linux-kernel - Re: test 1: was: Re: A Comparison of printk between upstream and linux-rt-devel

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Message-ID: <871q2b8bou.fsf@jogness.linutronix.de>
Date: Mon, 26 Aug 2024 19:02:49 +0206
From: John Ogness <john.ogness@...utronix.de>
To: Petr Mladek <pmladek@...e.com>, Derek Barbosa <debarbos@...hat.com>
Cc: pmaldek@...e.com, williams@...hat.com, tglx@...utronix.de,
 linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: test 1: was: Re: A Comparison of printk between upstream and
 linux-rt-devel

On 2024-08-26, Petr Mladek <pmladek@...e.com> wrote:
>> [  111.777491]  ? __pfx_hrtimer_wakeup+0x10/0x10
>> ** 8555 printk messages dropped **
>> [  111.807996]  ? __lruvec_stat_mod_folio+0x86/0xd0
>> 
>
> I see. I guess that the panic CPU ended in a deadlock in
> console_flush_on_panic() after it ignored the console_lock().
> Otherwise, it would have flushed the last messages and rebooted.

For the 8250, I would expect the legacy driver (even during "hope and
pray" mode) to be fairly reliable.

If this is running in QEMU, you could attach gdb and dump the backtrace
for the panic CPU and investigate some state variables. If this is
reproducible, it may be worth investigating where/why the legacy
printing is choking.

John Ogness