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 from [1] and the origin author is
Pingfan Liu [off-list ref]
Sumit Garg [off-list ref]

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.

Provide an API - retry_lockup_detector_init() for anyone who needs
to delayed init lockup detector.

The original assumption is: nobody should use delayed probe after
lockup_detector_check() (which has __init attribute).
That is, anyone uses this API must call between lockup_detector_init()
and lockup_detector_check(), and the caller must have __init attribute

The delayed init flow is:
1. lockup_detector_init() -> watchdog_nmi_probe() get non-zero retun,
   then set allow_lockup_detector_init_retry to true which means it's
   able to do delayed probe later.

2. PMU arch code init done, call retry_lockup_detector_init().

3. retry_lockup_detector_init() queue the work only when
   allow_lockup_detector_init_retry is true which means nobody should
call
   this before lockup_detector_init().

4. the work lockup_detector_delay_init() is doing without wait event.
   if probe success, set allow_lockup_detector_init_retry to false.

5. at late_initcall_sync(), lockup_detector_check() set
   allow_lockup_detector_init_retry to false first to avoid any later
retry,
   and then flush_work() to make sure the __init section won't be freed
   before the work done.

[1]
https://lore.kernel.org/lkml/20211014024155.15253-1-kernelfans@gmail.com/ (local)

v7:
  rebase on v6.0-rc3

v6:
  fix build failed reported by kernel test robot [off-list ref]
https://lore.kernel.org/lkml/20220614062835.7196-1-lecopzer.chen@mediatek.com/ (local)

v5:
  1. rebase on v5.19-rc2
  2. change to proper schedule api
  3. return value checking before retry_lockup_detector_init()
https://lore.kernel.org/lkml/20220613135956.15711-1-lecopzer.chen@mediatek.com/ (local)

v4:
  1. remove -EBUSY protocal, let all the non-zero value from
     watchdog_nmi_probe() be able to retry.
  2. separate arm64 part patch into hw_nmi_get_sample_period and retry
     delayed init
  3. tweak commit msg that we don't have to limit to -EBUSY  
  4. rebase on v5.18-rc4
https://lore.kernel.org/lkml/20220427161340.8518-1-lecopzer.chen@mediatek.com/ (local)

v3:
  1. Tweak commit message in patch 04 
	2. Remove wait event
  3. s/lockup_detector_pending_init/allow_lockup_detector_init_retry/
  4. provide api retry_lockup_detector_init() 
https://lore.kernel.org/lkml/20220324141405.10835-1-lecopzer.chen@mediatek.com/ (local) 

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: allow_lockup_detector_init_retry

     Thanks Petr Mladek [off-list ref] 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.
https://lore.kernel.org/lkml/20220307154729.13477-1-lecopzer.chen@mediatek.com/ (local)


Lecopzer Chen (5):
  kernel/watchdog: remove WATCHDOG_DEFAULT
  kernel/watchdog: change watchdog_nmi_enable() to void
  kernel/watchdog: Adapt the watchdog_hld interface for async model
  arm64: add hw_nmi_get_sample_period for preparation of lockup detector
  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/arm64/kernel/watchdog_hld.c | 39 +++++++++++++++++
 arch/sparc/kernel/nmi.c          |  8 ++--
 drivers/perf/arm_pmu.c           |  5 +++
 include/linux/nmi.h              |  4 +-
 include/linux/perf/arm_pmu.h     |  2 +
 kernel/watchdog.c                | 72 +++++++++++++++++++++++++++++---
 kernel/watchdog_hld.c            |  8 +++-
 10 files changed, 139 insertions(+), 14 deletions(-)
 create mode 100644 arch/arm64/kernel/watchdog_hld.c

-- 
2.25.1


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