Re: [PATCH 1/1] watchdog: avoid extra sys_info dumps for all_bt

[Feng Tang]

Hi,

On Sat, Jun 20, 2026 at 10:01:40PM +0000, Bradley Morgan wrote:
> The watchdog handles SYS_INFO_ALL_BT itself. When that is the only
> watchdog specific bit, sys_info(0) falls back to kernel_sys_info.
> 
> Skip sys_info() for that case.

Thanks for the patch!

I would explain some about he intention of the global 'kernel_sys_info'
which was suggested by Andrew. One use case is, for kernel stability
issues, it could be panic, soft/hard lockup, task-hung etc, and we now
have different conrol knobs for them each, but with similar 'xxx_sys_info'
capability, and they actually need similar system info like all-cpu
dump, blocked processes dump, debug ftrace dump, using one central
'kernel_sys_info' could be very handy by avoiding setting many knobs.
And for debugging random issues, you can just add sys_info(0)
everywhere,  and controll it by the existing 'kernel_si_mask'

btw, did you meet some issues with current code? If yes, could you
agive some more details ? IIUC, when 'kernel_si_mask' is not set
specifically, sys_info(0) is a nop. 

Thanks,
Feng
 
> Fixes: a9af76a78760 ("watchdog: add sys_info sysctls to dump sys info on system lockup")
> Signed-off-by: Bradley Morgan <include@xxxxxxxxx>
> ---
>  kernel/watchdog.c | 22 ++++++++++++++++++----
>  1 file changed, 18 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/watchdog.c b/kernel/watchdog.c
> index 87dd5e0f6968..bad390a9b59e 100644
> --- a/kernel/watchdog.c
> +++ b/kernel/watchdog.c
> @@ -54,6 +54,16 @@ static int __read_mostly watchdog_hardlockup_available;
>  struct cpumask watchdog_cpumask __read_mostly;
>  unsigned long *watchdog_cpumask_bits = cpumask_bits(&watchdog_cpumask);
>  
> +static void watchdog_sys_info(unsigned long si_mask)
> +{
> +	unsigned long dump_mask = si_mask & ~SYS_INFO_ALL_BT;
> +
> +	if (si_mask && !dump_mask)
> +		return;
> +
> +	sys_info(dump_mask);
> +}
> +
>  #ifdef CONFIG_HARDLOCKUP_DETECTOR
>  
>  # ifdef CONFIG_SMP
> @@ -208,6 +218,7 @@ void watchdog_hardlockup_check(unsigned int cpu, struct pt_regs *regs)
>  {
>  	int hardlockup_all_cpu_backtrace;
>  	unsigned int this_cpu;
> +	unsigned long si_mask;
>  	unsigned long flags;
>  
>  	if (per_cpu(watchdog_hardlockup_touched, cpu)) {
> @@ -216,7 +227,8 @@ void watchdog_hardlockup_check(unsigned int cpu, struct pt_regs *regs)
>  		return;
>  	}
>  
> -	hardlockup_all_cpu_backtrace = (hardlockup_si_mask & SYS_INFO_ALL_BT) ?
> +	si_mask = READ_ONCE(hardlockup_si_mask);
> +	hardlockup_all_cpu_backtrace = (si_mask & SYS_INFO_ALL_BT) ?
>  					1 : sysctl_hardlockup_all_cpu_backtrace;
>  	/*
>  	 * Check for a hardlockup by making sure the CPU's timer
> @@ -286,7 +298,7 @@ void watchdog_hardlockup_check(unsigned int cpu, struct pt_regs *regs)
>  			clear_bit_unlock(0, &hard_lockup_nmi_warn);
>  	}
>  
> -	sys_info(hardlockup_si_mask & ~SYS_INFO_ALL_BT);
> +	watchdog_sys_info(si_mask);
>  	if (hardlockup_panic)
>  		nmi_panic(regs, "Hard LOCKUP");
>  
> @@ -798,6 +810,7 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
>  	struct pt_regs *regs = get_irq_regs();
>  	int softlockup_all_cpu_backtrace;
>  	int duration, thresh_count;
> +	unsigned long si_mask;
>  	unsigned long flags;
>  
>  	if (!watchdog_enabled)
> @@ -809,7 +822,8 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
>  	if (panic_in_progress())
>  		return HRTIMER_NORESTART;
>  
> -	softlockup_all_cpu_backtrace = (softlockup_si_mask & SYS_INFO_ALL_BT) ?
> +	si_mask = READ_ONCE(softlockup_si_mask);
> +	softlockup_all_cpu_backtrace = (si_mask & SYS_INFO_ALL_BT) ?
>  					1 : sysctl_softlockup_all_cpu_backtrace;
>  
>  	watchdog_hardlockup_kick();
> @@ -900,7 +914,7 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
>  		}
>  
>  		add_taint(TAINT_SOFTLOCKUP, LOCKDEP_STILL_OK);
> -		sys_info(softlockup_si_mask & ~SYS_INFO_ALL_BT);
> +		watchdog_sys_info(si_mask);
>  		thresh_count = duration / get_softlockup_thresh();
>  
>  		if (softlockup_panic && thresh_count >= softlockup_panic)
> -- 
> 2.53.0