linux-kernel - Re: [PATCH 2/4] watchdog: introduce watchdog_suspend() and watchdog

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Message-Id: <20150804155848.97bfe8bdf86a97e166bc32d9@linux-foundation.org>
Date:	Tue, 4 Aug 2015 15:58:48 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Ulrich Obergfell <uobergfe@...hat.com>
Cc:	linux-kernel@...r.kernel.org, dzickus@...hat.com,
	atomlin@...hat.com, jolsa@...nel.org, mhocko@...e.cz,
	eranian@...gle.com, cmetcalf@...hip.com, fweisbec@...il.com
Subject: Re: [PATCH 2/4] watchdog: introduce watchdog_suspend() and
 watchdog_resume()

On Sat,  1 Aug 2015 14:49:23 +0200 Ulrich Obergfell <uobergfe@...hat.com> wrote:

> This interface can be utilized to deactivate the hard and soft lockup
> detector temporarily. Callers are expected to minimize the duration of
> deactivation. Multiple deactivations are allowed to occur in parallel
> but should be rare in practice.
> 
> ...
>
> --- a/include/linux/nmi.h
> +++ b/include/linux/nmi.h
> @@ -80,6 +80,8 @@ extern int proc_watchdog_thresh(struct ctl_table *, int ,
>  				void __user *, size_t *, loff_t *);
>  extern int proc_watchdog_cpumask(struct ctl_table *, int,
>  				 void __user *, size_t *, loff_t *);
> +extern int watchdog_suspend(void);
> +extern void watchdog_resume(void);
>  #endif
>  
>  #ifdef CONFIG_HAVE_ACPI_APEI_NMI
> diff --git a/kernel/watchdog.c b/kernel/watchdog.c
> index 5571f20..98d44b1 100644
> --- a/kernel/watchdog.c
> +++ b/kernel/watchdog.c
> @@ -67,6 +67,7 @@ unsigned long *watchdog_cpumask_bits = cpumask_bits(&watchdog_cpumask);
>  #define for_each_watchdog_cpu(cpu) \
>  	for_each_cpu_and((cpu), cpu_online_mask, &watchdog_cpumask)
>  
> +static int __read_mostly watchdog_suspended = 0;

With my compiler the "= 0" increases the size of watchdog.o data.  For
some reason by 16 bytes(!).

>  static int __read_mostly watchdog_running;
>  static u64 __read_mostly sample_period;

The relationship between watchdog_running and watchdog_suspended hurts
my brain a bit.  It appears that all watchdog_running transitions
happen under watchdog_proc_mutex so I don't think it's racy, but I
wonder if things would be simpler if these were folded into a single
up/down counter.


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