linux-kernel - Re: [PATCH bpf-next v6 1/2] bpf: refactor max_depth computation in bpf_get

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Message-ID: <d6223a4c-3e24-464f-893b-6bef57b973b8@arnaud-lcm.com>
Date: Wed, 3 Sep 2025 18:20:43 +0200
From: "Lecomte, Arnaud" <contact@...aud-lcm.com>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Yonghong Song <yonghong.song@...ux.dev>, Song Liu <song@...nel.org>,
 Andrii Nakryiko <andrii@...nel.org>, Alexei Starovoitov <ast@...nel.org>,
 bpf <bpf@...r.kernel.org>, Daniel Borkmann <daniel@...earbox.net>,
 Eduard <eddyz87@...il.com>, Hao Luo <haoluo@...gle.com>,
 John Fastabend <john.fastabend@...il.com>, Jiri Olsa <jolsa@...nel.org>,
 KP Singh <kpsingh@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
 Martin KaFai Lau <martin.lau@...ux.dev>, Stanislav Fomichev
 <sdf@...ichev.me>, syzbot+c9b724fbb41cf2538b7b@...kaller.appspotmail.com,
 syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: [PATCH bpf-next v6 1/2] bpf: refactor max_depth computation in
 bpf_get_stack()


On 03/09/2025 18:12, Alexei Starovoitov wrote:
> On Wed, Sep 3, 2025 at 6:52 AM Arnaud Lecomte <contact@...aud-lcm.com> wrote:
>> A new helper function stack_map_calculate_max_depth() that
>> computes the max depth for a stackmap.
>>
>> Changes in v2:
>>   - Removed the checking 'map_size % map_elem_size' from
>>     stack_map_calculate_max_depth
>>   - Changed stack_map_calculate_max_depth params name to be more generic
>>
>> Changes in v3:
>>   - Changed map size param to size in max depth helper
>>
>> Changes in v4:
>>   - Fixed indentation in max depth helper for args
>>
>> Changes in v5:
>>   - Bound back trace_nr to num_elem in __bpf_get_stack
>>   - Make a copy of sysctl_perf_event_max_stack
>>     in stack_map_calculate_max_depth
>>
>> Changes in v6:
>>   - Restrained max_depth computation only when required
>>   - Additional cleanup from Song in __bpf_get_stack
> This is not a refactor anymore.
> Pls don't squash different things into one patch.
> Keep refactor as patch 1, and another cleanup as patch 2.

The main problem is that patch 2 is not a cleanup too. It is a bug fix 
so it doesn't really
fit either.
We could maybe split this patch into 2 new patches but I don't really 
like this idea.
If we decide to stick to 2 patches format, I don't have any preference 
which patch's scope
should be extended.

>
> pw-bot: cr
>