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