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

On Thu, 2026-10-22 at 07:07 +0200, Karl Mehltretter wrote:

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

The hardirq events 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.

Hi Karl,

thanks for your contribution!
I'm probably not going to have much time to look at this soon as I have a few
holidays planned and other series to review first. But it looks interesting.

What points my eyes is that you didn't include any schematic graph in the
documentation.
Some folks don't like RST, but I find having a textual representation of the
model there easy to understand what you're trying to do without having to build
the models.
We use graph-easy for that (and adapt things if the model is too complex).

Do not send a V2 just for this, but please keep that in mind for next time.

Thanks,
Gabriele

Cross-architecture RV KUnit testing also exposed an Arm-specific opid bug:

  https://lore.kernel.org/r/20261020035158.90190-1-kmehltretter@gmail.com (local)

I would especially appreciate feedback on:

  1. Should the context boundaries be trace events or private RV
     instrumentation?
  2. Are dedicated scheduler events the right way to follow
     preempt_schedule_irq() across task switches and migration?
  3. Should irqstate and irqexit remain separate monitors?
  4. 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 events, monitors, and documentation. Patches 6-9 add
KUnit coverage.

This series is based on v7.3 (c03c1a14507d) and depends on the following
accepted change, which is not included:

  softirq: Preserve interrupt context on return from interrupt
  https://lore.kernel.org/r/20261011060742.30584-1-kmehltretter@gmail.com (local)

A pre-existing issue can make rv_test_dummy intermittently report a
false-positive invalid-wait-context warning under lockdep. Wen Yang has
posted a fix:

 
https://lore.kernel.org/lkml/5586dd00789a0f904cc299cd8889744b8c6f8dc9.1789412799.git.wen.yang@linux.dev/ (local)

This series does not include that fix.

Karl Mehltretter (9):
  tracing/irq: Add generic IRQ context boundary events
  tracing/sched: Add IRQ preemption lifecycle events
  rv: Add a monitor for generic IRQ context transitions
  rv: Add a monitor for IRQ-exit scheduling ownership
  docs/rv: Document the IRQ-entry 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_irqentry.rst   |  398 ++++
 include/linux/interrupt.h                     |    7 +
 include/rv/kunit.h                            |   34 +-
 include/trace/events/irq.h                    |   70 +
 include/trace/events/sched.h                  |   51 +
 kernel/sched/core.c                           |    6 +
 kernel/softirq.c                              |  308 ++-
 kernel/trace/rv/Kconfig                       |    5 +
 kernel/trace/rv/Makefile                      |    3 +
 kernel/trace/rv/monitors/irqentry/Kconfig     |   13 +
 kernel/trace/rv/monitors/irqentry/irqentry.c  |   35 +
 kernel/trace/rv/monitors/irqentry/irqentry.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 |  537 +++++
 .../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     | 2062 +++++++++++++++++
 .../rv/monitors/irqstate/irqstate_kunit.h     |   25 +
 .../rv/monitors/irqstate/irqstate_trace.h     |   15 +
 kernel/trace/rv/rv_monitors_test.c            |   29 +
 kernel/trace/rv/rv_trace.h                    |    2 +
 .../verification/models/irqentry/irqexit.dot  |   21 +
 .../verification/models/irqentry/irqstate.dot |   32 +
 29 files changed, 4397 insertions(+), 13 deletions(-)
 create mode 100644 Documentation/trace/rv/monitor_irqentry.rst
 create mode 100644 kernel/trace/rv/monitors/irqentry/Kconfig
 create mode 100644 kernel/trace/rv/monitors/irqentry/irqentry.c
 create mode 100644 kernel/trace/rv/monitors/irqentry/irqentry.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/irqentry/irqexit.dot
 create mode 100644 tools/verification/models/irqentry/irqstate.dot

base-commit: c03c1a14507dfaf8b856c2608f9ac216021fc222
prerequisite-patch-id: 6ac7167f0aa7c5319dac78bf5b06a989fd7dfac5