Re: [PATCH] printk: handle blank console arguments passed in.

From: Guenter Roeck <linux@roeck-us.net>
To: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Petr Mladek <pmladek@suse.com>
Cc: Shreyas Joshi <shreyas.joshi@biamp.com>,
	rostedt@goodmis.org, shreyasjoshi15@gmail.com,
	linux-kernel@vger.kernel.org,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH] printk: handle blank console arguments passed in.
Date: Wed, 7 Oct 2020 08:57:06 -0700	[thread overview]
Message-ID: <be66237b-e7b2-0321-c00c-cd6fba6e3b58@roeck-us.net> (raw)
In-Reply-To: <20201007123044.GA509@jagdpanzerIV.localdomain>

On 10/7/20 5:30 AM, Sergey Senozhatsky wrote:
[ ... ]
> 
> console_on_rootfs() attempts to filp_open()->tty_open() /dev/console.
> This ends up in printk's console_device(), which iterates the list of
> console drivers and returns associated console->device back to tty. The
> problem is that console drivers list is empty, so the function returns
> NULL, and filp_open("/dev/console") fails. But the console_on_rootfs()
> comment says that this function should never fail (!). This sort of
> makes me wonder if "console=" is actually legal.
> 
I would not want to use a term such as "legal". It just happened to work
and was used.

> Hint: I can crash my laptop when I remove the "console=" boot param and
> comment out init_dup(file) calls in console_on_rootfs().
> 

I can see to options: Link /dev/console to /dev/null if there is no console,
or do something like

	if (IS_ERR(file)) {
                pr_warn("Warning: unable to open an initial console.\n");
                file = filp_open("/dev/null", O_RDWR, 0);
		if (IS_ERR(file))
                	return;
        }

Guenter