* Thomas Gleixner <t...@linutronix.de> wrote:
> 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(-)
Very nice work!
Modulo the open question about perf that Paul noticed:
Acked-by: Ingo Molnar <mi...@kernel.org>
Thanks,
Ingo
