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

[Yonghong Song]

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@xxxxxxxxx>

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@xxxxxxxxxx>
> Signed-off-by: Song Liu <songliubraving@xxxxxx>
> ---
>   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(-)
[...]