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  |  16 ++
 .../selftests/bpf/progs/refcounted_kptr.c     | 140 ++++++++++++++++++
 2 files changed, 156 insertions(+)

diff --git a/tools/testing/selftests/bpf/bpf_experimental.h b/tools/testing/selftests/bpf/bpf_experimental.h
index 4b7210c318dd..005ca9d84677 100644
--- a/tools/testing/selftests/bpf/bpf_experimental.h
+++ b/tools/testing/selftests/bpf/bpf_experimental.h
@@ -85,6 +85,22 @@ extern int bpf_list_push_back_impl(struct bpf_list_head *head,
 /* Convenience macro to wrap over bpf_list_push_back_impl */
 #define bpf_list_push_back(head, node) bpf_list_push_back_impl(head, node, NULL, 0)
 
+/* 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
  *	Remove the entry at the beginning of the BPF linked list.
  * Returns
diff --git a/tools/testing/selftests/bpf/progs/refcounted_kptr.c b/tools/testing/selftests/bpf/progs/refcounted_kptr.c
index 1aca85d86aeb..c2defa991acd 100644
--- a/tools/testing/selftests/bpf/progs/refcounted_kptr.c
+++ b/tools/testing/selftests/bpf/progs/refcounted_kptr.c
@@ -367,6 +367,146 @@ 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_is_first/is_last/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_node, *l_node_ref;
+	struct node_data *n_rb, *n_new, *n_new_ref;
+
+	err = __insert_in_tree_and_list(&head, &root, &lock);
+	if (err)
+		return err;
+
+	bpf_spin_lock(&lock);
+	/* Test1: bpf_list_empty */
+	if (bpf_list_empty(&head)) {
+		bpf_spin_unlock(&lock);
+		return -4;
+	}
+
+	rb = bpf_rbtree_first(&root);
+	if (!rb) {
+		bpf_spin_unlock(&lock);
+		return -5;
+	}
+
+	rb = bpf_rbtree_remove(&root, rb);
+	bpf_spin_unlock(&lock);
+	if (!rb)
+		return -6;
+
+	n_rb = container_of(rb, struct node_data, r);
+	n_new = bpf_obj_new(typeof(*n_new));
+	if (!n_new) {
+		bpf_obj_drop(n_rb);
+		return -7;
+	}
+	n_new_ref = bpf_refcount_acquire(n_new);
+	if (!n_new_ref) {
+		bpf_obj_drop(n_rb);
+		bpf_obj_drop(n_new);
+		return -8;
+	}
+
+	bpf_spin_lock(&lock);
+	/* Test2: bpf_list_add */
+	if (bpf_list_add(&head, &n_new->l, &n_rb->l)) {
+		bpf_spin_unlock(&lock);
+		bpf_obj_drop(n_rb);
+		bpf_obj_drop(n_new_ref);
+		return -9;
+	}
+
+	/* Test3: bpf_list_is_first/is_last */
+	if (!bpf_list_is_first(&head, &n_rb->l) ||
+	    !bpf_list_is_last(&head, &n_new_ref->l)) {
+		bpf_spin_unlock(&lock);
+		bpf_obj_drop(n_rb);
+		bpf_obj_drop(n_new_ref);
+		return -10;
+	}
+
+	/* Test4: bpf_list_del */
+	l_node = bpf_list_del(&head, &n_rb->l);
+	l_node_ref = bpf_list_del(&head, &n_new_ref->l);
+	bpf_spin_unlock(&lock);
+	bpf_obj_drop(n_rb);
+	bpf_obj_drop(n_new_ref);
+
+	if (l_node)
+		bpf_obj_drop(container_of(l_node, struct node_data, l));
+	else
+		err = -11;
+
+	if (l_node_ref)
+		bpf_obj_drop(container_of(l_node_ref, struct node_data, l));
+	else
+		err = -12;
+
+	bpf_spin_lock(&lock);
+	/* Test5: bpf_list_empty */
+	if (!bpf_list_empty(&head))
+		err = -13;
+	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);
+	bpf_spin_unlock(&lock);
+	if (!rb)
+		return -1;
+
+	n = container_of(rb, struct node_data, r);
+	/* Error case: delete list node without holding lock */
+	l = bpf_list_del(&head, &n->l);
+	if (!l)
+		return -2;
+	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)
+{
+	struct bpf_rb_node *rb;
+	struct bpf_list_node *l;
+	struct node_data *n;
+
+	bpf_spin_lock(&lock);
+	rb = bpf_rbtree_first(&root);
+	l = bpf_list_front(&head);
+	bpf_spin_unlock(&lock);
+	if (!rb || !l)
+		return -1;
+
+	n = container_of(l, struct node_data, l);
+	/* Error case: add list node without holding lock */
+	if (bpf_list_add(&head, &n->l, l))
+		return -2;
+
+	return 0;
+}
+
 SEC("tc")
 __success
 long rbtree_refcounted_node_ref_escapes(void *ctx)
-- 
2.50.1 (Apple Git-155)

On 8/3/26 21:46, Chengkaitao 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>
> ---
>  .../testing/selftests/bpf/bpf_experimental.h  |  16 ++
>  .../selftests/bpf/progs/refcounted_kptr.c     | 140 ++++++++++++++++++
>  2 files changed, 156 insertions(+)
> 
> diff --git a/tools/testing/selftests/bpf/bpf_experimental.h b/tools/testing/selftests/bpf/bpf_experimental.h
> index 4b7210c318dd..005ca9d84677 100644
> --- a/tools/testing/selftests/bpf/bpf_experimental.h
> +++ b/tools/testing/selftests/bpf/bpf_experimental.h
> @@ -85,6 +85,22 @@ extern int bpf_list_push_back_impl(struct bpf_list_head *head,
>  /* Convenience macro to wrap over bpf_list_push_back_impl */
>  #define bpf_list_push_back(head, node) bpf_list_push_back_impl(head, node, NULL, 0)
>  
> +/* 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
>   *	Remove the entry at the beginning of the BPF linked list.
>   * Returns
> diff --git a/tools/testing/selftests/bpf/progs/refcounted_kptr.c b/tools/testing/selftests/bpf/progs/refcounted_kptr.c
> index 1aca85d86aeb..c2defa991acd 100644
> --- a/tools/testing/selftests/bpf/progs/refcounted_kptr.c
> +++ b/tools/testing/selftests/bpf/progs/refcounted_kptr.c
> @@ -367,6 +367,146 @@ 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_is_first/is_last/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_node, *l_node_ref;
> +	struct node_data *n_rb, *n_new, *n_new_ref;
> +

Prefer inverted Christmas tree style.

> +	err = __insert_in_tree_and_list(&head, &root, &lock);
> +	if (err)
> +		return err;
> +
> +	bpf_spin_lock(&lock);
> +	/* Test1: bpf_list_empty */
> +	if (bpf_list_empty(&head)) {
> +		bpf_spin_unlock(&lock);
> +		return -4;
> +	}
> +
> +	rb = bpf_rbtree_first(&root);
> +	if (!rb) {
> +		bpf_spin_unlock(&lock);
> +		return -5;
> +	}
> +
> +	rb = bpf_rbtree_remove(&root, rb);
> +	bpf_spin_unlock(&lock);
> +	if (!rb)
> +		return -6;
> +
> +	n_rb = container_of(rb, struct node_data, r);
> +	n_new = bpf_obj_new(typeof(*n_new));
> +	if (!n_new) {
> +		bpf_obj_drop(n_rb);
> +		return -7;
> +	}
> +	n_new_ref = bpf_refcount_acquire(n_new);
> +	if (!n_new_ref) {
> +		bpf_obj_drop(n_rb);
> +		bpf_obj_drop(n_new);
> +		return -8;
> +	}
> +
> +	bpf_spin_lock(&lock);
> +	/* Test2: bpf_list_add */
> +	if (bpf_list_add(&head, &n_new->l, &n_rb->l)) {
> +		bpf_spin_unlock(&lock);
> +		bpf_obj_drop(n_rb);
> +		bpf_obj_drop(n_new_ref);
> +		return -9;
> +	}
> +
> +	/* Test3: bpf_list_is_first/is_last */
> +	if (!bpf_list_is_first(&head, &n_rb->l) ||
> +	    !bpf_list_is_last(&head, &n_new_ref->l)) {
> +		bpf_spin_unlock(&lock);
> +		bpf_obj_drop(n_rb);
> +		bpf_obj_drop(n_new_ref);
> +		return -10;
> +	}
> +
> +	/* Test4: bpf_list_del */
> +	l_node = bpf_list_del(&head, &n_rb->l);
> +	l_node_ref = bpf_list_del(&head, &n_new_ref->l);
> +	bpf_spin_unlock(&lock);
> +	bpf_obj_drop(n_rb);
> +	bpf_obj_drop(n_new_ref);
> +
> +	if (l_node)
> +		bpf_obj_drop(container_of(l_node, struct node_data, l));
> +	else
> +		err = -11;
> +
> +	if (l_node_ref)
> +		bpf_obj_drop(container_of(l_node_ref, struct node_data, l));
> +	else
> +		err = -12;
> +
> +	bpf_spin_lock(&lock);
> +	/* Test5: bpf_list_empty */
> +	if (!bpf_list_empty(&head))
> +		err = -13;
> +	bpf_spin_unlock(&lock);
> +	return err;
> +}
> +

Could you split this test into 5 tests?

More easily to understand the purpose of tests with fewer lines.

Thanks,
Leon

> +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);
> +	bpf_spin_unlock(&lock);
> +	if (!rb)
> +		return -1;
> +
> +	n = container_of(rb, struct node_data, r);
> +	/* Error case: delete list node without holding lock */
> +	l = bpf_list_del(&head, &n->l);
> +	if (!l)
> +		return -2;
> +	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)
> +{
> +	struct bpf_rb_node *rb;
> +	struct bpf_list_node *l;
> +	struct node_data *n;
> +
> +	bpf_spin_lock(&lock);
> +	rb = bpf_rbtree_first(&root);
> +	l = bpf_list_front(&head);
> +	bpf_spin_unlock(&lock);
> +	if (!rb || !l)
> +		return -1;
> +
> +	n = container_of(l, struct node_data, l);
> +	/* Error case: add list node without holding lock */
> +	if (bpf_list_add(&head, &n->l, l))
> +		return -2;
> +
> +	return 0;
> +}
> +
>  SEC("tc")
>  __success
>  long rbtree_refcounted_node_ref_escapes(void *ctx)

On Sun, Mar 8, 2026 at 11:44 PM Leon Hwang <leon.hwang@linux.dev> wrote:
>
> > +long list_add_del_and_check(void *ctx)
> > +{
> > +     long err = 0;
> > +     struct bpf_rb_node *rb;
> > +     struct bpf_list_node *l_node, *l_node_ref;
> > +     struct node_data *n_rb, *n_new, *n_new_ref;
> > +
>
> Prefer inverted Christmas tree style.

Just to clarify.

This is not a requirement, but "nice to have" in a new code
if it doesn't interfere with logical declaration of variables.

> diff --git a/tools/testing/selftests/bpf/bpf_experimental.h b/tools/testing/selftests/bpf/bpf_experimental.h
> --- a/tools/testing/selftests/bpf/bpf_experimental.h
> +++ b/tools/testing/selftests/bpf/bpf_experimental.h
> @@ -86,6 +86,22 @@ #define bpf_list_push_front(head, node) bpf_list_push_front_impl(head, node, NULL, 0)
>  #define bpf_list_push_back(head, node) bpf_list_push_back_impl(head, node, NULL, 0)
>
> +/* Description
> + *	Insert 'new' after 'prev' in the BPF linked list with head 'head'.

[ ... ]

> +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)

This adds the extern declaration for bpf_list_add_impl, but the test
also calls bpf_list_del(), bpf_list_empty(), bpf_list_is_first(),
bpf_list_is_last(), and bpf_list_front(). Are the extern __ksym
declarations for those five kfuncs missing from this header?

The v6 of this series added all the declarations here (39 lines), but
v7 reduced it to just bpf_list_add_impl. The btf_dump code in libbpf
(btf_dump.c) treats BTF_KIND_FUNC as unsupported data and does not emit
function prototypes into vmlinux.h:

tools/lib/bpf/btf_dump.c:btf_dump_emit_type_decl_via_under() {
    ...
    case BTF_KIND_FUNC:
    case BTF_KIND_FUNC_PROTO:
        err = btf_dump_unsupported_data(d, t, id);
    ...
}

Without declarations, the BPF program will not compile. The existing
kfuncs in this file (bpf_list_push_front_impl, bpf_list_pop_front,
bpf_list_pop_back, etc.) all have explicit extern __ksym declarations
here. Would something like the following be needed?

    extern struct bpf_list_node *bpf_list_del(struct bpf_list_head *head,
                                              struct bpf_list_node *node) __ksym;
    extern bool bpf_list_is_first(struct bpf_list_head *head,
                                  struct bpf_list_node *node) __ksym;
    extern bool bpf_list_is_last(struct bpf_list_head *head,
                                 struct bpf_list_node *node) __ksym;
    extern bool bpf_list_empty(struct bpf_list_head *head) __ksym;
    extern struct bpf_list_node *bpf_list_front(struct bpf_list_head *head) __ksym;


---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/22822524869