lib/rbtree: set successor's parent unconditionally

Both in Case 2 and 3, we exchange n and s.  This mean no matter whether
child2 is NULL or not, successor's parent should be assigned to node's.

This patch takes this step out to make it explicit and reduce the
ambiguity.

Besides, this step reduces some symbol size like rb_erase().

   KERN_CONFIG       upstream       patched
   OPT_FOR_PERF      877            870
   OPT_FOR_SIZE      635            621

Link: http://lkml.kernel.org/r/20191028021442.5450-1-richardw.yang@linux.intel.com
Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Michel Lespinasse <walken@google.com>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/rbtree_augmented.h b/include/linux/rbtree_augmented.h
index fdd421b8d9ae44e8e40874988a0a29e1c76d635b..99c42e1a74b88e21a149e2707cb68549bfb05d07 100644 (file)
--- a/include/linux/rbtree_augmented.h
+++ b/include/linux/rbtree_augmented.h
@@ -283,14 +283,13 @@ __rb_erase_augmented(struct rb_node *node, struct rb_root *root,
                __rb_change_child(node, successor, tmp, root);
 
                if (child2) {
-                       successor->__rb_parent_color = pc;
                        rb_set_parent_color(child2, parent, RB_BLACK);
                        rebalance = NULL;
                } else {
                        unsigned long pc2 = successor->__rb_parent_color;
-                       successor->__rb_parent_color = pc;
                        rebalance = __rb_is_black(pc2) ? parent : NULL;
                }
+               successor->__rb_parent_color = pc;
                tmp = successor;
        }