linux-kernel - Re: [PATCH v3 2/2] Handle flushing of CPU backtraces during panic

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Message-ID: <87y14sjp0d.fsf@jogness.linutronix.de>
Date: Mon, 19 Aug 2024 21:29:14 +0206
From: John Ogness <john.ogness@...utronix.de>
To: Petr Mladek <pmladek@...e.com>, takakura@...inux.co.jp
Cc: rostedt@...dmis.org, senozhatsky@...omium.org,
 akpm@...ux-foundation.org, bhe@...hat.com, lukas@...ner.de,
 wangkefeng.wang@...wei.com, ubizjak@...il.com, feng.tang@...el.com,
 j.granados@...sung.com, stephen.s.brennan@...cle.com,
 linux-kernel@...r.kernel.org, nishimura@...inux.co.jp, taka@...inux.co.jp
Subject: Re: [PATCH v3 2/2] Handle flushing of CPU backtraces during panic

On 2024-08-13, Petr Mladek <pmladek@...e.com> wrote:
> I would do something like:
>
> /**
>  * console_try_or_trigger_flush - try to flush consoles directly when
>  *	safe or the trigger deferred flush.
>  *
>  * Context: Any
>  */
> void console_try_or_trigger_flush(void)
> {
> 	if (!is_printk_legacy_deferred() && console_trylock())
> 		console_unlock();
> 	else
> 		defer_console_output();
> }
>
> and use it instead of printk_trigger_flush() in
> nmi_trigger_cpumask_backtrace().

Just to be clear, you are talking about removing printk_trigger_flush()
entirely and instead provide the new console_try_or_trigger_flush()?
Which then also involves updating the call sites:

lib/nmi_backtrace.c:nmi_trigger_cpumask_backtrace()
arch/powerpc/kernel/watchdog.c:watchdog_timer_interrupt()

> Well, I would postpone this patch after we finalize the patchset
> adding con->write_atomic() callback. This patch depends on it anyway
> via is_printk_legacy_deferred(). The patchset might also add
> other wrappers for flushing consoles and we have to choose some
> reasonable names.

I agree. Let's finish up the atomic series and then we can worry about
this.

John