genirq: Add kunit tests for depth counts

genirq: Add kunit tests for depth counts

There have been a few bugs and/or misunderstandings about the reference
counting, and startup/shutdown behaviors in the IRQ core and related CPU
hotplug code. These 4 test cases try to capture a few interesting cases.

 * irq_disable_depth_test: basic request/disable/enable sequence

 * irq_free_disabled_test: request/disable/free/re-request sequence -
   this catches errors on previous revisions of my work

 * irq_cpuhotplug_test: exercises managed-affinity IRQ + CPU hotplug.
   This captures a problematic test case which was fixed recently.
   This test requires CONFIG_SMP and a hotpluggable CPU#1.

 * irq_shutdown_depth_test: exercises similar behavior from
   irq_cpuhotplug_test, but directly using irq_*() APIs instead of going
   through CPU hotplug. This still requires CONFIG_SMP, because
   managed-affinity is stubbed out (and not all APIs are even present)
   without it.

Note the use of 'imply SMP': ARCH=um doesn't support SMP, and kunit is
often exercised there. Thus, 'imply' will force SMP on where possible
(such as ARCH=x86_64), but leave it off where it's not.

Behavior on various SMP and ARCH configurations:

  $ tools/testing/kunit/kunit.py run 'irq_test_cases*' --arch x86_64 --qemu_args '-smp 2'
  [...]
  [11:12:24] Testing complete. Ran 4 tests: passed: 4

  $ tools/testing/kunit/kunit.py run 'irq_test_cases*' --arch x86_64
  [...]
  [11:13:27] [SKIPPED] irq_cpuhotplug_test
  [11:13:27] ================= [PASSED] irq_test_cases ==================
  [11:13:27] ============================================================
  [11:13:27] Testing complete. Ran 4 tests: passed: 3, skipped: 1

  # default: ARCH=um
  $ tools/testing/kunit/kunit.py run 'irq_test_cases*'
  [11:14:26] [SKIPPED] irq_shutdown_depth_test
  [11:14:26] [SKIPPED] irq_cpuhotplug_test
  [11:14:26] ================= [PASSED] irq_test_cases ==================
  [11:14:26] ============================================================
  [11:14:26] Testing complete. Ran 4 tests: passed: 2, skipped: 2

Without commit 788019eb559f ("genirq: Retain disable depth for managed
interrupts across CPU hotplug"), this fails as follows:

  [11:18:55] =============== irq_test_cases (4 subtests) ================
  [11:18:55] [PASSED] irq_disable_depth_test
  [11:18:55] [PASSED] irq_free_disabled_test
  [11:18:55]     # irq_shutdown_depth_test: EXPECTATION FAILED at kernel/irq/irq_test.c:147
  [11:18:55]     Expected desc->depth == 1, but
  [11:18:55]         desc->depth == 0 (0x0)
  [11:18:55] ------------[ cut here ]------------
  [11:18:55] Unbalanced enable for IRQ 26
  [11:18:55] WARNING: CPU: 1 PID: 36 at kernel/irq/manage.c:792 __enable_irq+0x36/0x60
  ...
  [11:18:55] [FAILED] irq_shutdown_depth_test
  [11:18:55]  #1
  [11:18:55]     # irq_cpuhotplug_test: EXPECTATION FAILED at kernel/irq/irq_test.c:202
  [11:18:55]     Expected irqd_is_activated(data) to be false, but is true
  [11:18:55]     # irq_cpuhotplug_test: EXPECTATION FAILED at kernel/irq/irq_test.c:203
  [11:18:55]     Expected irqd_is_started(data) to be false, but is true
  [11:18:55]     # irq_cpuhotplug_test: EXPECTATION FAILED at kernel/irq/irq_test.c:204
  [11:18:55]     Expected desc->depth == 1, but
  [11:18:55]         desc->depth == 0 (0x0)
  [11:18:55] ------------[ cut here ]------------
  [11:18:55] Unbalanced enable for IRQ 27
  [11:18:55] WARNING: CPU: 0 PID: 38 at kernel/irq/manage.c:792 __enable_irq+0x36/0x60
  ...
  [11:18:55] [FAILED] irq_cpuhotplug_test
  [11:18:55]     # module: irq_test
  [11:18:55] # irq_test_cases: pass:2 fail:2 skip:0 total:4
  [11:18:55] # Totals: pass:2 fail:2 skip:0 total:4
  [11:18:55] ================= [FAILED] irq_test_cases ==================
  [11:18:55] ============================================================
  [11:18:55] Testing complete. Ran 4 tests: passed: 2, failed: 2

Signed-off-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250522210837.4135244-1-briannorris@chromium.org