[PATCH RFC v2 0/5] bpf: avoid locks in bpf_timer and bpf_wq

[Mykyta Yatsenko <mykyta.yatsenko5@gmail.com>]

This series reworks implementation of BPF timer and workqueue APIs.
The goal is to make both timers and wq non-blocking, enabling their use
in NMI context.
Today this code relies on a bpf_spin_lock embedded in the map element to
serialize:
 * init of the async object,
 * setting/changing the callback and bpf_prog
 * starting/cancelling the timer/work
 * tearing down when the map element is deleted or the map’s user ref is
 dropped

The series apply design similar to existing bpf_task_work
approach [1]: RCU and refcount to maintain lifetime guarantees and state
machine to handle data races.

This RFC doesn’t yet fully add NMI support for timers
and workqueue helpers and kfuncs, but it takes the first step by
removing the spinlock from bpf_async_cb struct.

---
1: https://lore.kernel.org/bpf/175864081800.1466288.3242104888617580131.git-patchwork-notify@kernel.org/

Signed-off-by: Mykyta Yatsenko <yatsenko@meta.com>

---
Changes in v2:
- Move refcnt initialization and put (from cancel_and_free())
from patch 5 into the patch 4, so that patch 4 has more clear and full
implementation and use of refcnt
- Link to v1: https://lore.kernel.org/r/20251031-timer_nolock-v1-0-b064ae403bfb@meta.com

---
Mykyta Yatsenko (5):
      bpf: refactor bpf_async_cb callback update
      bpf: refactor bpf_async_cb prog swap
      bpf: factor out timer deletion helper
      bpf: add refcnt into struct bpf_async_cb
      bpf: remove lock from bpf_async_cb

 kernel/bpf/helpers.c | 309 +++++++++++++++++++++++++++++++--------------------
 1 file changed, 189 insertions(+), 120 deletions(-)
---
base-commit: 23f852daa4bab4d579110e034e4d513f7d490846
change-id: 20251028-timer_nolock-457f5b9daace

Best regards,
-- 
Mykyta Yatsenko <yatsenko@meta.com>