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

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Message-ID: <1797f2fd-2b34-4c6b-bc61-043e01fde417@linux.dev>
Date: Thu, 7 Aug 2025 12:07:15 -0700
From: Yonghong Song <yonghong.song@...ux.dev>
To: Arnaud Lecomte <contact@...aud-lcm.com>
Cc: andrii@...nel.org, ast@...nel.org, bpf@...r.kernel.org,
 daniel@...earbox.net, eddyz87@...il.com, haoluo@...gle.com,
 john.fastabend@...il.com, jolsa@...nel.org, kpsingh@...nel.org,
 linux-kernel@...r.kernel.org, martin.lau@...ux.dev, sdf@...ichev.me,
 song@...nel.org, syzbot+c9b724fbb41cf2538b7b@...kaller.appspotmail.com,
 syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH 1/2] bpf: refactor max_depth computation in
 bpf_get_stack()



On 8/7/25 12:01 PM, Yonghong Song wrote:
>
>
> On 8/7/25 10:50 AM, Arnaud Lecomte wrote:
>> A new helper function stack_map_calculate_max_depth() that
>> computes the max depth for a stackmap.
>>
>> Signed-off-by: Arnaud Lecomte <contact@...aud-lcm.com>
>> ---
>>   kernel/bpf/stackmap.c | 38 ++++++++++++++++++++++++++++++--------
>>   1 file changed, 30 insertions(+), 8 deletions(-)
>>
>> diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
>> index 3615c06b7dfa..14e034045310 100644
>> --- a/kernel/bpf/stackmap.c
>> +++ b/kernel/bpf/stackmap.c
>> @@ -42,6 +42,31 @@ static inline int stack_map_data_size(struct 
>> bpf_map *map)
>>           sizeof(struct bpf_stack_build_id) : sizeof(u64);
>>   }
>>   +/**
>> + * stack_map_calculate_max_depth - Calculate maximum allowed stack 
>> trace depth
>> + * @map_size:        Size of the buffer/map value in bytes
>> + * @elem_size:       Size of each stack trace element
>> + * @map_flags:       BPF stack trace flags (BPF_F_USER_STACK, 
>> BPF_F_USER_BUILD_ID, ...)

One more thing: map_flags -> flags, as 'flags is used in bpf_get_stackid/bpf_get_stack etc.

>> + *
>> + * Return: Maximum number of stack trace entries that can be safely 
>> stored,
>> + * or -EINVAL if size is not a multiple of elem_size
>
> -EINVAL is not needed here. See below.

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