Re: [PATCH v3] kernel/bpf/btf.c: reject to register duplicated kfunc

[Song Chen <chensong_2000@126.com>]

Hi,

在 2026/6/2 00:09, Yonghong Song 写道:
> 
> 
> On 6/1/26 2:39 AM, Song Chen wrote:
>> Hi Kaitao,
>>
>> 在 2026/5/25 17:18, Kaitao Cheng 写道:
>>> 在 2026/5/24 16:29, Song Chen 写道:
>>>> I had an ebpf program which calls a kfunc defined and
>>>> implemented in one of my kernel modules, it was working
>>>> fine in 6.16, but was rejected to run by libbpf in 6.19,
>>>> the error message was:
>>>>
>>>> libbpf: extern (func ksym) 'bpf_strstr': func_proto [5]
>>>> incompatible with vmlinux [94389]
>>>>
>>>> The reason is there is a new added kfunc in kernel 6.19
>>>> which happens to be the same name with my kfunc. However the
>>>> error message is not obvious enough to address problem
>>>> immediately.
>>>>
>>>> Therefore, this patches searches duplicated kfunc in
>>>> both btf_vmlinux and btf_modules list before a kernel module
>>>> attempts to register kfuncs through register_btf_kfunc_id_set,
>>>> it prints clear error message and returns error code if same name
>>>> kfunc has already implemented and registered, then developer
>>>> knows at the first place.
>>>>
>>>> Suggested-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
>>>> Suggested-by: Kaitao Cheng <kaitao.cheng@linux.dev>
>>>> Signed-off-by: Song Chen <chensong_2000@126.com>
>>>>
>>>> ---
>>>> changelog:
>>>> v1 --- v2:
>>>> libbpf has already specified which module this kfunc belongs to as
>>>> ebpf code onwer's expectation, then verifier uses
>>>> find_kallsyms_symbol_value to search kfunc's addr.
>>>>
>>>> v2 --- v3:
>>>> After v2, I tried a new idea of introducing a namespace in libbpf
>>>> to specify kfunc owner in an ebpf program suggested by Kaitao Cheng,
>>>> please see [1]. Alex suggested to go back to report an error during
>>>> kmod load on conflicting kfunc name for now. What's more, v2 only
>>>> searched bpf_vmlinux, v3 also traverses btf_modules list.
>>>>
>>>> [1]:https://lore.kernel.org/all/ 
>>>> CAADnVQ+jYGMjAC9aNygmhyppUO9foWN4z9cjSpwCEXAFHpRVJQ@mail.gmail.com/
>>>> ---
>>>>   kernel/bpf/btf.c | 44 +++++++++++++++++++++++++++++++++++++++++++-
>>>>   1 file changed, 43 insertions(+), 1 deletion(-)
>>>>
>>>
>>> btf: reject to register duplicated kfunc
>>>> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
>>>> index 4872d2a6c42d..a14ad3720872 100644
>>>> --- a/kernel/bpf/btf.c
>>>> +++ b/kernel/bpf/btf.c
>>>> @@ -8618,6 +8618,47 @@ static int btf_check_iter_kfuncs(struct btf 
>>>> *btf, const char *func_name,
>>>>       return 0;
>>>>   }
>>>>   +static int btf_check_kfunc_name(struct btf *btf, const char 
>>>> *func_name, u32 kind)
>>>> +{
>>>> +#ifdef CONFIG_DEBUG_INFO_BTF_MODULES
>>>> +    struct btf_module *btf_mod, *tmp;
>>>> +#endif
>>>> +    s32 id;
>>>> +    int ret = 0;
>>>
>>> This ret variable may be unnecessary.
>>>
>>>> +
>>>> +    if (!btf_is_module(btf))
>>>> +        goto out;
>>>> +
>>>> +    id = btf_find_by_name_kind(bpf_get_btf_vmlinux(),
>>>> +                    func_name, kind);
>>>
>>> It seems unnecessary to split this call across multiple lines. Also,
>>> some of the continuation-line indentation elsewhere does not appear
>>> to follow the kernel coding style.
>>>
>>>> +    if (id >= 0) {
>>>> +        pr_err("kfunc %s (id: %d) is already present in vmlinux.\n",
>>>> +                    func_name, id);
>>>> +        ret = -EINVAL;
>>>> +        goto out;
>>>
>>> return -EINVAL;
>>>
>>>> +    }
>>>> +
>>>> +#ifdef CONFIG_DEBUG_INFO_BTF_MODULES
>>>> +    mutex_lock(&btf_module_mutex);
>>>> +    list_for_each_entry_safe(btf_mod, tmp, &btf_modules, list) {
>>>> +        if (btf_mod->btf == btf)
>>>> +            continue;
>>>> +        id = btf_find_by_name_kind(btf_mod->btf,
>>>> +                    func_name, kind);
>>>> +        if (id >= 0) {
>>>> +            pr_err("kfunc %s (id: %d) is already present in module 
>>>> %s.\n",
>>>> +                    func_name, id, btf_mod->module->name);
>>>
>>> follow the kernel coding style
>>
>> I understood the rest part of your comments, but this one "follow the 
>> kernel coding style", is it an indentation problem? checkpatch didn't 
>> say anything about it.
> 
> See Documentation/process/coding-style.rst.
> 
> [...]
> 

helpful, thanks.

/Song