915/i915_gem_shrinker.c
index 0993afc0e725..f988652f1e26 100644
--- a/drivers/gpu/drm/i915/i915_gem_shrinker.c
+++ b/drivers/gpu/drm/i915/i915_gem_shrinker.c
@@ -111,7 +111,7 @@ static bool can_release_pages(struct drm_i915_gem_object *obj)
 static bool unsafe_drop_pages(struct drm_i915_gem_object *obj)
 {
 	if (i915_gem_object_unbind(obj) == 0)
-		__i915_gem_object_put_pages(obj);
+		__i915_gem_object_put_pages(obj, I915_MM_SHRINKER);
 	return !READ_ONCE(obj->mm.pages);
 }
 
@@ -225,7 +225,7 @@ i915_gem_shrink(struct drm_i915_private *dev_priv,
 			if (unsafe_drop_pages(obj)) {
 				/* May arrive from get_pages on another bo */
 				mutex_lock_nested(&obj->mm.lock,
-						  SINGLE_DEPTH_NESTING);
+						  I915_MM_SHRINKER);
 				if (!obj->mm.pages) {
 					__i915_gem_object_invalidate(obj);
 					list_del_init(&obj->global_list);