linux-kernel - Re: [PATCH 1/2] serial: imx: fix crash when un/re-binding console

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Date:   Thu, 14 Oct 2021 10:01:53 +0200
From:   Francesco Dolcini <francesco.dolcini@...adex.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Francesco Dolcini <francesco.dolcini@...adex.com>,
        Jiri Slaby <jirislaby@...nel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Stefan Agner <stefan@...er.ch>, linux-serial@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] serial: imx: fix crash when un/re-binding console

Hello Greg,

On Thu, Oct 14, 2021 at 09:33:55AM +0200, Greg Kroah-Hartman wrote:
> On Thu, Oct 14, 2021 at 09:10:52AM +0200, Francesco Dolcini wrote:
> > From: Stefan Agner <stefan@...er.ch>
> > 
> > If the device used as a serial console gets un/re-binded, then
> > register_console() will call imx_uart_setup_console() again.
> > Drop __init so that imx_uart_setup_console() can be safely called
> > at runtime.
> > 
> > Signed-off-by: Stefan Agner <stefan@...er.ch>
> > Signed-off-by: Francesco Dolcini <francesco.dolcini@...adex.com>
> > ---
> >  drivers/tty/serial/imx.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> What commit does this "fix"?

root@...ibri-imx6ull-06746657:~# cat /sys/devices/virtual/tty/console/active 
tty1 ttymxc0
root@...ibri-imx6ull-06746657:~# echo -n N > /sys/devices/virtual/tty/console/subsystem/ttymxc0/console
root@...ibri-imx6ull-06746657:~# echo -n Y > /sys/devices/virtual/tty/console/subsystem/ttymxc0/console

struct console ->setup is called at that time, but imx_uart_console_setup() is gone ...

According to the original report from Stefan the issue is the same with unbind/bind of the console,
see https://marc.info/?l=linux-serial&m=154221779312036&w=2.


> Should this go to stable kernels?  If so, how far back?
This is present also in 4.19 kernel, I feel like the issue is there since it is possible to unbind
a console driver (since ever considering the current LTS releases?). I could
investigate this a little bit more.

We have this patch in our kernel branch since 3 years but for some reason we never managed to upstream it.


Francesco