[RFC PATCH 00/10] CPU hotplug: stop_machine()-free CPU hotplug

["Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>]

Hi,

This patchset removes CPU hotplug's dependence on stop_machine() from the CPU
offline path and provides an alternative (set of APIs) to preempt_disable() to
prevent CPUs from going offline, which can be invoked from atomic context.

This is an RFC patchset with only a few call-sites of preempt_disable()
converted to the new APIs for now, and the main goal is to get feedback on the
design of the new atomic APIs and see if it serves as a viable replacement for
stop_machine()-free CPU hotplug.

Overview of the patches:
-----------------------

Patch 1 introduces the new APIs that can be used from atomic context, to
prevent CPUs from going offline.

Patches 2 to 6 convert various call-sites to use the new APIs.

Patches 7, 8 and 9 fix a KVM issue that comes into picture when we remove
stop_machine() from the CPU hotplug path. (Actually, patches 7 and 8 are
already in the kvm tree. Patch 9 is the fix we need, but I preserved the
other 2 as well so that the patches can apply easily without external
dependencies).

Patch 10 is the one which actually removes stop_machine() from the CPU
offline path.

Comments and suggestions welcome!

--
 Michael Wang (2):
      CPU hotplug: Introduce "stable" cpu online mask, for atomic hotplug readers
      smp, cpu hotplug: Fix smp_call_function_*() to prevent CPU offline properly

Paul E. McKenney (1):
      cpu: No more __stop_machine() in _cpu_down()

Srivatsa S. Bhat (4):
      smp, cpu hotplug: Fix on_each_cpu_*() to prevent CPU offline properly
      sched, cpu hotplug: Use stable online cpus in try_to_wake_up() & select_task_rq()
      kick_process(), cpu-hotplug: Prevent offlining of target CPU properly
      yield_to(), cpu-hotplug: Prevent offlining of other CPUs properly

Xiao Guangrong (3):
      KVM: VMX: fix invalid cpu passed to smp_call_function_single
      KVM: VMX: fix memory order between loading vmcs and clearing vmcs
      KVM: VMX: fix unsyc vmcs status when cpu is going down


  arch/x86/kvm/vmx.c      |   32 ++++++++++-
 include/linux/cpu.h     |    4 +
 include/linux/cpumask.h |    5 ++
 kernel/cpu.c            |  138 ++++++++++++++++++++++++++++++++++++++++++++++-
 kernel/sched/core.c     |   28 +++++++---
 kernel/smp.c            |   84 +++++++++++++++++------------
 6 files changed, 246 insertions(+), 45 deletions(-)



Thanks,
Srivatsa S. Bhat
IBM Linux Technology Center