rbtree: Split out the rbtree type definitions into <linux/rbtree_types.h>

So we have this header dependency problem on RT:

 - <linux/rtmutex.h> needs the definition of 'struct rb_root_cached'.
 - <linux/rbtree.h> includes <linux/kernel.h>, which includes <linux/spinlock.h>.

That works nicely for non-RT enabled kernels, but on RT enabled kernels
spinlocks are based on rtmutexes, which creates another circular header
dependency, as <linux/spinlocks.h> will require <linux/rtmutex.h>.

Split out the type definitions and move them into their own header file so
the rtmutex header can include just those.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211303.542123501@linutronix.de

include/linux/rbtree.h

@@ -17,24 +17,14 @@
 #ifndef	_LINUX_RBTREE_H
 #define	_LINUX_RBTREE_H
 
+#include <linux/rbtree_types.h>
+
 #include <linux/kernel.h>
 #include <linux/stddef.h>
 #include <linux/rcupdate.h>
 
-struct rb_node {
-	unsigned long  __rb_parent_color;
-	struct rb_node *rb_right;
-	struct rb_node *rb_left;
-} __attribute__((aligned(sizeof(long))));
-    /* The alignment might seem pointless, but allegedly CRIS needs it */
-
-struct rb_root {
-	struct rb_node *rb_node;
-};
-
 #define rb_parent(r)   ((struct rb_node *)((r)->__rb_parent_color & ~3))
 
-#define RB_ROOT	(struct rb_root) { NULL, }
 #define	rb_entry(ptr, type, member) container_of(ptr, type, member)
 
 #define RB_EMPTY_ROOT(root)  (READ_ONCE((root)->rb_node) == NULL)
@@ -112,23 +102,6 @@ static inline void rb_link_node_rcu(struct rb_node *node, struct rb_node *parent
 			typeof(*pos), field); 1; }); \
 	     pos = n)
 
-/*
- * Leftmost-cached rbtrees.
- *
- * We do not cache the rightmost node based on footprint
- * size vs number of potential users that could benefit
- * from O(1) rb_last(). Just not worth it, users that want
- * this feature can always implement the logic explicitly.
- * Furthermore, users that want to cache both pointers may
- * find it a bit asymmetric, but that's ok.
- */
-struct rb_root_cached {
-	struct rb_root rb_root;
-	struct rb_node *rb_leftmost;
-};
-
-#define RB_ROOT_CACHED (struct rb_root_cached) { {NULL, }, NULL }
-
 /* Same as rb_first(), but O(1) */
 #define rb_first_cached(root) (root)->rb_leftmost
 

include/linux/rbtree_types.h

+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef _LINUX_RBTREE_TYPES_H
+#define _LINUX_RBTREE_TYPES_H
+
+struct rb_node {
+	unsigned long  __rb_parent_color;
+	struct rb_node *rb_right;
+	struct rb_node *rb_left;
+} __attribute__((aligned(sizeof(long))));
+/* The alignment might seem pointless, but allegedly CRIS needs it */
+
+struct rb_root {
+	struct rb_node *rb_node;
+};
+
+/*
+ * Leftmost-cached rbtrees.
+ *
+ * We do not cache the rightmost node based on footprint
+ * size vs number of potential users that could benefit
+ * from O(1) rb_last(). Just not worth it, users that want
+ * this feature can always implement the logic explicitly.
+ * Furthermore, users that want to cache both pointers may
+ * find it a bit asymmetric, but that's ok.
+ */
+struct rb_root_cached {
+	struct rb_root rb_root;
+	struct rb_node *rb_leftmost;
+};
+
+#define RB_ROOT (struct rb_root) { NULL, }
+#define RB_ROOT_CACHED (struct rb_root_cached) { {NULL, }, NULL }
+
+#endif