linux-kernel - Re: [PATCH v2] watchdog: Add sysctl knob hardlockup

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Date:	Sun, 18 Oct 2015 13:42:16 +0100
From:	Aaron Tomlin <atomlin@...hat.com>
To:	Don Zickus <dzickus@...hat.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>, uobergfe@...hat.com,
	jkosina@...e.cz
Subject: Re: [PATCH v2] watchdog: Add sysctl knob hardlockup_panic

On Thu 2015-10-15 11:06 -0400, Don Zickus wrote:
> The only way to enable a hardlockup to panic the machine is to set
> 'nmi_watchdog=panic' on the kernel command line.
> 
> This makes it awkward for end users and folks who want to run automate tests
> (like myself).
> 
> Mimic the softlockup_panic knob and create a /proc/sys/kernel/hardlockup_panic
> knob.
> 
> Signed-off-by: Don Zickus <dzickus@...hat.com>
> 
> --
> V2 - wrap the sysctl variable with CONFIG_HARDLOCKUP_DETECTOR (kbuid bot)
> ---
>  Documentation/lockup-watchdogs.txt |  5 +++--
>  include/linux/sched.h              |  1 +
>  kernel/sysctl.c                    | 11 +++++++++++
>  kernel/watchdog.c                  |  2 +-
>  4 files changed, 16 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/lockup-watchdogs.txt b/Documentation/lockup-watchdogs.txt
> index 22dd6af..4a6e33e 100644
> --- a/Documentation/lockup-watchdogs.txt
> +++ b/Documentation/lockup-watchdogs.txt
> @@ -20,8 +20,9 @@ kernel mode for more than 10 seconds (see "Implementation" below for
>  details), without letting other interrupts have a chance to run.
>  Similarly to the softlockup case, the current stack trace is displayed
>  upon detection and the system will stay locked up unless the default
> -behavior is changed, which can be done through a compile time knob,
> -"BOOTPARAM_HARDLOCKUP_PANIC", and a kernel parameter, "nmi_watchdog"
> +behavior is changed, which can be done through a sysctl,
> +'hardlockup_panic', a compile time knob, "BOOTPARAM_HARDLOCKUP_PANIC",
> +and a kernel parameter, "nmi_watchdog"
>  (see "Documentation/kernel-parameters.txt" for details).
>  
>  The panic option can be used in combination with panic_timeout (this
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index b7b9501..5e65b14 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -384,6 +384,7 @@ extern int proc_dowatchdog_thresh(struct ctl_table *table, int write,
>  				  void __user *buffer,
>  				  size_t *lenp, loff_t *ppos);
>  extern unsigned int  softlockup_panic;
> +extern unsigned int  hardlockup_panic;
>  void lockup_detector_init(void);
>  #else
>  static inline void touch_softlockup_watchdog(void)
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index efb0370..a341117 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -887,6 +887,17 @@ static struct ctl_table kern_table[] = {
>  		.extra1		= &zero,
>  		.extra2		= &one,
>  	},
> +#ifdef CONFIG_HARDLOCKUP_DETECTOR
> +	{
> +		.procname	= "hardlockup_panic",
> +		.data		= &hardlockup_panic,
> +		.maxlen		= sizeof(int),
> +		.mode		= 0644,
> +		.proc_handler	= proc_dointvec_minmax,
> +		.extra1		= &zero,
> +		.extra2		= &one,
> +	},
> +#endif
>  #ifdef CONFIG_SMP
>  	{
>  		.procname	= "softlockup_all_cpu_backtrace",
> diff --git a/kernel/watchdog.c b/kernel/watchdog.c
> index f6b32b8..0a23125 100644
> --- a/kernel/watchdog.c
> +++ b/kernel/watchdog.c
> @@ -112,7 +112,7 @@ static unsigned long soft_lockup_nmi_warn;
>   * Should we panic when a soft-lockup or hard-lockup occurs:
>   */
>  #ifdef CONFIG_HARDLOCKUP_DETECTOR
> -static int hardlockup_panic =
> +unsigned int __read_mostly hardlockup_panic =
>  			CONFIG_BOOTPARAM_HARDLOCKUP_PANIC_VALUE;
>  static unsigned long hardlockup_allcpu_dumped;
>  /*

Reviewed-by: Aaron Tomlin <atomlin@...hat.com>

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