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Subject[PATCH v2 0/5] Suppot hld based on Pseudo-NMI for arm64
Date
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@gmail.com>
Sumit Garg <sumit.garg@linaro.org>

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@gmail.com/

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@suse.com> 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

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