serial: 8250: Fix oops for port->pm on uart_change_pm()

commit dfe2aeb226fd5e19b0ee795f4f6ed8bc494c1534 upstream.

Unloading a hardware specific 8250 driver can produce error "Unable to
handle kernel paging request at virtual address" about ten seconds after
unloading the driver. This happens on uart_hangup() calling
uart_change_pm().

Turns out commit 04e82793f068 ("serial: 8250: Reinit port->pm on port
specific driver unbind") was only a partial fix. If the hardware specific
driver has initialized port->pm function, we need to clear port->pm too.
Just reinitializing port->ops does not do this. Otherwise serial8250_pm()
will call port->pm() instead of serial8250_do_pm().

Fixes: 04e82793f068 ("serial: 8250: Reinit port->pm on port specific driver unbind")
Signed-off-by: Tony Lindgren <tony@atomide.com>
Link: https://lore.kernel.org/r/20230804131553.52927-1-tony@atomide.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index d3083f19d21369c11abb9794e81d2bca8fcf0182..21a94bb750657c00f121e7b7497bceeb1732ac74 100644 (file)
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -3191,6 +3191,7 @@ void serial8250_init_port(struct uart_8250_port *up)
        struct uart_port *port = &up->port;
 
        spin_lock_init(&port->lock);
+       port->pm = NULL;
        port->ops = &serial8250_pops;
 
        up->cur_iotype = 0xFF;