linux-kernel - Re: [PATCH v2 1/2] panic: Allow for dynamic custom behavior after panic

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Message-ID: <aBDoJLyiBcSZiAHm@google.com>
Date: Tue, 29 Apr 2025 07:54:28 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: carlos.bilbao@...nel.org
Cc: tglx@...utronix.de, jan.glauber@...il.com, bilbao@...edu, pmladek@...e.com, 
	akpm@...ux-foundation.org, jani.nikula@...el.com, 
	linux-kernel@...r.kernel.org, gregkh@...uxfoundation.org, 
	takakura@...inux.co.jp, john.ogness@...utronix.de
Subject: Re: [PATCH v2 1/2] panic: Allow for dynamic custom behavior after panic

On Mon, Apr 28, 2025, carlos.bilbao@...nel.org wrote:
> diff --git a/kernel/panic.c b/kernel/panic.c
> index a3889f38153d..2cdd83b4afb6 100644
> --- a/kernel/panic.c
> +++ b/kernel/panic.c
> @@ -276,6 +276,30 @@ static void panic_other_cpus_shutdown(bool crash_kexec)
>  		crash_smp_send_stop();
>  }
>  
> +/*
> + * This is the default function called after a kernel panic has been
> + * handled. Higher priority alternatives can be set with function
> + * panic_set_handling()
> + *
> + */
> +static void after_panic_handling(void)
> +{
> +	mdelay(PANIC_TIMER_STEP);
> +}
> +
> +static void (*panic_halt)(void) = after_panic_handling;

The default implementation clearly doesn't halt, which makes this unnecessarily
confusing.  And if you're going to provide a default implementation, why bother
checking for NULL in panic()?  Just leave panic_halt NULL.

> +static int panic_hlt_priority;

Uber nit, pick one of halt or hlt.

> +
> +void panic_set_handling(void (*fn)(void), int priority)
> +{
> +	if (priority <= panic_hlt_priority)

If panic_halt is NULL by default, maybe do?

	if (panic_halt && priority <= panic_halt_priority)

> +		return;
> +
> +	panic_hlt_priority = priority;
> +	panic_halt = fn;
> +}
> +EXPORT_SYMBOL_GPL(panic_set_handling);

This doesn't seem like something that should be exported unless it's absolutely
necessary, and it shouldn't be necessary as of this series.

> +
>  /**
>   *	panic - halt the system
>   *	@fmt: The text string to print
> @@ -467,6 +491,9 @@ void panic(const char *fmt, ...)
>  	console_flush_on_panic(CONSOLE_FLUSH_PENDING);
>  	nbcon_atomic_flush_unsafe();
>  
> +	if (panic_halt)
> +		panic_halt();
> +
>  	local_irq_enable();
>  	for (i = 0; ; i += PANIC_TIMER_STEP) {
>  		touch_softlockup_watchdog();
> -- 
> 2.47.1
>