[PATCH 1/2] lib/rbtree,drm/mm: Add rbtree_replace_node_cached()

[Chris Wilson]

Add a variant of rbtree_replace_node() that maintains the leftmost
cached 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 <ch...@chris-wilson.co.uk>
Cc: Davidlohr Bueso <dbu...@suse.de>
Cc: Jérôme Glisse <jgli...@redhat.com>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Joonas Lahtinen <joonas.lahti...@linux.intel.com>
Cc: Daniel Vetter <daniel.vet...@ffwll.ch>
---
 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 eb86bc3f753b..186c4e90cc1c 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

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