linux-kernel - Re: [PATCH 1/2] serial_core: Unregister console in uart_remove_one

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Message-ID: <531E865B.9090707@hurleysoftware.com>
Date:	Mon, 10 Mar 2014 23:43:23 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>
CC:	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	linux-serial@...r.kernel.org, linux-sh@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Geert Uytterhoeven <geert+renesas@...ux-m68k.org>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
Subject: Re: [PATCH 1/2] serial_core: Unregister console in uart_remove_one_port()

On 03/10/2014 09:06 PM, Peter Hurley wrote:
> [ +cc Alan ]
>
> On 02/28/2014 08:21 AM, Geert Uytterhoeven wrote:
>> From: Geert Uytterhoeven <geert+renesas@...ux-m68k.org>
>>
>> If the serial port being removed is used as a console, it must also be
>> unregistered from the console subsystem using unregister_console().
>>
>> uart_ops.release_port() will release resources (e.g. iounmap() the serial
>> port registers), causing a crash on subsequent kernel output if the console
>> is still registered.
>
> This brings up an interesting point:  where are the serial_core drivers
> indicating to the tty core that the port is bound to a console?
> IOW, I cannot find a single 'port->console = 1' anywhere in the serial tree.

Answering half my own question: I see that serial_core doesn't use
tty_port_shutdown() but rather has it's own uart_shutdown() equivalent, and
thus doesn't use 'port->console'.

Ok.

But I still don't see what prevents a uart_port_shutdown() on a running
serial console.

Regards,
Peter Hurley

> It would be bad if the uart port disappears while a console is running
> on it...
>
>> Signed-off-by: Geert Uytterhoeven <geert+renesas@...ux-m68k.org>
>> ---
>>   drivers/tty/serial/serial_core.c |    6 ++++++
>>   1 file changed, 6 insertions(+)
>>
>> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
>> index ece2049bd270..8ece7f14d89d 100644
>> --- a/drivers/tty/serial/serial_core.c
>> +++ b/drivers/tty/serial/serial_core.c
>> @@ -2677,6 +2677,12 @@ int uart_remove_one_port(struct uart_driver *drv, struct uart_port *uport)
>>           tty_vhangup(port->tty);
>>
>>       /*
>> +     * If the port is used as a console, unregister it
>> +     */
>> +    if (uart_console(uport))
>> +        unregister_console(uport->cons);
>> +
>> +    /*
>>        * Free the port IO and memory resources, if any.
>>        */
>>       if (uport->type != PORT_UNKNOWN)
>>
>
> --
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