linux-kernel - Re: [PATCH V6] panic: Move panic

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Date:   Thu, 24 Feb 2022 15:33:42 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>
Cc:     "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
        linux-kernel@...r.kernel.org, bhe@...hat.com,
        akpm@...ux-foundation.org, anton@...msg.org, ccross@...roid.com,
        dyoung@...hat.com, feng.tang@...el.com, john.ogness@...utronix.de,
        keescook@...omium.org, kernel@...ccoli.net,
        kexec@...ts.infradead.org, rostedt@...dmis.org,
        tony.luck@...el.com, vgoyal@...hat.com
Subject: Re: [PATCH V6] panic: Move panic_print before kmsg dumpers

On Wed 2022-02-23 01:27:35, Sergey Senozhatsky wrote:
> On (22/02/22 11:10), Guilherme G. Piccoli wrote:
> > On 21/02/2022 23:06, Sergey Senozhatsky wrote:
> > > On (22/02/14 11:13), Guilherme G. Piccoli wrote:
> > > [...]
> > > By additional panic_print messages you mean that panic_print_sys_info()
> > > will print everything (except PANIC_PRINT_ALL_PRINTK_MSG) twice?
> > > 
> > > Do we really need to dump everything twice? show_mem(), show_state(),
> > > ftrace_dump(DUMP_ALL). That's quite a bit of extra data.
> > > 
> > 
> > Oh no, we don't print everything twice, that'd be insane heh
> 
> My bad! I did not spot the `return` at the end of the new branch.
> 
> +       if (console_flush) {
> +               if (panic_print & PANIC_PRINT_ALL_PRINTK_MSG)
> +                       console_flush_on_panic(CONSOLE_REPLAY_ALL);
> +               return;
> +       }
> 
> Hmm. Yeah, well, that's a bit of a tricky interface now
> 
> 	panic()
> 		// everything (if corresponding bits set), no console flush
> 		panic_print_sys_info(false)
> 		...
> 		// console flush only if corresponding bit set
> 		panic_print_sys_info(true)

I agree that self-explaining names are always better than true/false.
It is pity that replay the log is handled in panic_print at all.

I sometimes hide these tricks into wrappers. We could rename:

    panic_printk_sys_info() -> panic_print_handler()

and add wrappers:

void panic_print_sys_info()
{
	panic_printk_handler(false);
}

void panic_print_log_replay()
{
	panic_printk_handler(true);
}

Or just split panic_printk_sys_info() into these two functions.

> If everyone is fine then OK.
> 
> But I _personally_ would look into changing this to something like this:
> 
> 	#define EARLY_PANIC_MASK (PANIC_PRINT_FOO | PANIC_PRINT_BAR | ...)
> 	#define LATE_PANIC_MASK (PANIC_PRINT_ALL_PRINTK_MSG)

These lists cause merge and backporting conflicts. I vote to avoid
this approach ;-)


> 	panic()
> 		panic_print_sys_info(panic_print & EARLY_PANIC_MASK)
> 		...
> 		panic_print_sys_info(panic_print & LATE_PANIC_MASK)

That said, I could live with the patch as is. I leave the decision
to Andrew. Feel free to use:

Reviewed-by: Petr Mladek <pmladek@...e.com>

Best Regards,
Petr