linux-kernel - Re: [PATCH V2 5/5] panic: add note that panic

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Message-ID: <aFlxLK8f276_5TZf@pathway.suse.cz>
Date: Mon, 23 Jun 2025 17:22:20 +0200
From: Petr Mladek <pmladek@...e.com>
To: Feng Tang <feng.tang@...ux.alibaba.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Lance Yang <lance.yang@...ux.dev>, Jonathan Corbet <corbet@....net>,
	linux-kernel@...r.kernel.org, paulmck@...nel.org,
	john.ogness@...utronix.de
Subject: Re: [PATCH V2 5/5] panic: add note that panic_print interface is
 deprecated

On Mon 2025-06-16 09:08:40, Feng Tang wrote:
> Long term wise, the 'panic_sys_info' should be the only controlling
> interface, which can be referred by other modules.

Strictly speaking, 'panic_sys_info' is not a complete
replacement for 'panic_print' because it does not allow
replaying the log buffer during panic.

I suggest to add a separate parameter "panic_console_replay"
for the missing functionality first. And 'panic_print' will
be obsoleted by both 'panic_sys_info' and 'panic_console_replay'.

> --- a/kernel/panic.c
> +++ b/kernel/panic.c
> @@ -76,6 +76,13 @@ ATOMIC_NOTIFIER_HEAD(panic_notifier_list);
>  EXPORT_SYMBOL(panic_notifier_list);
>  
>  #ifdef CONFIG_SYSCTL
> +static int sysctl_panic_print_handler(const struct ctl_table *table, int write,
> +			   void *buffer, size_t *lenp, loff_t *ppos)
> +{
> +	printk_once("panic: 'panic_print' sysctl interface will be obsoleted by 'panic_sys_info' interface.\n");
> +	return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
> +}
> +
>  static const struct ctl_table kern_panic_table[] = {
>  #ifdef CONFIG_SMP
>  	{
> @@ -107,7 +114,7 @@ static const struct ctl_table kern_panic_table[] = {
>  		.data		= &panic_print,
>  		.maxlen		= sizeof(unsigned long),
>  		.mode		= 0644,
> -		.proc_handler	= proc_doulongvec_minmax,
> +		.proc_handler	= sysctl_panic_print_handler,

This handles only the sysctl interface. We should do something similar
also for the "panic_print" command line parameter. It would require
using core_param_cb() instead of core_param().

>  	},
>  	{
>  		.procname	= "panic_on_warn",

Best Regards,
Petr