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 <redacted>