[V5 PATCH 0/4] Fix race issues among panic, NMI and crash_kexec

From: Hidehiro Kawai
Date: Fri Nov 20 2015 - 05:26:01 EST

When an HA clustering software or administrator detects unresponsiveness
of a host, they issue an NMI to the host to completely stop current
works and take a crash dump. If the kernel has already panicked
or is capturing a crash dump at that time, further NMI can cause
a crash dump failure.

Also, crash_kexec() called from oops context and panic() can
cause race conditions.

To solve these issues, this patch set does following things:

- Don't call panic() on NMI if the kernel has already panicked
- Extend exclusion control currently done by panic_lock to crash_kexec
- Introduce "apic_extnmi=none" boot option which masks external NMI
NMI at the boot time

Additionally, "apic_extnmi=all" is provieded. This option unmasks
external NMI for all CPUs. This would help cause kernel panic even if
CPU 0 can't handle an external NMI due to hang-up in NMI context
or being handled by other NMI handlers.

This patch set can be applied to current -tip tree.

- Use WRITE_ONCE() for crash_ipi_done to keep the instruction order
(PATCH 2/4)
- Address concurrent unknown/external NMI case, too (PATCH 2/4)
- Fix build errors (PATCH 3/4)
- Rename "noextnmi" boot option to "apic_extnmi" and expand its
feature (PATCH 4/4)

V4: https://lkml.org/lkml/2015/9/25/193
- Improve comments and descriptions (PATCH 1/4 to 3/4)
- Use new __crash_kexec(), no exclusion check version of crash_kexec(),
instead of checking if panic_cpu is the current cpu or not
(PATCH 3/4)

V3: https://lkml.org/lkml/2015/8/6/39
- Introduce nmi_panic() macro to reduce code duplication
- In the case of panic on NMI, don't return from NMI handlers
if another cpu already panicked

V2: https://lkml.org/lkml/2015/7/27/31
- Use atomic_cmpxchg() instead of current spin_trylock() to exclude
concurrent accesses to panic() and crash_kexec()
- Don't introduce no-lock version of panic() and crash_kexec()

V1: https://lkml.org/lkml/2015/7/22/81


Hidehiro Kawai (4):
panic/x86: Fix re-entrance problem due to panic on NMI
panic/x86: Allow cpus to save registers even if they are looping in NMI context
kexec: Fix race between panic() and crash_kexec() called directly
x86/apic: Introduce apic_extnmi boot option

Documentation/kernel-parameters.txt | 9 +++++++++
arch/x86/include/asm/apic.h | 5 +++++
arch/x86/include/asm/reboot.h | 1 +
arch/x86/kernel/apic/apic.c | 31 ++++++++++++++++++++++++++++++-
arch/x86/kernel/nmi.c | 27 ++++++++++++++++++++++-----
arch/x86/kernel/reboot.c | 28 ++++++++++++++++++++++++++++
include/linux/kernel.h | 21 +++++++++++++++++++++
include/linux/kexec.h | 2 ++
kernel/kexec_core.c | 26 +++++++++++++++++++++++++-
kernel/panic.c | 29 ++++++++++++++++++++++++-----
kernel/watchdog.c | 2 +-
11 files changed, 168 insertions(+), 13 deletions(-)

Hidehiro Kawai
Hitachi, Ltd. Research & Development Group

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