[RFC PATCH 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 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.

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

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

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

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/

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
-- 
2.39.5 (Apple Git-154)