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Subject[V3 PATCH 0/4] Fix race issues among panic, NMI and crash_kexec
When an HA cluster software or administrator detects non-response
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 issue, this patch set does following things:

- Don't panic on NMI if the kernel has already panicked
- Extend exclusion control currently done by panic_lock to crash_kexec
- Introduce "noextnmi" boot option which masks external NMI at the
boot time (supported only for x86)

- 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

- 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()


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 noextnmi boot option

Documentation/kernel-parameters.txt | 4 ++++
arch/x86/kernel/apic/apic.c | 17 ++++++++++++++++-
arch/x86/kernel/nmi.c | 15 +++++++++++----
arch/x86/kernel/reboot.c | 11 +++++++++++
include/linux/kernel.h | 21 +++++++++++++++++++++
kernel/kexec.c | 20 ++++++++++++++++++++
kernel/panic.c | 23 ++++++++++++++++++++---
kernel/watchdog.c | 5 +++--
8 files changed, 106 insertions(+), 10 deletions(-)

Hidehiro Kawai
Hitachi, Ltd. Research & Development Group

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