linux-kernel - Re: [PATCH bpf-next v12 2/7] bpf: Add BPF_F_CPU and BPF_F_ALL_CPUS flags support for percpu

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Message-ID: <68ecc660-1e02-4aa6-9bf1-3e56c3a23da4@linux.dev>
Date: Wed, 26 Nov 2025 14:20:06 -0800
From: Ihor Solodrai <ihor.solodrai@...ux.dev>
To: Chris Mason <clm@...a.com>, Leon Hwang <leon.hwang@...ux.dev>,
 bot+bpf-ci@...nel.org, bpf@...r.kernel.org
Cc: ast@...nel.org, andrii@...nel.org, daniel@...earbox.net,
 jolsa@...nel.org, yonghong.song@...ux.dev, song@...nel.org,
 eddyz87@...il.com, dxu@...uu.xyz, deso@...teo.net, martin.lau@...ux.dev,
 john.fastabend@...il.com, kpsingh@...nel.org, sdf@...ichev.me,
 haoluo@...gle.com, shuah@...nel.org, kerneljasonxing@...il.com,
 chen.dylane@...ux.dev, willemb@...gle.com, paul.chaignon@...il.com,
 a.s.protopopov@...il.com, memxor@...il.com, yatsenko@...a.com,
 tklauser@...tanz.ch, kernel-patches-bot@...com,
 linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
 martin.lau@...nel.org
Subject: Re: [PATCH bpf-next v12 2/7] bpf: Add BPF_F_CPU and BPF_F_ALL_CPUS
 flags support for percpu_array maps

On 11/26/25 7:56 AM, Chris Mason wrote:
> 
> 
> On 11/26/25 10:24 AM, Leon Hwang wrote:
>>
>>
>> On 2025/11/26 23:11, bot+bpf-ci@...nel.org wrote:
>>>> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
>>>> index d84af3719..01a99e3a3 100644
>>>> --- a/include/linux/bpf.h
>>>> +++ b/include/linux/bpf.h
>>>
>>> [ ... ]
>>>
>>>> diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
>>>> index 1eeb31c5b..67e9e811d 100644
>>>> --- a/kernel/bpf/arraymap.c
>>>> +++ b/kernel/bpf/arraymap.c
>>>
>>> [ ... ]
>>>
>>>> @@ -398,10 +405,11 @@ int bpf_percpu_array_update(struct bpf_map *map, void *key, void *value,
>>>>  	struct bpf_array *array = container_of(map, struct bpf_array, map);
>>>>  	u32 index = *(u32 *)key;
>>>>  	void __percpu *pptr;
>>>> -	int cpu, off = 0;
>>>> +	void *ptr, *val;
>>>>  	u32 size;
>>>> +	int cpu;
>>>>
>>>> -	if (unlikely(map_flags > BPF_EXIST))
>>>> +	if (unlikely((map_flags & BPF_F_LOCK) || (u32)map_flags > BPF_F_ALL_CPUS))
>>>>  		/* unknown flags */
>>>>  		return -EINVAL;
>>>>
>>>> @@ -409,7 +417,7 @@ int bpf_percpu_array_update(struct bpf_map *map, void *key, void *value,
>>>>  		/* all elements were pre-allocated, cannot insert a new one */
>>>>  		return -E2BIG;
>>>>
>>>> -	if (unlikely(map_flags & BPF_NOEXIST))
>>>> +	if (unlikely(map_flags == BPF_NOEXIST))
>>>                               ^^
>>>
>>
>> ?
>>
>> No such change in this version.
>>
>> It seems that this change was inferred from v11 to v12 by AI itself
> 
> Thanks for flagging this, I'll try to find this section of the logs to
> see how the false positive checks failed to catch it.
> 
> -chris

AI got confused here, this was not in the diff.

But it appears it got triggered, because there are these two code
fragments nearby [1]:


	if (unlikely(map_flags & BPF_NOEXIST))
		/* all elements already exist */
		return -EEXIST;

and

	if (unlikely(map_flags == BPF_NOEXIST))
		/* all elements already exist */
		return -EEXIST;

Which is a good thing to notice even if this is intentional.

Anyone knows if it is?

https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/kernel/bpf/arraymap.c#n356

>