linux-kernel - Re: [RFC PATCH] PM: dpm: add module param to backtrace all CPUs

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Message-ID: <pc5azqvv6bxpq4zuocjha7cmlmtowlwjapbo6uyb7pfp62fapf@lvgkhnt5vuap>
Date: Wed, 23 Jul 2025 23:22:12 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Sergey Senozhatsky <senozhatsky@...omium.org>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, 
	Pavel Machek <pavel@...nel.org>, Tomasz Figa <tfiga@...omium.org>, linux-pm@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] PM: dpm: add module param to backtrace all CPUs

On (25/07/23 12:59), Sergey Senozhatsky wrote:
> Add dpm_all_cpu_backtrace module parameter which controls
> all CPU backtrace dump before DPM panics the system.  This
> is expected to help understanding what might have caused
> device timeout.
> 
> Signed-off-by: Sergey Senozhatsky <senozhatsky@...omium.org>
> ---
>  drivers/base/power/main.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
> index dbf5456cd891..9fb943afe246 100644
> --- a/drivers/base/power/main.c
> +++ b/drivers/base/power/main.c
> @@ -34,6 +34,7 @@
>  #include <linux/cpufreq.h>
>  #include <linux/devfreq.h>
>  #include <linux/timer.h>
> +#include <linux/nmi.h>
>  
>  #include "../base.h"
>  #include "power.h"
> @@ -517,6 +518,9 @@ struct dpm_watchdog {
>  #define DECLARE_DPM_WATCHDOG_ON_STACK(wd) \
>  	struct dpm_watchdog wd
>  
> +static bool __read_mostly dpm_all_cpu_backtrace;
> +module_param(dpm_all_cpu_backtrace, bool, 0644);
> +
>  /**
>   * dpm_watchdog_handler - Driver suspend / resume watchdog handler.
>   * @t: The timer that PM watchdog depends on.
> @@ -532,8 +536,12 @@ static void dpm_watchdog_handler(struct timer_list *t)
>  	unsigned int time_left;
>  
>  	if (wd->fatal) {
> +		unsigned int this_cpu = smp_processor_id();
> +
>  		dev_emerg(wd->dev, "**** DPM device timeout ****\n");
>  		show_stack(wd->tsk, NULL, KERN_EMERG);
> +		if (dpm_all_cpu_backtrace)
> +			trigger_single_cpu_backtrace(this_cpu);

This is silly, I do apologize.  This should be

			trigger_allbutcpu_cpu_backtrace(this_cpu);

We want to backtrace all CPUs, except the current one.  A silly
copy-paste mistake.