linux-kernel - [PATCH v3 0/2] Introduce arch specific nmi enable, disable handlers

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Message-Id: <1476818050-117332-1-git-send-email-babu.moger@oracle.com>
Date:   Tue, 18 Oct 2016 12:14:08 -0700
From:   Babu Moger <babu.moger@...cle.com>
To:     mingo@...nel.org, akpm@...ux-foundation.org, ak@...ux.intel.com,
        jkosina@...e.cz, baiyaowei@...s.chinamobile.com,
        dzickus@...hat.com, atomlin@...hat.com, uobergfe@...hat.com,
        tj@...nel.org, hidehiro.kawai.ez@...achi.com, johunt@...mai.com,
        davem@...emloft.net, sparclinux@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, sam@...nborg.org,
        babu.moger@...cle.com
Subject: [PATCH v3 0/2] Introduce arch specific nmi enable, disable handlers

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.

v3:
  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.

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