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

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Message-ID: <5a5b1825-2ee7-455e-b52f-edc1a138d0dd@gmail.com>
Date: Tue, 29 Apr 2025 09:25:04 -0500
From: Carlos Bilbao <carlos.bilbao.osdev@...il.com>
To: Sean Christopherson <seanjc@...gle.com>, 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

Hello,


Sean, thanks for getting back to me so fast!


On 4/29/25 09:54, Sean Christopherson wrote:
> 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.


Agreed.


>
>> +static int panic_hlt_priority;
> Uber nit, pick one of halt or hlt.


True, will use halt.


>> +
>> +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
>>

Agree with all. Will fix in v3.


Thanks,

Carlos