[PATCH v2 0/5] Suppot hld based on Pseudo-NMI for arm64

[Lecopzer Chen]

As we already used hld internally for arm64 since 2020, there still
doesn't have a proper commit on the upstream and we badly need it.

This serise rework on 5.17-rc7 from [1] and the origin author is
Pingfan Liu <kernelfans@xxxxxxxxx>
Sumit Garg <sumit.garg@xxxxxxxxxx>

Qoute from [1]:

> Hard lockup detector is helpful to diagnose unpaired irq enable/disable.
> But the current watchdog framework can not cope with arm64 hw perf event
> easily.

> On arm64, when lockup_detector_init()->watchdog_nmi_probe(), PMU is not
> ready until device_initcall(armv8_pmu_driver_init).  And it is deeply
> integrated with the driver model and cpuhp. Hence it is hard to push the
> initialization of armv8_pmu_driver_init() before smp_init().

> But it is easy to take an opposite approach by enabling watchdog_hld to
> get the capability of PMU async. 
> The async model is achieved by expanding watchdog_nmi_probe() with
> -EBUSY, and a re-initializing work_struct which waits on a
> wait_queue_head.

[1] https://lore.kernel.org/lkml/20211014024155.15253-1-kernelfans@xxxxxxxxx/

v2:
  1. Tweak commit message in patch 01/02/04/05 
  2. Remove vobose WARN in patch 04 within watchdog core.
  3. Change from three states variable: detector_delay_init_state to
     two states variable: lockup_detector_pending_init

     Thanks Petr Mladek <pmladek@xxxxxxxx> for the idea.
     > 1.  lockup_detector_work() called before lockup_detector_check().
     >     In this case, wait_event() will wait until lockup_detector_check()
     >     clears detector_delay_pending_init and calls wake_up().

     > 2. lockup_detector_check() called before lockup_detector_work().
     >    In this case, wait_even() will immediately continue because
     >    it will see cleared detector_delay_pending_init.
  4. Add comment in code in patch 04/05 for two states variable changing.


Lecopzer Chen (4):
  kernel/watchdog: remove WATCHDOG_DEFAULT
  kernel/watchdog: change watchdog_nmi_enable() to void
  kernel/watchdog: Adapt the watchdog_hld interface for async model
  arm64: Enable perf events based hard lockup detector

Pingfan Liu (1):
  kernel/watchdog_hld: Ensure CPU-bound context when creating hardlockup
    detector event

 arch/arm64/Kconfig             |  2 +
 arch/arm64/kernel/Makefile     |  1 +
 arch/arm64/kernel/perf_event.c | 12 +++++-
 arch/sparc/kernel/nmi.c        |  8 ++--
 drivers/perf/arm_pmu.c         |  5 +++
 include/linux/nmi.h            |  5 ++-
 include/linux/perf/arm_pmu.h   |  2 +
 kernel/watchdog.c              | 67 +++++++++++++++++++++++++++++++---
 kernel/watchdog_hld.c          |  8 +++-
 9 files changed, 95 insertions(+), 15 deletions(-)

-- 
2.25.1