(no subject)

[Francesco Dolcini]

Date: Thu, 14 Oct 2021 00:12:55 +0200
Subject: [PATCH 0/2] serial: imx: fix unbind/bind console

Hi,
here a couple of fixes to properly handle imx serial console
bind/unbind at runtime.

The patch from Stefan was already posted years ago
but never merged [1], however is still valid and it's
pretty easy to trigger the problem.

[1] https://marc.info/?l=linux-serial&m=154221779312036&w=2

Francesco Dolcini (1):
  serial: imx: disable console clocks on unregister

Stefan Agner (1):
  serial: imx: fix crash when un/re-binding console

 drivers/tty/serial/imx.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

-- 
2.25.1

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

[Francesco Dolcini]

From: Stefan Agner <stefan@agner.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@agner.ch>
Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
---
 drivers/tty/serial/imx.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 8b121cd869e9..51a9f9423b1a 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -2017,7 +2017,7 @@ imx_uart_console_write(struct console *co, const char *s, unsigned int count)
  * If the port was already initialised (eg, by a boot loader),
  * try to determine the current setup.
  */
-static void __init
+static void
 imx_uart_console_get_options(struct imx_port *sport, int *baud,
 			     int *parity, int *bits)
 {
@@ -2076,7 +2076,7 @@ imx_uart_console_get_options(struct imx_port *sport, int *baud,
 	}
 }
 
-static int __init
+static int
 imx_uart_console_setup(struct console *co, char *options)
 {
 	struct imx_port *sport;
-- 
2.25.1

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

[Greg Kroah-Hartman]

On Thu, Oct 14, 2021 at 09:10:52AM +0200, Francesco Dolcini wrote:
> From: Stefan Agner <stefan@agner.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@agner.ch>
> Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
> ---
>  drivers/tty/serial/imx.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)

What commit does this "fix"?  Should this go to stable kernels?  If so,
how far back?

> 
> diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
> index 8b121cd869e9..51a9f9423b1a 100644
> --- a/drivers/tty/serial/imx.c
> +++ b/drivers/tty/serial/imx.c
> @@ -2017,7 +2017,7 @@ imx_uart_console_write(struct console *co, const char *s, unsigned int count)
>   * If the port was already initialised (eg, by a boot loader),
>   * try to determine the current setup.
>   */
> -static void __init
> +static void
>  imx_uart_console_get_options(struct imx_port *sport, int *baud,
>  			     int *parity, int *bits)
>  {
> @@ -2076,7 +2076,7 @@ imx_uart_console_get_options(struct imx_port *sport, int *baud,
>  	}
>  }
>  
> -static int __init
> +static int
>  imx_uart_console_setup(struct console *co, char *options)

Why didn't we get a build warning about this section being called by
code that was not thrown away?  That feels odd...

thanks,

greg k-h

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

[Francesco Dolcini]

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@agner.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@agner.ch>
> > Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
> > ---
> >  drivers/tty/serial/imx.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> What commit does this "fix"?

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

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

[Uwe Kleine-König]

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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@agner.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@agner.ch>
> > > Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
> > > ---
> > >  drivers/tty/serial/imx.c | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > What commit does this "fix"?
> 
> root@colibri-imx6ull-06746657:~# cat /sys/devices/virtual/tty/console/active 
> tty1 ttymxc0
> root@colibri-imx6ull-06746657:~# echo -n N > /sys/devices/virtual/tty/console/subsystem/ttymxc0/console
> root@colibri-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.

I think this is a bigger problem not only affecting imx.c. Just look at
the output of:

	git grep -E '__init.*setup' drivers/tty/serial/

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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

[Francesco Dolcini]

Hello Uwe,

On Thu, Oct 14, 2021 at 10:10:28AM +0200, Uwe Kleine-König wrote:
> 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@agner.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@agner.ch>
> > > > Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
> > > > ---
> > > >  drivers/tty/serial/imx.c | 4 ++--
> > > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > 
> > > What commit does this "fix"?
> > 
> > root@colibri-imx6ull-06746657:~# cat /sys/devices/virtual/tty/console/active 
> > tty1 ttymxc0
> > root@colibri-imx6ull-06746657:~# echo -n N > /sys/devices/virtual/tty/console/subsystem/ttymxc0/console
> > root@colibri-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.
> 
> I think this is a bigger problem not only affecting imx.c. Just look at
> the output of:
> 
> 	git grep -E '__init.*setup' drivers/tty/serial/

I agree, but I think that all the earlyconsole stuff is not affected, so the amount of drivers
that should be fixed is less than it looks like.

Apart for that once you fix this issue you need to be sure that on the unbind/unregister path you undo
all you did in the setup, maybe for most of the drivers is nothing, but for serial/imx I had to
disable the clock there (see patch 2/2 in this patchset).

Francesco

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

[Francesco Dolcini]

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@agner.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@agner.ch>
> > > Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
> > > ---
> > >  drivers/tty/serial/imx.c | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > What commit does this "fix"?
> 
> root@colibri-imx6ull-06746657:~# cat /sys/devices/virtual/tty/console/active 
> tty1 ttymxc0
> root@colibri-imx6ull-06746657:~# echo -n N > /sys/devices/virtual/tty/console/subsystem/ttymxc0/console
> root@colibri-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

[PATCH 2/2] serial: imx: disable console clocks on unregister

[Francesco Dolcini]

During console setup imx_uart_console_setup() enables clocks, but they
are never disabled when the console is unregistered, this leads to
clk_prepare_enable() being called multiple times without a matching
clk_disable_unprepare() in case of unbind/bind.

Ensure that clock enable/disable are balanced adding
clk_disable_unprepare() in the console exit callback.

Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
---
 drivers/tty/serial/imx.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 51a9f9423b1a..90f82e6c54e4 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -2124,12 +2124,24 @@ imx_uart_console_setup(struct console *co, char *options)
 	return retval;
 }
 
+static int
+imx_uart_console_exit(struct console *co)
+{
+	struct imx_port *sport = imx_uart_ports[co->index];
+
+	clk_disable_unprepare(sport->clk_per);
+	clk_disable_unprepare(sport->clk_ipg);
+
+	return 0;
+}
+
 static struct uart_driver imx_uart_uart_driver;
 static struct console imx_uart_console = {
 	.name		= DEV_NAME,
 	.write		= imx_uart_console_write,
 	.device		= uart_console_device,
 	.setup		= imx_uart_console_setup,
+	.exit		= imx_uart_console_exit,
 	.flags		= CON_PRINTBUFFER,
 	.index		= -1,
 	.data		= &imx_uart_uart_driver,
-- 
2.25.1

[PATCH 0/2] serial: imx: fix unbind/bind console

[Francesco Dolcini]

Hi,
here a couple of fixes to properly handle imx serial console
bind/unbind at runtime.

The patch from Stefan was already posted years ago
but never merged [1], however is still valid and it's
pretty easy to trigger the problem.

[1] https://marc.info/?l=linux-serial&m=154221779312036&w=2

Francesco Dolcini (1):
  serial: imx: disable console clocks on unregister

Stefan Agner (1):
  serial: imx: fix crash when un/re-binding console

 drivers/tty/serial/imx.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

-- 
2.25.1