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[PATCH v2 0/7] swait: Introduce and use swq_has_sleeper()

Changes from v1: https://lkml.org/lkml/2017/9/5/622
 - Added patch 7 (mips)
 - Small comment fixlets in patch 1.


Recently[1] Nick mentioned that a lot of swait_active() callers look fishy.
This is because it inherited bad habits from regular waitqueues. Other than rcu,
kvm is one of the main callers, which I audited.

The following patches fix and/or justify (in baby steps) some of the
callers. The main exception is s390, which I didn't follow how ->valid_wakeup
can get hoisted as kvm_vcpu_block does not use that in the wait loop.


Davidlohr Bueso (7):
  sched/wait: Add swq_has_sleepers()
  kvm,async_pf: Use swq_has_sleepers()
  kvm,lapic: Justify use of swait_activate()
  kvm,x86: Fix apf_task_wake_one() wq serialization
  kvm: Serialize wq active checks in kvm_vcpu_wake_up()
  kvm,powerpc: Serialize wq active checks in ops->vcpu_kick
  kvm,mips: Fix potential swait_active() races

 arch/mips/kvm/mips.c         |  4 +--
 arch/powerpc/kvm/book3s_hv.c |  2 +-
 arch/x86/kernel/kvm.c        |  2 +-
 arch/x86/kvm/lapic.c         |  4 +++
 include/linux/swait.h        | 58 ++++++++++++++++++++++++++++++++++++++++++--
 virt/kvm/async_pf.c          |  6 +----
 virt/kvm/kvm_main.c          |  2 +-
 7 files changed, 66 insertions(+), 12 deletions(-)