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

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Date:   Thu, 14 Oct 2021 12:28:00 +0200
From:   Francesco Dolcini <francesco.dolcini@...adex.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     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

On Thu, Oct 14, 2021 at 10:01:53AM +0200, Francesco Dolcini wrote:
> 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 ...

This specific way I described here to reproduce the issue was introduced with
 a3cb39d258ef serial: core: Allow detach and attach serial device for console

that is kernel 5.9+

(Andy added to to:)

But the original report was about bind/unbind of the uart driver, I guess this is possible since
way more time.

> 
> 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