linux-kernel - Re: [PATCH v5 bpf-next 1/6] bpf: enable task local storage for tracing programs

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Date:   Tue, 23 Feb 2021 17:00:36 -0800
From:   Yonghong Song <yhs@...com>
To:     Song Liu <songliubraving@...com>, <bpf@...r.kernel.org>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC:     <ast@...nel.org>, <daniel@...earbox.net>, <kernel-team@...com>,
        <peterz@...radead.org>, kernel test robot <lkp@...el.com>,
        KP Singh <kpsingh@...nel.org>
Subject: Re: [PATCH v5 bpf-next 1/6] bpf: enable task local storage for
 tracing programs



On 2/23/21 2:28 PM, Song Liu wrote:
> To access per-task data, BPF programs usually creates a hash table with
> pid as the key. This is not ideal because:
>   1. The user need to estimate the proper size of the hash table, which may
>      be inaccurate;
>   2. Big hash tables are slow;
>   3. To clean up the data properly during task terminations, the user need
>      to write extra logic.
> 
> Task local storage overcomes these issues and offers a better option for
> these per-task data. Task local storage is only available to BPF_LSM. Now
> enable it for tracing programs.
> 
> Unlike LSM programs, tracing programs can be called in IRQ contexts.
> Helpers that access task local storage are updated to use
> raw_spin_lock_irqsave() instead of raw_spin_lock_bh().
> 
> Tracing programs can attach to functions on the task free path, e.g.
> exit_creds(). To avoid allocating task local storage after
> bpf_task_storage_free(). bpf_task_storage_get() is updated to not allocate
> new storage when the task is not refcounted (task->usage == 0).
> 
> Reported-by: kernel test robot <lkp@...el.com>

For a patch like this, typically we do not put the above
Reported-by here as it is not really reported by the
kernel test robot. If no revision is required, maybe
maintainer can remove it before applying.

> Acked-by: KP Singh <kpsingh@...nel.org>
> Signed-off-by: Song Liu <songliubraving@...com>
> ---
>   include/linux/bpf.h            |  7 ++++++
>   include/linux/bpf_lsm.h        | 22 -----------------
>   include/linux/bpf_types.h      |  2 +-
>   include/linux/sched.h          |  5 ++++
>   kernel/bpf/Makefile            |  3 +--
>   kernel/bpf/bpf_local_storage.c | 28 +++++++++++++---------
>   kernel/bpf/bpf_lsm.c           |  4 ----
>   kernel/bpf/bpf_task_storage.c  | 43 +++++++++-------------------------
>   kernel/fork.c                  |  5 ++++
>   kernel/trace/bpf_trace.c       |  4 ++++
>   10 files changed, 51 insertions(+), 72 deletions(-)
> 
[...]