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

[Martin KaFai Lau]

On Tue, Feb 23, 2021 at 02:28:40PM -0800, 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).
Acked-by: Martin KaFai Lau <kafai@xxxxxx>