[RFC PATCH v2 0/9] rv: Verify generic IRQ context transitions

[Karl Mehltretter <kmehltretter@gmail.com>]

IRQ action tracepoints describe handlers, but not the lifetime of the
enclosing IRQ context. One context may run several actions, and an action
may be dispatched outside hardirq context. PREEMPT_RT may also enter
serving-softirq state without invoking an action. This leaves no generic
event stream from which an RV monitor can check IRQ-context transitions.

This RFC adds tracepoints at the generic hardirq and serving-softirq
boundaries. The irq:irqstate RV monitor checks their order and agreement
with live kernel state. irq:irqexit follows the owner of a
preempt_schedule_irq() invocation across task switches and CPU migration.

The hardirq tracepoints cover paths through irq_enter() or
irq_enter_rcu() and their matching exits. They do not cover direct
__irq_enter() and __irq_exit() users, raw paths, or architecture-specific
entry and return intervals. irqexit covers preempt_schedule_irq(), not
the complete interrupt-return path.

Boundary callbacks can raise softirq work after the pending-work check.
The series wakes ksoftirqd or ktimerd for remaining work. KUnit covers
nesting, monitor synchronization, PREEMPT_RT worker intervals, provenance
and late-work handoff.

Gabriele answered two of the v1 questions [1]:

  - The boundaries are now bare DECLARE_TRACE() tracepoints like the
    existing RV hooks in include/trace/events/sched.h, so they add no
    tracefs ABI.
  - irqstate and irqexit stay separate automata because one is per-CPU
    and the other per-task. A hardirq or non-RT softirq belongs to the
    CPU it interrupts. A preempt_schedule_irq() invocation belongs to
    the interrupted task, several tasks can be inside one at the same
    time, and it can migrate before it returns. Each RV automaton has a
    single monitor type. Both now sit under an irq container, so they
    are enabled together by default, and the irqentry/irqexit naming
    clash is gone.

Questions still open from v1:

  1. Are dedicated scheduler tracepoints the right way to follow
     preempt_schedule_irq() across task switches and migration?
  2. Is the KUnit-only hook for an empty ksoftirqd invocation
     acceptable? Outside a KUnit run, its worker checks take a disabled
     static-key path.

Patches 1-5 add the tracepoints, monitors and documentation. Patches 6-9
add KUnit coverage.

The series is based on v7.4-rc1, which contains the v1 prerequisite and
Wen Yang's reactor lockdep fix:

  commit feb5c9a2447a ("softirq: Preserve interrupt context on return from interrupt")
  commit 39ccedfd9e55 ("rv: Use LD_WAIT_SPIN as the reactor lockdep wait type")

The series is independent of the early-hardirq series [2], which
installs hardirq state before entry tracing. Both change
kernel/softirq.c, so applying one on top of the other needs a small
conflict resolution in __irq_exit_rcu().

Changes since v1:

  - Use bare DECLARE_TRACE() tracepoints instead of trace events
    (Gabriele)
  - Rename the irqentry container to irq (Gabriele)
  - Add text schematics of both models to the documentation (Gabriele)
  - Document why irqstate and irqexit are separate automata
  - Rebase onto v7.4-rc1

Testing on v7.4-rc1 with Clang 23.1.5, GCC 14.2 (x86) and GCC 16.2
(cross), and QEMU 10.0 TCG, with lockdep and the locking selftests:

  - Each patch builds with W=1 on x86_64 without new warnings.
    RV_MONITORS_KUNIT_TEST=m builds on x86_64 and arm64. kernel-doc
    reports no warnings for the changed headers.
  - The rv_mon KUnit suite and the reactor suites passed without
    failures on:

      x86_64   PREEMPT SMP4 and UP, PREEMPT with nohz_full=1-3 and
               threadirqs, PREEMPT_RT SMP4, PREEMPT_RT SMP8 with
               nohz_full=1-3
      arm64    PREEMPT, PREEMPT with nohz_full=1-3 and threadirqs,
               PREEMPT_RT, PREEMPT_RT SMP8 with nohz_full=1-3
      riscv64  PREEMPT
      ARMv7    UP

    Each configuration ran 13 to 21 of the 29 rv_mon cases. The others
    are skipped because they need a different configuration.
  - RV=n kernels boot on x86_64 and arm64.
  - On top of the early-hardirq series, the same suites passed on
    x86_64 (PREEMPT, PREEMPT_RT), arm64 (PREEMPT, PREEMPT_RT) and
    riscv64.

An LLM assisted with the patches and the testing.

v1: https://lore.kernel.org/all/20261022050712.75035-1-kmehltretter@gmail.com/

[1] https://lore.kernel.org/all/FACA54EC-F846-4051-9ADD-DB46E7665FAD@redhat.com/
[2] https://lore.kernel.org/all/20261028033127.82193-1-kmehltretter@gmail.com/

Karl Mehltretter (9):
  tracing/irq: Add generic IRQ context boundary tracepoints
  tracing/sched: Add IRQ preemption lifecycle tracepoints
  rv: Add a monitor for generic IRQ context transitions
  rv: Add a monitor for IRQ-exit scheduling ownership
  docs/rv: Document the IRQ monitors
  rv: Add KUnit coverage for IRQ context transitions
  rv: Add KUnit coverage for IRQ-exit scheduling
  rv: Test empty PREEMPT_RT softirq worker intervals
  rv: Test IRQ-exit softirq provenance and handoff

 Documentation/trace/rv/index.rst              |    1 +
 Documentation/trace/rv/monitor_irq.rst        |  475 ++++
 include/linux/interrupt.h                     |    8 +
 include/rv/kunit.h                            |   34 +-
 include/trace/events/irq.h                    |   56 +
 include/trace/events/sched.h                  |   26 +
 kernel/sched/core.c                           |    6 +
 kernel/softirq.c                              |  324 ++-
 kernel/trace/rv/Kconfig                       |   11 +-
 kernel/trace/rv/Makefile                      |    3 +
 kernel/trace/rv/monitors/irq/Kconfig          |   13 +
 kernel/trace/rv/monitors/irq/irq.c            |   35 +
 kernel/trace/rv/monitors/irq/irq.h            |    3 +
 kernel/trace/rv/monitors/irqexit/Kconfig      |   14 +
 kernel/trace/rv/monitors/irqexit/irqexit.c    |  172 ++
 kernel/trace/rv/monitors/irqexit/irqexit.h    |   85 +
 .../trace/rv/monitors/irqexit/irqexit_kunit.c |  540 ++++
 .../trace/rv/monitors/irqexit/irqexit_kunit.h |   21 +
 .../trace/rv/monitors/irqexit/irqexit_trace.h |   19 +
 kernel/trace/rv/monitors/irqstate/Kconfig     |   14 +
 kernel/trace/rv/monitors/irqstate/irqstate.c  |  289 ++
 kernel/trace/rv/monitors/irqstate/irqstate.h  |  139 +
 .../rv/monitors/irqstate/irqstate_kunit.c     | 2339 +++++++++++++++++
 .../rv/monitors/irqstate/irqstate_kunit.h     |   25 +
 .../rv/monitors/irqstate/irqstate_trace.h     |   15 +
 kernel/trace/rv/rv_monitors_test.c            |   30 +
 kernel/trace/rv/rv_trace.h                    |    2 +
 tools/verification/models/irq/irqexit.dot     |   21 +
 tools/verification/models/irq/irqstate.dot    |   32 +
 29 files changed, 4737 insertions(+), 15 deletions(-)
 create mode 100644 Documentation/trace/rv/monitor_irq.rst
 create mode 100644 kernel/trace/rv/monitors/irq/Kconfig
 create mode 100644 kernel/trace/rv/monitors/irq/irq.c
 create mode 100644 kernel/trace/rv/monitors/irq/irq.h
 create mode 100644 kernel/trace/rv/monitors/irqexit/Kconfig
 create mode 100644 kernel/trace/rv/monitors/irqexit/irqexit.c
 create mode 100644 kernel/trace/rv/monitors/irqexit/irqexit.h
 create mode 100644 kernel/trace/rv/monitors/irqexit/irqexit_kunit.c
 create mode 100644 kernel/trace/rv/monitors/irqexit/irqexit_kunit.h
 create mode 100644 kernel/trace/rv/monitors/irqexit/irqexit_trace.h
 create mode 100644 kernel/trace/rv/monitors/irqstate/Kconfig
 create mode 100644 kernel/trace/rv/monitors/irqstate/irqstate.c
 create mode 100644 kernel/trace/rv/monitors/irqstate/irqstate.h
 create mode 100644 kernel/trace/rv/monitors/irqstate/irqstate_kunit.c
 create mode 100644 kernel/trace/rv/monitors/irqstate/irqstate_kunit.h
 create mode 100644 kernel/trace/rv/monitors/irqstate/irqstate_trace.h
 create mode 100644 tools/verification/models/irq/irqexit.dot
 create mode 100644 tools/verification/models/irq/irqstate.dot


base-commit: 6628e7d4c6b25c8d18f1345e3a20d21829aae7e4
-- 
2.39.5 (Apple Git-154)