[patch V3 00/32] cpu/hotplug: Convert get_online_cpus() to a percpu_rwsem

[Thomas Gleixner <tglx@linutronix.de>]

get_online_cpus() is used in hot pathes in mainline and even more so in
RT. That can show up badly under certain conditions because every locker
contends on a global mutex. RT has it's own homebrewn mitigation which is
a (badly done) open coded implementation of percpu_rwsems with recursion
support.

The proper replacement for that are percpu_rwsems, but that requires to
remove recursion support.

The conversion unearthed real locking issues which were previously not
visible because the get_online_cpus() lockdep annotation was implemented
with recursion support which prevents lockdep from tracking full dependency
chains. These potential deadlocks are not related to recursive calls, they
trigger on the first invocation because lockdep now has the full dependency
chains available.

The following patch series addresses this by

 - Cleaning up places which call get_online_cpus() nested

 - Replacing a few instances with cpu_hotplug_disable() to prevent circular
   locking dependencies.

The series is on top of 4.12-rc2. It's available in git from

   git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git WIP.hotplug

Changes since V2:

  - Reworked the approach vs. perf/ftrace/kprobes, which simplified the lot
  
  - Renamed get_online_cpus() to cpus_read_lock() to reflect the nature of
    the interface

  - Link the lockchains between hotplug control task and per cpu hotplug
    threads and fixed the fallout of that.

Thanks,

        tglx

---
 arch/arm/kernel/hw_breakpoint.c               |   11 -
 arch/arm/kernel/patch.c                       |    2 
 arch/arm/probes/kprobes/core.c                |    3 
 arch/arm64/include/asm/insn.h                 |    1 
 arch/arm64/kernel/insn.c                      |    5 
 arch/mips/kernel/jump_label.c                 |    2 
 arch/powerpc/kvm/book3s_hv.c                  |   14 -
 arch/powerpc/platforms/powernv/subcore.c      |    7 
 arch/s390/kernel/jump_label.c                 |    2 
 arch/s390/kernel/kprobes.c                    |    4 
 arch/s390/kernel/time.c                       |    6 
 arch/x86/events/core.c                        |    1 
 arch/x86/events/intel/cqm.c                   |   16 -
 arch/x86/kernel/cpu/mtrr/main.c               |    2 
 b/arch/sparc/kernel/jump_label.c              |    2 
 b/arch/tile/kernel/jump_label.c               |    2 
 b/arch/x86/events/intel/core.c                |   11 -
 b/arch/x86/kernel/jump_label.c                |    2 
 b/kernel/jump_label.c                         |   20 +-
 drivers/acpi/processor_driver.c               |    4 
 drivers/acpi/processor_throttling.c           |   16 -
 drivers/cpufreq/cpufreq.c                     |   21 +-
 drivers/hwtracing/coresight/coresight-etm3x.c |   20 +-
 drivers/hwtracing/coresight/coresight-etm4x.c |   20 +-
 drivers/pci/pci-driver.c                      |   47 +++--
 include/linux/cpu.h                           |   34 ++--
 include/linux/cpuhotplug.h                    |   38 ++++
 include/linux/padata.h                        |    3 
 include/linux/pci.h                           |    1 
 include/linux/perf_event.h                    |    2 
 include/linux/sched.h                         |   10 +
 include/linux/stop_machine.h                  |   26 ++-
 kernel/cpu.c                                  |  213 +++++++++++---------------
 kernel/events/core.c                          |  106 +++++++++---
 kernel/kprobes.c                              |   59 +++----
 kernel/padata.c                               |   43 ++---
 kernel/stop_machine.c                         |   11 -
 37 files changed, 444 insertions(+), 343 deletions(-)