[PATCH 0/2] bpf: Introduce the bpf_list_del API

[PATCH 0/2] bpf: Introduce the bpf_list_del API

[Chengkaitao]

From: Kaitao Cheng <chengkaitao@kylinos.cn>

In BPF, a list can only be used to implement a stack structure.
Due to an incomplete API set, only FIFO or LIFO operations are
supported.

We propose introducing the bpf_list_del API, which allows users
to directly remove a node from the list if the node pointer is
obtained beforehand. This patch enhances the BPF list API,
making it more list-like.

Kaitao Cheng (2):
  bpf: Introduce the bpf_list_del kfunc.
  selftests/bpf: Add test cases for bpf_list_del

 kernel/bpf/helpers.c                          | 19 +++++++++
 kernel/bpf/verifier.c                         |  6 ++-
 .../testing/selftests/bpf/bpf_experimental.h  | 11 +++++
 .../selftests/bpf/progs/refcounted_kptr.c     | 41 +++++++++++++++++++
 4 files changed, 76 insertions(+), 1 deletion(-)

-- 
2.50.1 (Apple Git-155)

[PATCH 1/2] bpf: Introduce the bpf_list_del kfunc.

[Chengkaitao]

From: Kaitao Cheng <chengkaitao@kylinos.cn>

If a user holds ownership of a node in the middle of a list, they
can directly remove it from the list without strictly adhering to
deletion rules from the head or tail.

This is typically paired with bpf_refcount. After calling
bpf_list_del, it is generally necessary to drop the reference to
the list node twice to prevent reference count leaks.

Signed-off-by: Kaitao Cheng <chengkaitao@kylinos.cn>
---
 kernel/bpf/helpers.c  | 19 +++++++++++++++++++
 kernel/bpf/verifier.c |  6 +++++-
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index db72b96f9c8c..44d9b9ea8d40 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2388,6 +2388,24 @@ __bpf_kfunc struct bpf_list_node *bpf_list_pop_back(struct bpf_list_head *head)
 	return __bpf_list_del(head, true);
 }
 
+__bpf_kfunc struct bpf_list_node *bpf_list_del(struct bpf_list_head *head,
+					       struct bpf_list_node *node)
+{
+	struct bpf_list_node_kern *knode = (struct bpf_list_node_kern *)node;
+	struct list_head *h = (void *)head;
+
+	if (unlikely(!knode))
+		return NULL;
+
+	if (WARN_ON_ONCE(READ_ONCE(knode->owner) != h))
+		return NULL;
+
+	list_del_init(&knode->list_head);
+	WRITE_ONCE(knode->owner, NULL);
+
+	return node;
+}
+
 __bpf_kfunc struct bpf_list_node *bpf_list_front(struct bpf_list_head *head)
 {
 	struct list_head *h = (struct list_head *)head;
@@ -4404,6 +4422,7 @@ BTF_ID_FLAGS(func, bpf_list_push_front_impl)
 BTF_ID_FLAGS(func, bpf_list_push_back_impl)
 BTF_ID_FLAGS(func, bpf_list_pop_front, KF_ACQUIRE | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_list_pop_back, KF_ACQUIRE | KF_RET_NULL)
+BTF_ID_FLAGS(func, bpf_list_del, KF_ACQUIRE | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_list_front, KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_list_back, KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_task_acquire, KF_ACQUIRE | KF_RCU | KF_RET_NULL)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 50cb4956e5bb..dff6cc8912e4 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -12345,6 +12345,7 @@ enum special_kfunc_type {
 	KF_bpf_list_push_back_impl,
 	KF_bpf_list_pop_front,
 	KF_bpf_list_pop_back,
+	KF_bpf_list_del,
 	KF_bpf_list_front,
 	KF_bpf_list_back,
 	KF_bpf_cast_to_kern_ctx,
@@ -12399,6 +12400,7 @@ BTF_ID(func, bpf_list_push_front_impl)
 BTF_ID(func, bpf_list_push_back_impl)
 BTF_ID(func, bpf_list_pop_front)
 BTF_ID(func, bpf_list_pop_back)
+BTF_ID(func, bpf_list_del)
 BTF_ID(func, bpf_list_front)
 BTF_ID(func, bpf_list_back)
 BTF_ID(func, bpf_cast_to_kern_ctx)
@@ -12862,6 +12864,7 @@ static bool is_bpf_list_api_kfunc(u32 btf_id)
 	       btf_id == special_kfunc_list[KF_bpf_list_push_back_impl] ||
 	       btf_id == special_kfunc_list[KF_bpf_list_pop_front] ||
 	       btf_id == special_kfunc_list[KF_bpf_list_pop_back] ||
+	       btf_id == special_kfunc_list[KF_bpf_list_del] ||
 	       btf_id == special_kfunc_list[KF_bpf_list_front] ||
 	       btf_id == special_kfunc_list[KF_bpf_list_back];
 }
@@ -12970,7 +12973,8 @@ static bool check_kfunc_is_graph_node_api(struct bpf_verifier_env *env,
 	switch (node_field_type) {
 	case BPF_LIST_NODE:
 		ret = (kfunc_btf_id == special_kfunc_list[KF_bpf_list_push_front_impl] ||
-		       kfunc_btf_id == special_kfunc_list[KF_bpf_list_push_back_impl]);
+		       kfunc_btf_id == special_kfunc_list[KF_bpf_list_push_back_impl] ||
+		       kfunc_btf_id == special_kfunc_list[KF_bpf_list_del]);
 		break;
 	case BPF_RB_NODE:
 		ret = (kfunc_btf_id == special_kfunc_list[KF_bpf_rbtree_remove] ||
-- 
2.50.1 (Apple Git-155)

Re: [PATCH 1/2] bpf: Introduce the bpf_list_del kfunc.

[Alexei Starovoitov]

On Sun, Feb 8, 2026 at 6:53 PM Chengkaitao <pilgrimtao@gmail.com> wrote:
>
> From: Kaitao Cheng <chengkaitao@kylinos.cn>
>
> If a user holds ownership of a node in the middle of a list, they
> can directly remove it from the list without strictly adhering to
> deletion rules from the head or tail.
>
> This is typically paired with bpf_refcount. After calling
> bpf_list_del, it is generally necessary to drop the reference to
> the list node twice to prevent reference count leaks.
>
> Signed-off-by: Kaitao Cheng <chengkaitao@kylinos.cn>
> ---
>  kernel/bpf/helpers.c  | 19 +++++++++++++++++++
>  kernel/bpf/verifier.c |  6 +++++-
>  2 files changed, 24 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index db72b96f9c8c..44d9b9ea8d40 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -2388,6 +2388,24 @@ __bpf_kfunc struct bpf_list_node *bpf_list_pop_back(struct bpf_list_head *head)
>         return __bpf_list_del(head, true);
>  }
>
> +__bpf_kfunc struct bpf_list_node *bpf_list_del(struct bpf_list_head *head,
> +                                              struct bpf_list_node *node)
> +{
> +       struct bpf_list_node_kern *knode = (struct bpf_list_node_kern *)node;
> +       struct list_head *h = (void *)head;
> +
> +       if (unlikely(!knode))
> +               return NULL;
> +
> +       if (WARN_ON_ONCE(READ_ONCE(knode->owner) != h))
> +               return NULL;

Existing __bpf_list_del() is actually using 'head',
but here... passing 'head' just to warn on it ?
Seems overkill.
Pass 'node' only. Then it will be more list-like.

Any other apis are missing?

pw-bot: cr

[PATCH 2/2] selftests/bpf: Add test cases for bpf_list_del

[Chengkaitao]

From: Kaitao Cheng <chengkaitao@kylinos.cn>

Add a node to both an rbtree and a list, retrieve the node from
the rbtree, use the obtained node pointer to remove it from the
list, and finally free the node.

Signed-off-by: Kaitao Cheng <chengkaitao@kylinos.cn>
---
 .../testing/selftests/bpf/bpf_experimental.h  | 11 +++++
 .../selftests/bpf/progs/refcounted_kptr.c     | 41 +++++++++++++++++++
 2 files changed, 52 insertions(+)

diff --git a/tools/testing/selftests/bpf/bpf_experimental.h b/tools/testing/selftests/bpf/bpf_experimental.h
index 2cd9165c7348..6d8175abc590 100644
--- a/tools/testing/selftests/bpf/bpf_experimental.h
+++ b/tools/testing/selftests/bpf/bpf_experimental.h
@@ -99,6 +99,17 @@ 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
  *	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..2cb6dd73db7a 100644
--- a/tools/testing/selftests/bpf/progs/refcounted_kptr.c
+++ b/tools/testing/selftests/bpf/progs/refcounted_kptr.c
@@ -367,6 +367,47 @@ 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 node_data into both rbtree and list, remove from tree, then remove
+ * from list via bpf_list_del using the node obtained from the tree.
+ */
+SEC("tc")
+__description("test_bpf_list_del: remove an arbitrary node from the list")
+__success __retval(0)
+long test_bpf_list_del(void *ctx)
+{
+	long err;
+	struct bpf_rb_node *rb;
+	struct bpf_list_node *l;
+	struct node_data *n;
+
+	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);
+
+	bpf_spin_lock(&lock);
+	l = bpf_list_del(&head, &n->l);
+	bpf_spin_unlock(&lock);
+	bpf_obj_drop(n);
+	if (!l)
+		return -6;
+
+	bpf_obj_drop(container_of(l, struct node_data, l));
+	return 0;
+}
+
 SEC("tc")
 __success
 long rbtree_refcounted_node_ref_escapes(void *ctx)
-- 
2.50.1 (Apple Git-155)