linux-kernel - Re: [PATCH bpf-next 1/4] bpf: enable task local storage for tracing programs

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Date:   Mon, 11 Jan 2021 23:16:48 +0000
From:   Song Liu <songliubraving@...com>
To:     KP Singh <kpsingh@...nel.org>
CC:     bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        "Peter Zijlstra" <peterz@...radead.org>,
        Alexei Starovoitov <ast@...nel.org>,
        "Daniel Borkmann" <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        "John Fastabend" <john.fastabend@...il.com>,
        Kernel Team <Kernel-team@...com>,
        "Hao Luo" <haoluo@...gle.com>, kernel test robot <lkp@...el.com>
Subject: Re: [PATCH bpf-next 1/4] bpf: enable task local storage for tracing
 programs



> On Jan 11, 2021, at 2:14 AM, KP Singh <kpsingh@...nel.org> wrote:
> 
> On Sat, Jan 9, 2021 at 12:35 AM Song Liu <songliubraving@...com> wrote:
>> 
>> To access per-task data, BPF program typically creates a hash table with
>> pid as the key. This is not ideal because:
>> 1. The use need to estimate requires size of the hash table, with may be
>>    inaccurate;
>> 2. Big hash tables are slow;
>> 3. To clean up the data properly during task terminations, the user need
>>    to write code.
>> 
>> Task local storage overcomes these issues and becomes a better option for
>> these per-task data. Task local storage is only available to BPF_LSM. Now
>> enable it for tracing programs.
> 
> Also mention here that you change the pointer from being a security blob to a
> dedicated member in the task struct. I assume this is because you want to
> use it without CONFIG_BPF_LSM?

Yes, exactly. I will add this to the commit log. 

> 
>> 
> 
> Can you also mention the reasons for changing the
> raw_spin_lock_bh to raw_spin_lock_irqsave in the commit log?

This is because we will use these in irq context. I will add this to the 
commit log. 

Thanks,
Song