Re: [PATCH] serial: 8250: Clear port->pm on port specific driver unbind

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Thu, Apr 13, 2023 at 10:03:41AM +0300, Tony Lindgren wrote:
> When we unbind a serial port hardware specific 8250 driver, the generic
> serial8250 driver takes over the port. After that we see an oops about 10
> seconds later. This can produce the following at least on some TI SoCs:
> 
> Unhandled fault: imprecise external abort (0x1406)
> Internal error: : 1406 [#1] SMP ARM
> 
> Turns out that we may still have the serial port hardware specific driver
> port->pm in use, and serial8250_pm() tries to call it after the port
> specific driver is gone:
> 
> serial8250_pm [8250_base] from uart_change_pm+0x54/0x8c [serial_base]
> uart_change_pm [serial_base] from uart_hangup+0x154/0x198 [serial_base]
> uart_hangup [serial_base] from __tty_hangup.part.0+0x328/0x37c
> __tty_hangup.part.0 from disassociate_ctty+0x154/0x20c
> disassociate_ctty from do_exit+0x744/0xaac
> do_exit from do_group_exit+0x40/0x8c
> do_group_exit from __wake_up_parent+0x0/0x1c
> 
> Let's fix the issue by clearing port->pm in serial8250_unregister_port().

Sounds to me like a fix that needs a Fixes tag.
Code wise LGTM,
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

> Signed-off-by: Tony Lindgren <tony@atomide.com>
> ---
>  drivers/tty/serial/8250/8250_core.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
> --- a/drivers/tty/serial/8250/8250_core.c
> +++ b/drivers/tty/serial/8250/8250_core.c
> @@ -1157,6 +1157,7 @@ void serial8250_unregister_port(int line)
>  		uart->port.flags &= ~UPF_BOOT_AUTOCONF;
>  		uart->port.type = PORT_UNKNOWN;
>  		uart->port.dev = &serial8250_isa_devs->dev;
> +		uart->port.pm = NULL;
>  		uart->capabilities = 0;
>  		serial8250_apply_quirks(uart);
>  		uart_add_one_port(&serial8250_reg, &uart->port);
> -- 
> 2.40.0

-- 
With Best Regards,
Andy Shevchenko