[PATCH v5 0/6] Support hld delayed init based on Pseudo-NMI for
Lecopzer Chen
lecopzer.chen at mediatek.com
Mon Jun 13 06:59:50 PDT 2022
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 <kernelfans at gmail.com>
Sumit Garg <sumit.garg at 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.
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/
v5:
1. rebase on v5.19-rc2
2. change to proper schedule api
3. return value checking before retry_lockup_detector_init()
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
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/
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 <pmladek at 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.
https://lore.kernel.org/lkml/20220307154729.13477-1-lecopzer.chen@mediatek.com/
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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