I have clarified this issue in the [PATCH bpf-next v10 1/8] patch, with the link provided below:
https://lore.kernel.org/bpf/[email protected]/ 在 2026/5/12 14:41, [email protected] 写道: >> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c >> index baa12b24bb64..9cd7b028592c 100644 >> --- a/kernel/bpf/helpers.c >> +++ b/kernel/bpf/helpers.c >> @@ -2550,22 +2550,24 @@ __bpf_kfunc int bpf_list_push_back_impl(struct >> bpf_list_head *head, >> return bpf_list_push_back(head, node, meta__ign, off); >> } >> >> -static struct bpf_list_node *__bpf_list_del(struct bpf_list_head *head, >> bool tail) >> +static struct bpf_list_node *__bpf_list_del(struct bpf_list_head *head, >> + struct list_head *n) >> { >> - struct list_head *n, *h = (void *)head; >> + struct list_head *h = (void *)head; >> struct bpf_list_node_kern *node; >> >> /* If list_head was 0-initialized by map, bpf_obj_init_field wasn't >> * called on its fields, so init here >> */ >> - if (unlikely(!h->next)) >> + if (unlikely(!h->next)) { >> INIT_LIST_HEAD(h); >> + return NULL; >> + } >> if (list_empty(h)) >> return NULL; >> >> - n = tail ? h->prev : h->next; >> node = container_of(n, struct bpf_list_node_kern, list_head); >> - if (WARN_ON_ONCE(READ_ONCE(node->owner) != head)) >> + if (unlikely(READ_ONCE(node->owner) != head)) >> return NULL; >> >> list_del_init(n); >> @@ -2575,12 +2577,16 @@ static struct bpf_list_node *__bpf_list_del(struct >> bpf_list_head *head, bool tai >> >> __bpf_kfunc struct bpf_list_node *bpf_list_pop_front(struct bpf_list_head >> *head) >> { >> - return __bpf_list_del(head, false); >> + struct list_head *h = (void *)head; >> + >> + return __bpf_list_del(head, h->next); >> } > > The new code reads h->next before __bpf_list_del checks if the list is > initialized. If the list is uninitialized (h->next is NULL), a NULL pointer > is passed to __bpf_list_del. > > While __bpf_list_del eventually initializes the list and returns NULL without > dereferencing the NULL pointer, this is counterintuitive - passing a > potentially garbage value that is later ignored. > > Can you move the initialization check into the top-level kfuncs > (bpf_list_pop_front and bpf_list_pop_back) to ensure the list_head passed to > __bpf_list_del is always valid? You could initialize the list and return NULL > in that case - we know it's empty. > > This concern was raised by Emil Tsalapatis in v8: > https://lore.kernel.org/bpf/[email protected]/ > >> >> __bpf_kfunc struct bpf_list_node *bpf_list_pop_back(struct bpf_list_head >> *head) >> { >> - return __bpf_list_del(head, true); >> + struct list_head *h = (void *)head; >> + >> + return __bpf_list_del(head, h->prev); >> } > > > --- > 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/25716874656 -- Thanks Kaitao Cheng
