[PATCH v8 00/10] arm64: Add framework to turn an IPI as NMI

Douglas Anderson dianders at chromium.org
Thu Apr 20 08:55:54 AEST 2023

This is an attempt to resurrect Sumit's old patch series [1] that
allowed us to use the arm64 pseudo-NMI to get backtraces of CPUs and
also to round up CPUs in kdb/kgdb. The last post from Sumit that I
could find was v7, so I called this series v8. I haven't copied all of
his old changelongs here, but you can find them from the link.

Since v7, I have:
* Addressed the small amount of feedback that was there for v7.
* Rebased.
* Added a new patch that prevents us from spamming the logs with idle
* Added an extra patch to gracefully fall back to regular IPIs if
  pseudo-NMIs aren't there.

Since there appear to be a few different patches series related to
being able to use NMIs to get stack traces of crashed systems, let me
try to organize them to the best of my understanding:

a) This series. On its own, a) will (among other things) enable stack
   traces of all running processes with the soft lockup detector if
   you've enabled the sysctl "kernel.softlockup_all_cpu_backtrace". On
   its own, a) doesn't give a hard lockup detector.

b) A different recently-posted series [2] that adds a hard lockup
   detector based on perf. On its own, b) gives a stack crawl of the
   locked up CPU but no stack crawls of other CPUs (even if they're
   locked too). Together with a) + b) we get everything (full lockup
   detect, full ability to get stack crawls).

c) The old Android "buddy" hard lockup detector [3] that I'm
   considering trying to upstream. If b) lands then I believe c) would
   be redundant (at least for arm64). c) on its own is really only
   useful on arm64 for platforms that can print CPU_DBGPCSR somehow
   (see [4]). a) + c) is roughly as good as a) + b).

[1] https://lore.kernel.org/linux-arm-kernel/1604317487-14543-1-git-send-email-sumit.garg@linaro.org/
[2] https://lore.kernel.org/linux-arm-kernel/20220903093415.15850-1-lecopzer.chen@mediatek.com/
[3] https://issuetracker.google.com/172213097
[4] https://issuetracker.google.com/172213129

Changes in v8:
- dynamic_ipi_setup() and dynamic_ipi_teardown() no longer take cpu param
- dynamic_ipi_setup() and dynamic_ipi_teardown() no longer take cpu param
- Add loongarch support, too
- Removed "#ifdef CONFIG_SMP" since arm64 is always SMP
- "Tag the arm64 idle functions as __cpuidle" new for v8
- "Provide a stub kgdb_nmicallback() if !CONFIG_KGDB" new for v8
- "Fallback to a regular IPI if NMI isn't enabled" new for v8

Douglas Anderson (3):
  arm64: idle: Tag the arm64 idle functions as __cpuidle
  kgdb: Provide a stub kgdb_nmicallback() if !CONFIG_KGDB
  arm64: ipi_nmi: Fallback to a regular IPI if NMI isn't enabled

Sumit Garg (7):
  arm64: Add framework to turn IPI as NMI
  irqchip/gic-v3: Enable support for SGIs to act as NMIs
  arm64: smp: Assign and setup an IPI as NMI
  nmi: backtrace: Allow runtime arch specific override
  arm64: ipi_nmi: Add support for NMI backtrace
  kgdb: Expose default CPUs roundup fallback mechanism
  arm64: kgdb: Roundup cpus using IPI as NMI

 arch/arm/include/asm/irq.h       |   2 +-
 arch/arm/kernel/smp.c            |   3 +-
 arch/arm64/include/asm/irq.h     |   4 ++
 arch/arm64/include/asm/nmi.h     |  17 +++++
 arch/arm64/kernel/Makefile       |   2 +-
 arch/arm64/kernel/idle.c         |   4 +-
 arch/arm64/kernel/ipi_nmi.c      | 103 +++++++++++++++++++++++++++++++
 arch/arm64/kernel/kgdb.c         |  18 ++++++
 arch/arm64/kernel/smp.c          |   8 +++
 arch/loongarch/include/asm/irq.h |   2 +-
 arch/loongarch/kernel/process.c  |   3 +-
 arch/mips/include/asm/irq.h      |   2 +-
 arch/mips/kernel/process.c       |   3 +-
 arch/powerpc/include/asm/nmi.h   |   2 +-
 arch/powerpc/kernel/stacktrace.c |   3 +-
 arch/sparc/include/asm/irq_64.h  |   2 +-
 arch/sparc/kernel/process_64.c   |   4 +-
 arch/x86/include/asm/irq.h       |   2 +-
 arch/x86/kernel/apic/hw_nmi.c    |   3 +-
 drivers/irqchip/irq-gic-v3.c     |  29 ++++++---
 include/linux/kgdb.h             |  13 ++++
 include/linux/nmi.h              |  12 ++--
 kernel/debug/debug_core.c        |   8 ++-
 23 files changed, 217 insertions(+), 32 deletions(-)
 create mode 100644 arch/arm64/include/asm/nmi.h
 create mode 100644 arch/arm64/kernel/ipi_nmi.c


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