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[PATCH v2 0/2] Introduce arch specific nmi enable, disable handlers

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During our testing we noticed that nmi watchdogs in sparc could not be disabled or
enabled dynamically using sysctl/proc interface. Sparc uses its own arch specific
nmi watchdogs. There is a sysctl and proc interface(proc/sys/kernel/nmi_watchdog)
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.

v2:
  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 CONFIG_HARDLOCKUP_DETECTOR
  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.

v1:
 Initial version. Discussion thread here
 http://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1245427.html

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

 arch/sparc/kernel/nmi.c |   41 +++++++++++++++++++++++++++++-
 kernel/watchdog.c       |   65 +++++++++++++++++++++++++++++++---------------
 2 files changed, 84 insertions(+), 22 deletions(-)

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[PATCH v2 0/2] Introduce arch specific nmi enable, disable handlers Babu Moger <babu.moger@oracle.com> - 2016-10-13 22:40 +0200
  [PATCH v2 1/2] watchdog: Introduce arch_watchdog_nmi_enable and arch_watchdog_nmi_disable Babu Moger <babu.moger@oracle.com> - 2016-10-14 00:10 +0200
    Re: [PATCH v2 1/2] watchdog: Introduce arch_watchdog_nmi_enable and  arch_watchdog_nmi_disable Don Zickus <dzickus@redhat.com> - 2016-10-17 19:40 +0200
      Re: [PATCH v2 1/2] watchdog: Introduce arch_watchdog_nmi_enable and  arch_watchdog_nmi_disable Babu Moger <babu.moger@oracle.com> - 2016-10-18 04:50 +0200
    Re: [PATCH v2 1/2] watchdog: Introduce arch_watchdog_nmi_enable and  arch_watchdog_nmi_disable Andrew Morton <akpm@linux-foundation.org> - 2016-10-20 02:10 +0200
      Re: [PATCH v2 1/2] watchdog: Introduce arch_watchdog_nmi_enable and  arch_watchdog_nmi_disable Don Zickus <dzickus@redhat.com> - 2016-10-20 18:20 +0200
        Re: [PATCH v2 1/2] watchdog: Introduce arch_watchdog_nmi_enable and  arch_watchdog_nmi_disable Andrew Morton <akpm@linux-foundation.org> - 2016-10-21 05:30 +0200
          Re: [PATCH v2 1/2] watchdog: Introduce arch_watchdog_nmi_enable and  arch_watchdog_nmi_disable Don Zickus <dzickus@redhat.com> - 2016-10-21 17:20 +0200
            Re: [PATCH v2 1/2] watchdog: Introduce arch_watchdog_nmi_enable and  arch_watchdog_nmi_disable Andrew Morton <akpm@linux-foundation.org> - 2016-10-21 21:20 +0200
              Re: [PATCH v2 1/2] watchdog: Introduce arch_watchdog_nmi_enable and  arch_watchdog_nmi_disable Babu Moger <babu.moger@oracle.com> - 2016-10-22 00:00 +0200
                Re: [PATCH v2 1/2] watchdog: Introduce arch_watchdog_nmi_enable and  arch_watchdog_nmi_disable Don Zickus <dzickus@redhat.com> - 2016-10-24 17:30 +0200
                Re: [PATCH v2 1/2] watchdog: Introduce arch_watchdog_nmi_enable and  arch_watchdog_nmi_disable Babu Moger <babu.moger@oracle.com> - 2016-10-25 03:00 +0200
  [PATCH v2 2/2] sparc: Implement arch_watchdog_nmi_enable and arch_watchdog_nmi_disable Babu Moger <babu.moger@oracle.com> - 2016-10-14 00:30 +0200
  Re: [PATCH v2 0/2] Introduce arch specific nmi enable, disable  handlers Don Zickus <dzickus@redhat.com> - 2016-10-17 16:30 +0200

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