linux-kernel - Re: [BUG] Threaded printk breaks early debugging

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Date:   Tue, 14 Jun 2022 10:38:57 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Peter Geis <pgwipeout@...il.com>
Cc:     John Ogness <john.ogness@...utronix.de>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>
Subject: Re: [BUG] Threaded printk breaks early debugging

On Mon 2022-06-13 18:20:03, Peter Geis wrote:
> On Mon, Jun 13, 2022 at 11:11 AM Petr Mladek <pmladek@...e.com> wrote:
> >
> > On Mon 2022-06-13 04:29:50, John Ogness wrote:
> > > On 2022-06-12, Peter Geis <pgwipeout@...il.com> wrote:
> > > > The buffer isn't an issue here, everything is available in dmesg when
> > > > userspace becomes available. Instead some messages bound for the
> > > > serial console are never output.
> > >
> > > OK. Good to know.
> > >
> > > > We run a serial console at 1.5m baud which is significantly higher
> > > > than most SoCs which default to 115200. I have noticed some timing
> > > > differences since the introduction of the threaded console. A
> > > > significant amount of information is dumped very early in the boot
> > > > process (between 0 and 4 seconds into boot), as most drivers are
> > > > probing during this time. It also happens to be when the earlycon
> > > > console hands over to the normal console. There is no abnormal
> > > > debugging enabled, the output is a standard (non-quiet) boot log. The
> > > > question is why is direct mode not triggering during a panic?
> > >
> > > Just to be clear, you are not losing any intermediate messages. Only the
> > > tail end of the kernel log was never printed. Is this correct?
> > >
> > > This may be the same issue being discussed here [0].
> > >
> > > John Ogness
> > >
> > > [0] https://lore.kernel.org/all/87v8t5l39z.fsf@jogness.linutronix.de
> >
> > If the last messages are missing then it is most likely the same
> > issue.
> >
> > Peter, could you please try if the patch at
> > https://lore.kernel.org/r/YqdSw/fJvnkRbjvc@alley
> > would make any difference?
> 
> This patch permits the panic to come through to the console port. Thank you!
> Tested-by: Peter Geis <pgwipeout@...il.com>

Great news. Thanks a lot for feedback.

I guess that the patch is not final. But it seems to be a good
direction.

Best Regards,
Petr