From: Kaitao Cheng <chengkaitao@kylinos.cn>

Extend the refcounted_kptr test: add a node to both an rbtree and a
list, retrieve the node from the rbtree to obtain the node pointer,
then add a new node after the first in the list, and finally use
bpf_list_del to remove both nodes.

The test asserts that the list is non-empty after insert, asserts the
first and last nodes after bpf_list_add, and asserts that the list is
empty after removing both nodes.

To verify the validity of bpf_list_del/add, the test also expects the
verifier to reject calls to bpf_list_del/add made without holding the
spin_lock.

Signed-off-by: Kaitao Cheng <chengkaitao@kylinos.cn>
---
 .../testing/selftests/bpf/bpf_experimental.h  |  39 ++++
 .../selftests/bpf/progs/refcounted_kptr.c     | 182 ++++++++++++++++++
 2 files changed, 221 insertions(+)

diff --git a/tools/testing/selftests/bpf/bpf_experimental.h b/tools/testing/selftests/bpf/bpf_experimental.h
index 4b7210c318dd..d5f42ed69166 100644
--- a/tools/testing/selftests/bpf/bpf_experimental.h
+++ b/tools/testing/selftests/bpf/bpf_experimental.h
@@ -99,6 +99,45 @@ extern struct bpf_list_node *bpf_list_pop_front(struct bpf_list_head *head) __ks
  */
 extern struct bpf_list_node *bpf_list_pop_back(struct bpf_list_head *head) __ksym;
 
+/* Description
+ *	Remove 'node' from the BPF linked list with head 'head'.
+ *	The node must be in the list. Caller receives ownership of the
+ *	removed node and must release it with bpf_obj_drop.
+ * Returns
+ *	Pointer to the removed bpf_list_node, or NULL if 'node' is NULL
+ *	or not in the list.
+ */
+extern struct bpf_list_node *bpf_list_del(struct bpf_list_head *head,
+					  struct bpf_list_node *node) __ksym;
+
+/* Description
+ *	Insert 'new' after 'prev' in the BPF linked list with head 'head'.
+ *	The bpf_spin_lock protecting the list must be held. 'prev' must already
+ *	be in that list; 'new' must not be in any list. The 'meta' and 'off'
+ *	parameters are rewritten by the verifier, no need for BPF programs to
+ *	set them.
+ * Returns
+ *	0 on success, -EINVAL if head is NULL, prev is not in the list with head,
+ *	or new is already in a list.
+ */
+extern int bpf_list_add_impl(struct bpf_list_head *head, struct bpf_list_node *new,
+			     struct bpf_list_node *prev, void *meta, __u64 off) __ksym;
+
+/* Convenience macro to wrap over bpf_list_add_impl */
+#define bpf_list_add(head, new, prev) bpf_list_add_impl(head, new, prev, NULL, 0)
+
+/* Description
+ *	Return true if 'node' is the first (when 'is_first' is true) or the last
+ *	(when 'is_first' is false) node in the list with head 'head'.
+ */
+extern bool bpf_list_node_is_edge(struct bpf_list_head *head,
+				  struct bpf_list_node *node, bool is_first) __ksym;
+
+/* Description
+ *	Return true if the list with head 'head' has no entries.
+ */
+extern bool bpf_list_empty(struct bpf_list_head *head) __ksym;
+
 /* Description
  *	Remove 'node' from rbtree with root 'root'
  * Returns
diff --git a/tools/testing/selftests/bpf/progs/refcounted_kptr.c b/tools/testing/selftests/bpf/progs/refcounted_kptr.c
index 1aca85d86aeb..aca201f9fb56 100644
--- a/tools/testing/selftests/bpf/progs/refcounted_kptr.c
+++ b/tools/testing/selftests/bpf/progs/refcounted_kptr.c
@@ -367,6 +367,188 @@ long insert_rbtree_and_stash__del_tree_##rem_tree(void *ctx)		\
 INSERT_STASH_READ(true, "insert_stash_read: remove from tree");
 INSERT_STASH_READ(false, "insert_stash_read: don't remove from tree");
 
+/* Insert one node in tree and list, remove it from tree, add a second node
+ * after it with bpf_list_add, check bpf_list_node_is_edge/empty, then
+ * remove both nodes from list via bpf_list_del.
+ */
+SEC("tc")
+__description("list_add_del_and_check: test bpf_list_add/del/is_first/is_last/empty")
+__success __retval(0)
+long list_add_del_and_check(void *ctx)
+{
+	long err = 0;
+	struct bpf_rb_node *rb;
+	struct bpf_list_node *l, *l_1;
+	struct node_data *n, *n_1, *m_1;
+
+	err = __insert_in_tree_and_list(&head, &root, &lock);
+	if (err)
+		return err;
+
+	bpf_spin_lock(&lock);
+	if (bpf_list_empty(&head)) {
+		bpf_spin_unlock(&lock);
+		return -7;
+	}
+
+	rb = bpf_rbtree_first(&root);
+	if (!rb) {
+		bpf_spin_unlock(&lock);
+		return -4;
+	}
+
+	rb = bpf_rbtree_remove(&root, rb);
+	bpf_spin_unlock(&lock);
+	if (!rb)
+		return -5;
+
+	n = container_of(rb, struct node_data, r);
+	n_1 = bpf_obj_new(typeof(*n_1));
+	if (!n_1) {
+		bpf_obj_drop(n);
+		return -1;
+	}
+	m_1 = bpf_refcount_acquire(n_1);
+	if (!m_1) {
+		bpf_obj_drop(n);
+		bpf_obj_drop(n_1);
+		return -1;
+	}
+
+	bpf_spin_lock(&lock);
+	if (bpf_list_add(&head, &n_1->l, &n->l)) {
+		bpf_spin_unlock(&lock);
+		bpf_obj_drop(n);
+		bpf_obj_drop(m_1);
+		return -8;
+	}
+
+	if (!bpf_list_node_is_edge(&head, &n->l, true) ||
+	    !bpf_list_node_is_edge(&head, &m_1->l, false)) {
+		bpf_spin_unlock(&lock);
+		bpf_obj_drop(n);
+		bpf_obj_drop(m_1);
+		return -9;
+	}
+
+	l = bpf_list_del(&head, &n->l);
+	l_1 = bpf_list_del(&head, &m_1->l);
+	bpf_spin_unlock(&lock);
+	bpf_obj_drop(n);
+	bpf_obj_drop(m_1);
+
+	if (l)
+		bpf_obj_drop(container_of(l, struct node_data, l));
+	else
+		err = -6;
+
+	if (l_1)
+		bpf_obj_drop(container_of(l_1, struct node_data, l));
+	else
+		err = -6;
+
+	bpf_spin_lock(&lock);
+	if (!bpf_list_empty(&head))
+		err = -7;
+	bpf_spin_unlock(&lock);
+	return err;
+}
+
+SEC("?tc")
+__failure __msg("bpf_spin_lock at off=32 must be held for bpf_list_head")
+long list_del_without_lock_fail(void *ctx)
+{
+	struct bpf_rb_node *rb;
+	struct bpf_list_node *l;
+	struct node_data *n;
+
+	bpf_spin_lock(&lock);
+	rb = bpf_rbtree_first(&root);
+	if (!rb) {
+		bpf_spin_unlock(&lock);
+		return -4;
+	}
+
+	rb = bpf_rbtree_remove(&root, rb);
+	bpf_spin_unlock(&lock);
+	if (!rb)
+		return -5;
+
+	n = container_of(rb, struct node_data, r);
+	l = bpf_list_del(&head, &n->l);
+	bpf_obj_drop(n);
+	if (!l)
+		return -6;
+
+	bpf_obj_drop(container_of(l, struct node_data, l));
+	return 0;
+}
+
+SEC("?tc")
+__failure __msg("bpf_spin_lock at off=32 must be held for bpf_list_head")
+long list_add_without_lock_fail(void *ctx)
+{
+	long err = 0;
+	struct bpf_rb_node *rb;
+	struct bpf_list_node *l, *l_1;
+	struct node_data *n, *n_1, *m_1;
+
+	err = __insert_in_tree_and_list(&head, &root, &lock);
+	if (err)
+		return err;
+
+	bpf_spin_lock(&lock);
+	rb = bpf_rbtree_first(&root);
+	if (!rb) {
+		bpf_spin_unlock(&lock);
+		return -4;
+	}
+
+	rb = bpf_rbtree_remove(&root, rb);
+	bpf_spin_unlock(&lock);
+	if (!rb)
+		return -5;
+
+	n = container_of(rb, struct node_data, r);
+	n_1 = bpf_obj_new(typeof(*n_1));
+	if (!n_1) {
+		bpf_obj_drop(n);
+		return -1;
+	}
+	m_1 = bpf_refcount_acquire(n_1);
+	if (!m_1) {
+		bpf_obj_drop(n);
+		bpf_obj_drop(n_1);
+		return -1;
+	}
+
+	/* Intentionally no lock: verifier should reject bpf_list_add without lock */
+	if (bpf_list_add(&head, &n_1->l, &n->l)) {
+		bpf_obj_drop(n);
+		bpf_obj_drop(m_1);
+		return -8;
+	}
+
+	bpf_spin_lock(&lock);
+	l = bpf_list_del(&head, &n->l);
+	l_1 = bpf_list_del(&head, &m_1->l);
+	bpf_spin_unlock(&lock);
+	bpf_obj_drop(n);
+	bpf_obj_drop(m_1);
+
+	if (l)
+		bpf_obj_drop(container_of(l, struct node_data, l));
+	else
+		err = -6;
+
+	if (l_1)
+		bpf_obj_drop(container_of(l_1, struct node_data, l));
+	else
+		err = -6;
+
+	return err;
+}
+
 SEC("tc")
 __success
 long rbtree_refcounted_node_ref_escapes(void *ctx)
-- 
2.50.1 (Apple Git-155)

On Wed, 4 Mar 2026 at 15:51, Chengkaitao <pilgrimtao@gmail.com> wrote:
>
> From: Kaitao Cheng <chengkaitao@kylinos.cn>
>
> Extend the refcounted_kptr test: add a node to both an rbtree and a
> list, retrieve the node from the rbtree to obtain the node pointer,
> then add a new node after the first in the list, and finally use
> bpf_list_del to remove both nodes.
>
> The test asserts that the list is non-empty after insert, asserts the
> first and last nodes after bpf_list_add, and asserts that the list is
> empty after removing both nodes.
>
> To verify the validity of bpf_list_del/add, the test also expects the
> verifier to reject calls to bpf_list_del/add made without holding the
> spin_lock.
>
> Signed-off-by: Kaitao Cheng <chengkaitao@kylinos.cn>
> ---

No reply to or feedback addressed from
https://lore.kernel.org/all/87342fzjq0.fsf@gmail.com.
Please don't respin without acting on it, or explaining why you chose
to skip it.

>  .../testing/selftests/bpf/bpf_experimental.h  |  39 ++++
>  .../selftests/bpf/progs/refcounted_kptr.c     | 182 ++++++++++++++++++
>  2 files changed, 221 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/bpf_experimental.h b/tools/testing/selftests/bpf/bpf_experimental.h
> index 4b7210c318dd..d5f42ed69166 100644
> --- a/tools/testing/selftests/bpf/bpf_experimental.h
> +++ b/tools/testing/selftests/bpf/bpf_experimental.h
> @@ -99,6 +99,45 @@ extern struct bpf_list_node *bpf_list_pop_front(struct bpf_list_head *head) __ks
>   */
>  extern struct bpf_list_node *bpf_list_pop_back(struct bpf_list_head *head) __ksym;
>
> +/* Description
> + *     Remove 'node' from the BPF linked list with head 'head'.
> + *     The node must be in the list. Caller receives ownership of the
> + *     removed node and must release it with bpf_obj_drop.
> + * Returns
> + *     Pointer to the removed bpf_list_node, or NULL if 'node' is NULL
> + *     or not in the list.
> + */
> +extern struct bpf_list_node *bpf_list_del(struct bpf_list_head *head,
> +                                         struct bpf_list_node *node) __ksym;
> +
> +/* Description
> + *     Insert 'new' after 'prev' in the BPF linked list with head 'head'.
> + *     The bpf_spin_lock protecting the list must be held. 'prev' must already
> + *     be in that list; 'new' must not be in any list. The 'meta' and 'off'
> + *     parameters are rewritten by the verifier, no need for BPF programs to
> + *     set them.
> + * Returns
> + *     0 on success, -EINVAL if head is NULL, prev is not in the list with head,
> + *     or new is already in a list.
> + */
> +extern int bpf_list_add_impl(struct bpf_list_head *head, struct bpf_list_node *new,
> +                            struct bpf_list_node *prev, void *meta, __u64 off) __ksym;
> +
> +/* Convenience macro to wrap over bpf_list_add_impl */
> +#define bpf_list_add(head, new, prev) bpf_list_add_impl(head, new, prev, NULL, 0)
> +
> +/* Description
> + *     Return true if 'node' is the first (when 'is_first' is true) or the last
> + *     (when 'is_first' is false) node in the list with head 'head'.
> + */
> +extern bool bpf_list_node_is_edge(struct bpf_list_head *head,
> +                                 struct bpf_list_node *node, bool is_first) __ksym;
> +
> +/* Description
> + *     Return true if the list with head 'head' has no entries.
> + */
> +extern bool bpf_list_empty(struct bpf_list_head *head) __ksym;
> +

Except the macro, the rest can come from vmlinux.h.

>  /* Description
>   *     Remove 'node' from rbtree with root 'root'
>   * Returns
> diff --git a/tools/testing/selftests/bpf/progs/refcounted_kptr.c b/tools/testing/selftests/bpf/progs/refcounted_kptr.c
> index 1aca85d86aeb..aca201f9fb56 100644
> --- a/tools/testing/selftests/bpf/progs/refcounted_kptr.c
> +++ b/tools/testing/selftests/bpf/progs/refcounted_kptr.c
> @@ -367,6 +367,188 @@ long insert_rbtree_and_stash__del_tree_##rem_tree(void *ctx)              \
>  INSERT_STASH_READ(true, "insert_stash_read: remove from tree");
>  INSERT_STASH_READ(false, "insert_stash_read: don't remove from tree");
>
> +/* Insert one node in tree and list, remove it from tree, add a second node
> + * after it with bpf_list_add, check bpf_list_node_is_edge/empty, then
> + * remove both nodes from list via bpf_list_del.
> + */

Incorrect comment style.

> +[...]
>