Ingo provided me a config that fails to compile with:

  arch/x86/built-in.o: In function
  `arch_trigger_all_cpu_backtrace': (.text+0x17e78): undefined
  reference to `apic' make: *** [.tmp_vmlinux1] Error 1

I realized I changed the compile behaviour of the nmi code by
not wrapping it with CONFIG_LOCAL_APIC.  To fix this I add a
compile check for ARCH_HAS_NMI_WATCHDOG around
arch_trigger_all_cpu_backtrace.
Signed-off-by: NDon Zickus <dzickus@redhat.com>
Cc: a.p.zijlstra@chello.nl
Cc: gorcunov@gmail.com
Cc: aris@redhat.com
LKML-Reference: <1266548212-24243-1-git-send-email-dzickus@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

The original patch was x86_64 centric.  Changed the code to make
it less so.

ested by building and running on a powerpc.
Signed-off-by: NDon Zickus <dzickus@redhat.com>
Cc: peterz@infradead.org
Cc: gorcunov@gmail.com
Cc: aris@redhat.com
LKML-Reference: <1266013161-31197-2-git-send-email-dzickus@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

This is a new generic nmi_watchdog implementation using the perf
events infrastructure as suggested by Ingo.

The implementation is simple, just create an in-kernel perf
event and register an overflow handler to check for cpu lockups.

I created a generic implementation that lives in kernel/ and
the hardware specific part that for now lives in arch/x86.

This approach has a number of advantages:

 - It simplifies the x86 PMU implementation in the long run,
   in that it removes the hardcoded low-level PMU implementation
   that was the NMI watchdog before.

 - It allows new NMI watchdog features to be added in a central
   place.

 - It allows other architectures to enable the NMI watchdog,
   as long as they have perf events (that provide NMIs)
   implemented.

 - It also allows for more graceful co-existence of existing
   perf events apps and the NMI watchdog - before these changes
   the relationship was exclusive. (The NMI watchdog will 'spend'
   a perf event when enabled. In later iterations we might be
   able to piggyback from an existing NMI event without having
   to allocate a hardware event for the NMI watchdog - turning
   this into a no-hardware-cost feature.)

As for compatibility, we'll keep the old NMI watchdog code as
well until the new one can 100% replace it on all CPUs, old and
new alike.  That might take some time as the NMI watchdog has
been ported to many CPU models.

I have done light testing to make sure the framework works
correctly and it does.

 v2: Set the correct timeout values based on the old nmi
     watchdog
Signed-off-by: NDon Zickus <dzickus@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: gorcunov@gmail.com
Cc: aris@redhat.com
Cc: peterz@infradead.org
LKML-Reference: <1265424425-31562-3-git-send-email-dzickus@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>