linux-kernel - Re: [PATCH 1/2] watchdog: Introduce update_arch_nmi

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Date:   Fri, 7 Oct 2016 06:34:23 +0200
From:   Sam Ravnborg <sam@...nborg.org>
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,
        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,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] watchdog: Introduce update_arch_nmi_watchdog

On Thu, Oct 06, 2016 at 03:16:42PM -0700, Babu Moger wrote:
> Currently we do not have a way to enable/disable arch specific
> watchdog handlers if it was implemented by any of the architectures.
> 
> This patch introduces new function update_arch_nmi_watchdog
> which can be used to enable/disable architecture specific NMI
> watchdog handlers. Also exposes watchdog_enabled variable outside
> so that arch specific nmi watchdogs can use it to implement
> enalbe/disable behavour.
> 
> Signed-off-by: Babu Moger <babu.moger@...cle.com>
> ---
>  include/linux/nmi.h |    1 +
>  kernel/watchdog.c   |   16 +++++++++++++---
>  2 files changed, 14 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/nmi.h b/include/linux/nmi.h
> index 4630eea..01b4830 100644
> --- a/include/linux/nmi.h
> +++ b/include/linux/nmi.h
> @@ -66,6 +66,7 @@ static inline bool trigger_allbutself_cpu_backtrace(void)
>  
>  #ifdef CONFIG_LOCKUP_DETECTOR
>  u64 hw_nmi_get_sample_period(int watchdog_thresh);
> +extern unsigned long watchdog_enabled;

The extern is within an #ifdef, but the definition later is
valid alway.
So extern definition should be outside the #ifdef to match the
actual implementation.

To manipulate / read watchdog_enabled two constants are used: 
NMI_WATCHDOG_ENABLED, SOFT_WATCHDOG_ENABLED

They should be visible too, so uses do not fall into the trap
and uses constants (like in patch 2).

	Sam