[PATCH] lib/rbtree,drm/mm: Add rbtree_replace_node_cached()

[Chris Wilson <chris@chris-wilson.co.uk>]

Add a variant of rbtree_replace_node() that maintains the leftmost
cache of struct rbtree_root_cached when replacing nodes within the
rbtree.

As drm_mm is the only rb_replace_node() being used on an interval tree,
the mistake looks fairly self-contained. Furthermore the only user of
drm_mm_replace_node() is its testsuite...

Fixes: f808c13fd373 ("lib/interval_tree: fast overlap detection")
Testcase: igt/drm_mm/replace
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Davidlohr Bueso <dbueso@suse.de>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20171109212435.9265-1-chris@chris-wilson.co.uk
Acked-by: Davidlohr Bueso <dbueso@suse.de>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
---
 drivers/gpu/drm/drm_mm.c |  8 +++++---
 include/linux/rbtree.h   |  2 ++
 lib/rbtree.c             | 10 ++++++++++
 3 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_mm.c b/drivers/gpu/drm/drm_mm.c
index 61a1c8ea74bc..c3c79ee6119e 100644
--- a/drivers/gpu/drm/drm_mm.c
+++ b/drivers/gpu/drm/drm_mm.c
@@ -575,21 +575,23 @@ EXPORT_SYMBOL(drm_mm_remove_node);
  */
 void drm_mm_replace_node(struct drm_mm_node *old, struct drm_mm_node *new)
 {
+	struct drm_mm *mm = old->mm;
+
 	DRM_MM_BUG_ON(!old->allocated);
 
 	*new = *old;
 
 	list_replace(&old->node_list, &new->node_list);
-	rb_replace_node(&old->rb, &new->rb, &old->mm->interval_tree.rb_root);
+	rb_replace_node_cached(&old->rb, &new->rb, &mm->interval_tree);
 
 	if (drm_mm_hole_follows(old)) {
 		list_replace(&old->hole_stack, &new->hole_stack);
 		rb_replace_node(&old->rb_hole_size,
 				&new->rb_hole_size,
-				&old->mm->holes_size);
+				&mm->holes_size);
 		rb_replace_node(&old->rb_hole_addr,
 				&new->rb_hole_addr,
-				&old->mm->holes_addr);
+				&mm->holes_addr);
 	}
 
 	old->allocated = false;
diff --git a/include/linux/rbtree.h b/include/linux/rbtree.h
index d574361943ea..fcbeed4053ef 100644
--- a/include/linux/rbtree.h
+++ b/include/linux/rbtree.h
@@ -99,6 +99,8 @@ extern void rb_replace_node(struct rb_node *victim, struct rb_node *new,
 			    struct rb_root *root);
 extern void rb_replace_node_rcu(struct rb_node *victim, struct rb_node *new,
 				struct rb_root *root);
+extern void rb_replace_node_cached(struct rb_node *victim, struct rb_node *new,
+				   struct rb_root_cached *root);
 
 static inline void rb_link_node(struct rb_node *node, struct rb_node *parent,
 				struct rb_node **rb_link)
diff --git a/lib/rbtree.c b/lib/rbtree.c
index ba4a9d165f1b..d3ff682fd4b8 100644
--- a/lib/rbtree.c
+++ b/lib/rbtree.c
@@ -603,6 +603,16 @@ void rb_replace_node(struct rb_node *victim, struct rb_node *new,
 }
 EXPORT_SYMBOL(rb_replace_node);
 
+void rb_replace_node_cached(struct rb_node *victim, struct rb_node *new,
+			    struct rb_root_cached *root)
+{
+	rb_replace_node(victim, new, &root->rb_root);
+
+	if (root->rb_leftmost == victim)
+		root->rb_leftmost = new;
+}
+EXPORT_SYMBOL(rb_replace_node_cached);
+
 void rb_replace_node_rcu(struct rb_node *victim, struct rb_node *new,
 			 struct rb_root *root)
 {
-- 
2.15.0