From: Wen Yang <[email protected]>
We occasionally hit a lockdep "Invalid wait context" warning in
production when a reactor callback is preempted by a timer interrupt.
On interrupt exit the scheduler takes rq->__lock (LD_WAIT_SPIN) while
rv_react() still holds its wait-type-override map, which declared
LD_WAIT_FREE. On any kernel where the task context has preemption
enabled (not just CONFIG_PREEMPT_RT) this triggers a spurious lockdep
report:
[ BUG: Invalid wait context ]
1 lock held by kunit_try_catch/209:
#0: (rv_react_map-wait-type-override){+.+.}-{1:1}
kunit_try_catch/209 is trying to lock:
ffff8a743ed3e8a0 (&rq->__lock){-...}-{2:2}
This series fixes the wait type (patch 1), makes reactor registration
failures propagate (patch 2), adds support for module-based
reactors (patch 3), and adds KUnit/kselftest coverage (patch 4-5).
Changes in v5:
- Patch 1: the locking rules no longer go to
Documentation/trace/rv/monitor_synthesis.rst, which is not about
reactors (Gabriele); they are documented in code comments.
Functional code unchanged.
- Patch 2: unchanged
- Patch 3: redesigned. v4 only exported the registration helpers,
which is harmless while all in-tree reactors are built-in, but
would let a loudable reactor module be unloaded while a monitor
still refereances its react() callback. Per the suggestion in
commit 3d3800b4f7 ("rv: Remove rv_reactor's reference counter").
A new selftest (patch 5) exercises it.
- Patch 4: The test callback is kept busy for two timer ticks so
the test also passes with HZ < 200.
- Patch 5: a selftest module that registers a reactor exercises
the module pinni g end to end: rmmod must fail while a monitor
is attached.
v4: https://lore.kernel.org/lkml/[email protected]/
v3: https://lore.kernel.org/lkml/[email protected]/
v2: https://lore.kernel.org/lkml/[email protected]/
v1: https://lore.kernel.org/lkml/[email protected]/
Wen Yang (5):
rv/reactors: use LD_WAIT_SPIN as the reactor lockdep wait type
rv/reactors: propagate rv_register_reactor() error from reactor init
rv/reactors: export rv_register_reactor() and rv_unregister_reactor()
rv/reactors: add KUnit tests for reactor registration and dispatch
selftests/verification: Test loadable module-based reactor
include/linux/rv.h | 3 +
kernel/trace/rv/Kconfig | 12 ++
kernel/trace/rv/Makefile | 1 +
kernel/trace/rv/reactor_panic.c | 3 +-
kernel/trace/rv/reactor_printk.c | 3 +-
kernel/trace/rv/rv.c | 5 +
kernel/trace/rv/rv_reactors.c | 48 ++++++--
kernel/trace/rv/rv_reactors_kunit.c | 110 ++++++++++++++++++
tools/testing/selftests/verification/Makefile | 1 +
tools/testing/selftests/verification/config | 2 +
.../test.d/rv_reactor_loadable.tc | 46 ++++++++
.../verification/test_modules/Makefile | 16 +++
.../test_modules/rv_test_reactor.c | 37 ++++++
13 files changed, 276 insertions(+), 11 deletions(-)
create mode 100644 kernel/trace/rv/rv_reactors_kunit.c
create mode 100644
tools/testing/selftests/verification/test.d/rv_reactor_loadable.tc
create mode 100644 tools/testing/selftests/verification/test_modules/Makefile
create mode 100644
tools/testing/selftests/verification/test_modules/rv_test_reactor.c
base-commit: 785095112f4198de49760552374f364043c8dbdf
--
2.25.1
