[PATCH bpf-next v3 0/7] bpf: Introduce deferred task context execution

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

From: Mykyta Yatsenko <yatsenko@meta.com>

This patch introduces a new mechanism for BPF programs to schedule
deferred execution in the context of a specific task using the kernel’s
task_work infrastructure.

The new bpf_task_work interface enables BPF use cases that
require sleepable subprogram execution within task context, for example,
scheduling sleepable function from the context that does not
allow sleepable, such as NMI.

Introduced kfuncs bpf_task_work_schedule_signal() and
bpf_task_work_schedule_resume() for scheduling BPF callbacks correspond
to different modes used by task_work (TWA_SIGNAL or TWA_RESUME).

The implementation manages scheduling state via metadata objects (struct
bpf_task_work_context). Pointers to bpf_task_work_context are stored
in BPF map values. State transitions are handled via an atomic
state machine (bpf_task_work_state) to ensure correctness under
concurrent usage and deletion, lifetime is guarded by refcounting and
RCU Tasks Trace.
Kfuncs call task_work_add() indirectly via irq_work to avoid locking in
potentially NMI context.

v2 -> v3
 * Introduce ref counting
 * Add patches with minor verifier and btf.c refactorings to avoid code
duplication
 * Rework initiation of the task work scheduling to handle race with map
usercnt dropping to zero

Mykyta Yatsenko (7):
  bpf: refactor special field-type detection
  bpf: extract generic helper from process_timer_func()
  bpf: htab: extract helper for freeing special structs
  bpf: bpf task work plumbing
  bpf: extract map key pointer calculation
  bpf: task work scheduling kfuncs
  selftests/bpf: BPF task work scheduling tests

 include/linux/bpf.h                           |  11 +
 include/uapi/linux/bpf.h                      |   4 +
 kernel/bpf/arraymap.c                         |   8 +-
 kernel/bpf/btf.c                              |  63 ++-
 kernel/bpf/hashtab.c                          |  43 +-
 kernel/bpf/helpers.c                          | 386 +++++++++++++++++-
 kernel/bpf/syscall.c                          |  16 +-
 kernel/bpf/verifier.c                         | 136 +++++-
 tools/include/uapi/linux/bpf.h                |   4 +
 .../selftests/bpf/prog_tests/test_task_work.c | 149 +++++++
 tools/testing/selftests/bpf/progs/task_work.c | 108 +++++
 .../selftests/bpf/progs/task_work_fail.c      |  98 +++++
 12 files changed, 932 insertions(+), 94 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/test_task_work.c
 create mode 100644 tools/testing/selftests/bpf/progs/task_work.c
 create mode 100644 tools/testing/selftests/bpf/progs/task_work_fail.c

-- 
2.51.0