Index: sys/sys/tree.h
===================================================================
--- sys/sys/tree.h
+++ sys/sys/tree.h
@@ -340,6 +340,7 @@
 #define RB_RED_MASK			((__uintptr_t)3)
 #define RB_FLIP_LEFT(elm, field)	(RB_BITS(elm, field) ^= RB_RED_L)
 #define RB_FLIP_RIGHT(elm, field)	(RB_BITS(elm, field) ^= RB_RED_R)
+#define RB_FLIP_ALL(elm, field)		(RB_BITS(elm, field) ^= RB_RED_MASK)
 #define RB_RED_LEFT(elm, field)		((RB_BITS(elm, field) & RB_RED_L) != 0)
 #define RB_RED_RIGHT(elm, field)	((RB_BITS(elm, field) & RB_RED_R) != 0)
 #define RB_PARENT(elm, field)		((__typeof(RB_UP(elm, field)))	\
@@ -477,11 +478,12 @@
 				continue;				\
 			}						\
 			if (!RB_RED_RIGHT(elm, field)) {		\
-				RB_FLIP_LEFT(elm, field);		\
 				RB_ROTATE_LEFT(head, elm, child, field);\
 				if (RB_RED_LEFT(child, field))		\
-					RB_FLIP_RIGHT(elm, field);	\
-				else if (RB_RED_RIGHT(child, field))	\
+					RB_FLIP_ALL(elm, field);	\
+				else					\
+					RB_FLIP_LEFT(elm, field);	\
+				if (RB_RED_RIGHT(child, field))		\
 					RB_FLIP_LEFT(parent, field);	\
 				elm = child;				\
 			}						\
@@ -497,11 +499,12 @@
 				continue;				\
 			}						\
 			if (!RB_RED_LEFT(elm, field)) {			\
-				RB_FLIP_RIGHT(elm, field);		\
 				RB_ROTATE_RIGHT(head, elm, child, field);\
 				if (RB_RED_RIGHT(child, field))		\
-					RB_FLIP_LEFT(elm, field);	\
-				else if (RB_RED_LEFT(child, field))	\
+					RB_FLIP_ALL(elm, field);	\
+				else					\
+					RB_FLIP_RIGHT(elm, field);	\
+				if (RB_RED_LEFT(child, field))		\
 					RB_FLIP_RIGHT(parent, field);	\
 				elm = child;				\
 			}						\
@@ -538,23 +541,30 @@
 				continue;				\
 			}						\
 			sib = RB_RIGHT(parent, field);			\
-			if ((~RB_BITS(sib, field) & RB_RED_MASK) == 0) {\
-				RB_BITS(sib, field) &= ~RB_RED_MASK;	\
+			switch (RB_BITS(sib, field) & RB_RED_MASK) {	\
+			case RB_RED_MASK:				\
+				RB_FLIP_ALL(sib, field);		\
 				elm = parent;				\
 				continue;				\
-			}						\
-			RB_FLIP_RIGHT(sib, field);			\
-			if (RB_RED_LEFT(sib, field))			\
-				RB_FLIP_LEFT(parent, field);		\
-			else if (!RB_RED_RIGHT(sib, field)) {		\
-				RB_FLIP_LEFT(parent, field);		\
+			case RB_RED_R:					\
 				RB_ROTATE_RIGHT(head, sib, elm, field);	\
-				if (RB_RED_RIGHT(elm, field))		\
-					RB_FLIP_LEFT(sib, field);	\
 				if (RB_RED_LEFT(elm, field))		\
-					RB_FLIP_RIGHT(parent, field);	\
+					RB_FLIP_ALL(parent, field);	\
+				else					\
+					RB_FLIP_LEFT(parent, field);	\
+				if (RB_RED_RIGHT(elm, field))		\
+					RB_FLIP_ALL(sib, field);	\
+				else					\
+					RB_FLIP_RIGHT(sib, field);	\
 				RB_BITS(elm, field) |= RB_RED_MASK;	\
 				sib = elm;				\
+				break;					\
+			case RB_RED_L:					\
+				RB_FLIP_LEFT(parent, field);		\
+				/* fallthrough - see footnote[1] */	\
+			default:					\
+				RB_FLIP_RIGHT(sib, field);		\
+				break;					\
 			}						\
 			RB_ROTATE_LEFT(head, parent, sib, field);	\
 		} else {						\
@@ -568,26 +578,40 @@
 				continue;				\
 			}						\
 			sib = RB_LEFT(parent, field);			\
-			if ((~RB_BITS(sib, field) & RB_RED_MASK) == 0) {\
-				RB_BITS(sib, field) &= ~RB_RED_MASK;	\
+			switch (RB_BITS(sib, field) & RB_RED_MASK) {	\
+			case RB_RED_MASK:				\
+				RB_FLIP_ALL(sib, field);		\
 				elm = parent;				\
 				continue;				\
-			}						\
-			RB_FLIP_LEFT(sib, field);			\
-			if (RB_RED_RIGHT(sib, field))			\
-				RB_FLIP_RIGHT(parent, field);		\
-			else if (!RB_RED_LEFT(sib, field)) {		\
-				RB_FLIP_RIGHT(parent, field);		\
+			case RB_RED_L:					\
 				RB_ROTATE_LEFT(head, sib, elm, field);	\
-				if (RB_RED_LEFT(elm, field))		\
-					RB_FLIP_RIGHT(sib, field);	\
 				if (RB_RED_RIGHT(elm, field))		\
-					RB_FLIP_LEFT(parent, field);	\
+					RB_FLIP_ALL(parent, field);	\
+				else					\
+					RB_FLIP_RIGHT(parent, field);	\
+				if (RB_RED_LEFT(elm, field))		\
+					RB_FLIP_ALL(sib, field);	\
+				else					\
+					RB_FLIP_LEFT(sib, field);	\
 				RB_BITS(elm, field) |= RB_RED_MASK;	\
 				sib = elm;				\
+				break;					\
+			case RB_RED_R:					\
+				RB_FLIP_RIGHT(parent, field);		\
+				/* fallthrough - see footnote [1] */	\
+			default:					\
+				RB_FLIP_LEFT(sib, field);		\
+				break;					\
 			}						\
 			RB_ROTATE_RIGHT(head, parent, sib, field);	\
 		}							\
+		/*							\
+		 * [1] - In this case the HST paper, figure 3, has	\
+		 * parent with one higher rank, and then reduces the	\
+		 * rank if parent has become a leaf.  This		\
+		 * implementation always has the parent in its new	\
+		 * position with lower rank, to avoid the leaf check.	\
+		 */							\
 		break;							\
 	} while ((parent = RB_PARENT(elm, field)) != NULL);		\
 }