During our testing we noticed that nmi watchdogs in sparc could not be disabled 
enabled dynamically using sysctl/proc interface. Sparc uses its own arch 
nmi watchdogs. There is a sysctl and proc 
to enable/disable nmi watchdogs. However, that is not working for sparc. There
is no interface to feed this parameter to arch specific nmi watchdogs.

These patches extend the same sysctl/proc interface to enable or disable
these arch specific nmi watchdogs dynamically. Introduced new functions
arch_watchdog_nmi_enable and arch_watchdog_nmi_disable which can be implemented
in arch specific handlers.
If you think there is a better way to do this. Please advice.

Tested on sparc. Compile tested on x86.

  Made one more change per Don Zickus comments.
  Moved failure path messages to into generic code inside watchdog_nmi_enable.
  Also added matching prints in sparc to warn about the failure.

  a)Sam Ravnborg's comments about making the definitions visible.
  With the new approach we dont need those definitions((NMI_WATCHDOG_ENABLED,
  SOFT_WATCHDOG_ENABLED etc..) outside watchdog.c. So no action.

  b) Made changes per Don Zickus comments.
  Don, I could not use your patches as is. Reason is sparc does not define
  CONFIG_HARDLOCKUP_DETECTOR. So, defining default __weak function did not
  work for me. However, I have used your idea to define __weak functions
  arch_watchdog_nmi_enable and arch_watchdog_nmi_disable when 
  is not defined. I feel this should have very less impact on the races you are
  concerned about. Please take a look. Feel free to suggest.

  Patch2 changes: I had to introduce new variable nmi_init_done to synchronize
  watchdog thread and kernel init thread.

 Initial version. Discussion thread here

Babu Moger (2):
  watchdog: Introduce arch_watchdog_nmi_enable and
  sparc: Implement arch_watchdog_nmi_enable and

 arch/sparc/kernel/nmi.c |   44 +++++++++++++++++++++++++++++-
 kernel/watchdog.c       |   69 +++++++++++++++++++++++++++++++---------------
 2 files changed, 89 insertions(+), 24 deletions(-)

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