linux-kernel - Re: [RFC PATCH 3/3] drm/log: Introduce a new boot logger to draw the kmsg on the screen

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <87o76czfb2.fsf@jogness.linutronix.de>
Date: Thu, 01 Aug 2024 12:57:45 +0206
From: John Ogness <john.ogness@...utronix.de>
To: Jocelyn Falempe <jfalempe@...hat.com>, Maarten Lankhorst
 <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>,
 Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>,
 Daniel Vetter <daniel@...ll.ch>, Javier Martinez Canillas
 <javierm@...hat.com>, "Guilherme G . Piccoli" <gpiccoli@...lia.com>,
 bluescreen_avenger@...izon.net, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org
Cc: Jocelyn Falempe <jfalempe@...hat.com>
Subject: Re: [RFC PATCH 3/3] drm/log: Introduce a new boot logger to draw
 the kmsg on the screen

On 2024-08-01, Jocelyn Falempe <jfalempe@...hat.com> wrote:
>  * It uses a circular buffer so the console->write() callback is very
>    quick, and will never stall.
>  * Drawing is done asynchronously using a workqueue.

For CON_NBCON, neither of the above points are necessary. You can draw
directly from the write_thread() callback. See below:

> +static bool drm_log_work_draw(void)
> +{
> +	unsigned int len;
> +	char buf[512];
> +
> +	len = drm_log_buf_read(buf, sizeof(buf));
> +	if (len)
> +		drm_log_draw_all(buf, len);
> +	return len != 0;
> +}

For CON_NBCON, this is essentially your write_thread() callback:

void drm_log_write_thread(struct console *con,
			  struct nbcon_write_context *wctxt)
{
	drm_log_draw_all(wctxt->outbuf, wctxt->len);
}

You cannot implement a write_atomic() callback because the console must
be able to print directly in NMI context and must not defer. But
write_atomic() is optional, so you should be fine there.

Disclaimer: Only in PREEMPT_RT patchset at the moment.

John Ogness