linux-kernel - Re: [v2] tty: serial_core: Fix serial console crash on port shutdown

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Date:   Wed, 19 Oct 2016 13:36:36 +0530
From:   Mugunthan V N <mugunthanvnm@...com>
To:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>
CC:     Niklas Söderlund 
        <niklas.soderlund+renesas@...natech.se>,
        Rob Herring <robh@...nel.org>,
        Peter Hurley <peter@...leysoftware.com>,
        Alan Cox <alan@...ux.intel.com>,
        <linux-serial@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [v2] tty: serial_core: Fix serial console crash on port shutdown

On Tuesday 18 October 2016 10:05 PM, Geert Uytterhoeven wrote:
> The port->console flag is always false, as uart_console() is called
> before the serial console has been registered.
> 
> Hence for a serial port used as the console, uart_tty_port_shutdown()
> will still be called when userspace closes the port, powering it down.
> This may lead to a system lock up when the serial console driver writes
> to the serial port's registers.
> 
> To fix this, move the setting of port->console after the call to
> uart_configure_port(), which registers the serial console.
> 
> Fixes: 761ed4a94582ab29 ("tty: serial_core: convert uart_close to use tty_port_close")
> Reported-by: Niklas Söderlund <niklas.soderlund+renesas@...natech.se>
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> Acked-by: Rob Herring <robh@...nel.org>

Fixes some junk characters seen on boot console on TI platforms.

Tested-by: Mugunthan V N <mugunthanvnm@...com>

Regards
Mugunthan V N

> ---
> v2:
>   - Add Acked-by,
>   - Reworded one-line summary (incl. magic word "fix").
> 
> Can easily be reproduced on Renesas boards:
>   1. With systemd: hangs during boot,
>   2. Without systemd: "telinit n" to switch to a runlevel that doesn't
>      run a getty on ttySC0, and trigger kernel console output => hang.
> ---
>  drivers/tty/serial/serial_core.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> index 6e4f63627479db8d..ce8899c13af3d97f 100644
> --- a/drivers/tty/serial/serial_core.c
> +++ b/drivers/tty/serial/serial_core.c
> @@ -2746,8 +2746,6 @@ int uart_add_one_port(struct uart_driver *drv, struct uart_port *uport)
>  	uport->cons = drv->cons;
>  	uport->minor = drv->tty_driver->minor_start + uport->line;
>  
> -	port->console = uart_console(uport);
> -
>  	/*
>  	 * If this port is a console, then the spinlock is already
>  	 * initialised.
> @@ -2761,6 +2759,8 @@ int uart_add_one_port(struct uart_driver *drv, struct uart_port *uport)
>  
>  	uart_configure_port(drv, state, uport);
>  
> +	port->console = uart_console(uport);
> +
>  	num_groups = 2;
>  	if (uport->attr_group)
>  		num_groups++;
>