[PATCH RFC v3 0/3] support hotplug CPUs before reboot

[Hsin-Yi Wang]

This series adds a config REBOOT_HOTPLUG_CPU which would hotplug CPUs
before reboot. Architecture code (smp_send_stop) currently would loop
through online secondary CPUs and some may call ipi functions to them.
With this config enabled, ideally we don't need smp_send_stop. But we
keep the code for those don't enable this config and as a backup if
some CPU fails to go offline before reboot.

Also enable this config for arm64 and x86 defconfig as an example.

Change from v2:
* Add another config instead of configed by CONFIG_HOTPLUG_CPU

Hsin-Yi Wang (3):
  reboot: support hotplug CPUs before reboot
  arm64: defconfig: enable REBOOT_HOTPLUG_CPU
  x86: defconfig: enable REBOOT_HOTPLUG_CPU

 arch/Kconfig                      |  6 ++++++
 arch/arm64/configs/defconfig      |  1 +
 arch/x86/configs/i386_defconfig   |  1 +
 arch/x86/configs/x86_64_defconfig |  1 +
 include/linux/cpu.h               |  3 +++
 kernel/cpu.c                      | 19 +++++++++++++++++++
 kernel/reboot.c                   |  8 ++++++++
 7 files changed, 39 insertions(+)

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2.25.0.rc1.283.g88dfdc4193-goog