[PATCH 0/3] rv/reactors: fix lockdep warning and add KUnit tests

[wen.yang@linux.dev]

From: Wen Yang <wen.yang@linux.dev>

We occasionally hit a lockdep "Invalid wait context" warning in production
environments when rv_react() callbacks are interrupted.

The bug is intermittent in production. KUnit tests with busy-wait callbacks
can reproduce it by holding the CPU long enough for a timer interrupt to fire
during rv_react(), exposing the lockdep constraint violation:

[   44.820913] =============================
[   44.820923] [ BUG: Invalid wait context ]
[   44.821137] 7.1.0-rc7-next-20260612-virtme #6 Tainted: G                 N
[   44.821203] -----------------------------
[   44.821211] kunit_try_catch/209 is trying to lock:
[   44.821244] ffff8a743ed3e8a0 (&rq->__lock){-...}-{2:2}, at: __schedule+0x102/0x13d0
[   44.821688] other info that might help us debug this:
[   44.821708] context-{5:5}
[   44.821730] 1 lock held by kunit_try_catch/209:
[   44.821745]  #0: ffffffffb6ba62c0 (rv_react_map-wait-type-override){+.+.}-{1:1}, at: rv_react+0x9d/0xf0
[   44.821803] stack backtrace:
[   44.822110] CPU: 10 UID: 0 PID: 209 Comm: kunit_try_catch Tainted: G                 N  7.1.0-rc7-next-20260612-virtme #6 PREEMPT_{RT,(full)}
[   44.822197] Tainted: [N]=TEST
[   44.822210] Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX + PIIX, arch_caps fix, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[   44.822328] Call Trace:
[   44.822377]  <TASK>
[   44.822806]  dump_stack_lvl+0x78/0xe0
[   44.822860]  __lock_acquire+0x926/0x1c90
[   44.822888]  lock_acquire+0xd3/0x310
[   44.822901]  ? __schedule+0x102/0x13d0
[   44.822919]  ? rcu_qs+0x2d/0x1a0
[   44.822954]  _raw_spin_lock_nested+0x36/0x50
[   44.822966]  ? __schedule+0x102/0x13d0
[   44.822979]  __schedule+0x102/0x13d0
[   44.822993]  ? mark_held_locks+0x40/0x70
[   44.823009]  preempt_schedule_irq+0x37/0x70
[   44.823018]  irqentry_exit+0x1da/0x8c0
[   44.823032]  asm_sysvec_apic_timer_interrupt+0x1a/0x20
[   44.823093] RIP: 0010:mock_printk_react+0x2a/0x50
[   44.823250] Code: f3 0f 1e fa 0f 1f 44 00 00 41 54 49 89 f4 55 48 89 fd 53 e8 18 8b db ff 4c 89 e6 48 89 ef 48 89 c3 e8 fa 8e ed ff eb 02 f3 90 <e8> 01 8b db ff 48 29 d8 48 3d 3f 4b 4c 00 76 ee 5b 5d 41 5c c3 cc
[   44.823303] RSP: 0018:ffffd1c3c0733d38 EFLAGS: 00000297
[   44.823332] RAX: 00000000000119f3 RBX: 0000000a74e60d1c RCX: 000000000000001f
[   44.823342] RDX: 0000000000000000 RSI: 000000003348c8a2 RDI: ffffffffc1abbfd9
[   44.823351] RBP: ffffffffb671b613 R08: 0000000000000002 R09: 0000000000000000
[   44.823359] R10: 0000000000000001 R11: 0000000000000000 R12: ffffd1c3c0733d60
[   44.823367] R13: ffffffffb575a5fd R14: ffffd1c3c0017be8 R15: ffffd1c3c00179f8
[   44.823397]  ? rv_react+0x9d/0xf0
[   44.823437]  ? mock_printk_react+0x2f/0x50
[   44.823448]  rv_react+0xb4/0xf0
[   44.823455]  ? rv_react+0x9d/0xf0
[   44.823476]  test_printk_react_called+0x83/0xb0
[   44.823486]  ? __pfx_mock_printk_react+0x10/0x10
[   44.823502]  ? __pfx_mock_printk_react+0x10/0x10
[   44.823513]  kunit_try_run_case+0x97/0x190
[   44.823534]  ? __pfx_kunit_generic_run_threadfn_adapter+0x10/0x10
[   44.823544]  kunit_generic_run_threadfn_adapter+0x21/0x40
[   44.823551]  kthread+0x124/0x160
[   44.823562]  ? __pfx_kthread+0x10/0x10
[   44.823574]  ret_from_fork+0x291/0x3b0
[   44.823585]  ? __pfx_kthread+0x10/0x10
[   44.823595]  ret_from_fork_asm+0x1a/0x30
[   44.823641]  </TASK>


Patch 1 fixes the lockdep bug by correcting rv_react()'s wait_type_inner
from LD_WAIT_CONFIG (which inherits the outer context) to LD_WAIT_SPIN
(the tightest constraint callbacks must satisfy).

Patch 2 adds KUnit tests for reactor_printk. The busy-wait in the mock
callback reproduces the timer interrupt scenario that exposes the bug.

Patch 3 adds KUnit tests for reactor_panic, exercising the panic notifier
chain without halting the system.

Tested with CONFIG_PROVE_LOCKING=y and CONFIG_KUNIT=y.


Wen Yang (3):
  rv/reactors: fix lockdep "Invalid wait context" in rv_react()
  rv/reactors: add KUnit tests for reactor_printk
  rv/reactors: add KUnit tests for reactor_panic

 kernel/trace/rv/Kconfig                |  20 ++++
 kernel/trace/rv/Makefile               |   2 +
 kernel/trace/rv/reactor_panic_kunit.c  | 106 +++++++++++++++++++++
 kernel/trace/rv/reactor_printk_kunit.c | 123 +++++++++++++++++++++++++
 kernel/trace/rv/rv_reactors.c          |   8 +-
 5 files changed, 258 insertions(+), 1 deletion(-)
 create mode 100644 kernel/trace/rv/reactor_panic_kunit.c
 create mode 100644 kernel/trace/rv/reactor_printk_kunit.c

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2.25.1