linux-kernel - Re: [PATCH v2 0/2] Introduce arch specific nmi enable, disable handlers

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Date:   Mon, 17 Oct 2016 10:25:01 -0400
From:   Don Zickus <dzickus@...hat.com>
To:     Babu Moger <babu.moger@...cle.com>
Cc:     mingo@...nel.org, akpm@...ux-foundation.org, ak@...ux.intel.com,
        jkosina@...e.cz, baiyaowei@...s.chinamobile.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,
        linux-kernel@...r.kernel.org, sam@...nborg.org
Subject: Re: [PATCH v2 0/2] Introduce arch specific nmi enable, disable
 handlers

On Thu, Oct 13, 2016 at 01:38:00PM -0700, Babu Moger wrote:
> 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.

Thanks Babu!  Looking through the code it seems appropriate with what I
suggested.  I am running it through my testsuite and things are failing.
But it is most likely my system is misconfigured.  Give me another day or so
to straighten that out.

Cheers,
Don

> 
> 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(-)
>