Subject: Re: linux-next: build failure after merge of the mm-nonmm-unstable tree

From: Andrew Morton <[email-masked]>
Date: Wed, 19 Nov 2025 15:48:24 -0800

On Thu, 20 Nov 2025 10:14:40 +1100 Stephen Rothwell <[email-masked]> wrote:

> Hi all,
> 
> On Mon, 17 Nov 2025 10:23:10 +1100 Stephen Rothwell <[email-masked]> wrote:
> >
> > After merging the mm-nonmm-unstable tree, today's linux-next build
> > (x86_64 allmodconfig) failed like this:
> > 
> > error[E0425]: cannot find function `rb_first` in crate `bindings`
> >    --> rust/kernel/rbtree.rs:209:42  
> >     |
> > 209 |                 next: unsafe { bindings::rb_first(&self.root) },
> >     |                                          ^^^^^^^^ not found in `bindings`
> > 
> > error[E0425]: cannot find function `rb_first` in crate `bindings`
> >    --> rust/kernel/rbtree.rs:224:42  
> >     |
> > 224 |                 next: unsafe { bindings::rb_first(from_mut(&mut self.root)) },
> >     |                                          ^^^^^^^^ not found in `bindings`
> > 
> > error[E0425]: cannot find function `rb_first` in crate `bindings`
> >    --> rust/kernel/rbtree.rs:249:42  
> >     |
> > 249 |         let current = unsafe { bindings::rb_first(root) };
> >     |                                          ^^^^^^^^ not found in `bindings`
> > 
> > error[E0425]: cannot find function `rb_last` in crate `bindings`
> >      --> rust/kernel/rbtree.rs:264:42  
> >       |
> > 264   |         let current = unsafe { bindings::rb_last(root) };
> >       |                                          ^^^^^^^ help: a function with a similar name exists: `sg_last`
> >       |
> >      ::: rust/bindings/bindings_generated.rs:90155:5
> >       |
> > 90155 |     pub fn sg_last(s: *mut scatterlist, arg1: ffi::c_uint) -> *mut scatterlist;
> >       |     --------------------------------------------------------------------------- similarly named function `sg_last` defined here
> > 
> > error: aborting due to 4 previous errors
> > 
> > For more information about this error, try `rustc --explain E0425`.
> > 
> > Caused by commit
> > 
> >   84aa8c5fc414 ("rbtree: inline rb_first()")
> > 
> > I have reverted that commit and the following one for today.
> 
> I am still reverting those commits.

Thanks, I'll disable them for now.

Alice, can you please help us with a fix?  Simple patch follows:

--- a/include/linux/rbtree.h~rbtree-inline-rb_first
+++ a/include/linux/rbtree.h
@@ -43,7 +43,21 @@ extern void rb_erase(struct rb_node *, s
 /* Find logical next and previous nodes in a tree */
 extern struct rb_node *rb_next(const struct rb_node *);
 extern struct rb_node *rb_prev(const struct rb_node *);
-extern struct rb_node *rb_first(const struct rb_root *);
+
+/*
+ * This function returns the first node (in sort order) of the tree.
+ */
+static inline struct rb_node *rb_first(const struct rb_root *root)
+{
+	struct rb_node	*n;
+
+	n = root->rb_node;
+	if (!n)
+		return NULL;
+	while (n->rb_left)
+		n = n->rb_left;
+	return n;
+}
 extern struct rb_node *rb_last(const struct rb_root *);
 
 /* Postorder iteration - always visit the parent after its children */
--- a/lib/rbtree.c~rbtree-inline-rb_first
+++ a/lib/rbtree.c
@@ -460,22 +460,6 @@ void __rb_insert_augmented(struct rb_nod
 }
 EXPORT_SYMBOL(__rb_insert_augmented);
 
-/*
- * This function returns the first node (in sort order) of the tree.
- */
-struct rb_node *rb_first(const struct rb_root *root)
-{
-	struct rb_node	*n;
-
-	n = root->rb_node;
-	if (!n)
-		return NULL;
-	while (n->rb_left)
-		n = n->rb_left;
-	return n;
-}
-EXPORT_SYMBOL(rb_first);
-
 struct rb_node *rb_last(const struct rb_root *root)
 {
 	struct rb_node	*n;
_