Re: [PATCH tty-linus] serial: Reduce spinlocked portion of uart_rs485_config()

["Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>]

On Thu, 21 Sep 2023, John Ogness wrote:

> On 2023-09-21, Lukas Wunner <lukas@wunner.de> wrote:
> > diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> > index 7bdc21d5e13b..ca26a8aef2cb 100644
> > --- a/drivers/tty/serial/serial_core.c
> > +++ b/drivers/tty/serial/serial_core.c
> > @@ -1404,12 +1404,18 @@ static void uart_set_rs485_termination(struct uart_port *port,
> >  static int uart_rs485_config(struct uart_port *port)
> >  {
> >  	struct serial_rs485 *rs485 = &port->rs485;
> > +	unsigned long flags;
> >  	int ret;
> >  
> > +	if (!(rs485->flags & SER_RS485_ENABLED))
> > +		return 0;
> > +
> >  	uart_sanitize_serial_rs485(port, rs485);
> >  	uart_set_rs485_termination(port, rs485);
> >  
> > +	spin_lock_irqsave(&port->lock, flags);
> >  	ret = port->rs485_config(port, NULL, rs485);
> > +	spin_unlock_irqrestore(&port->lock, flags);
> >  	if (ret)
> >  		memset(rs485, 0, sizeof(*rs485));
> 
> Is there some kind of guarantee that 2 CPUs cannot go into
> uart_rs485_config() simultaneously? Otherwise it seems dangerous to be
> using and clearing @port->rs485 outside of the spin_lock.

Both callers seem to be inside tty port's mutex.

-- 
 i.