Re: [PATCH v9 4/6] serial: take termios_rwsem for ->rs485_config() & pass termios as param

[Jiri Slaby]

On 24. 06. 22, 22:42, Ilpo Järvinen wrote:
> To be able to alter ADDRB within ->rs485_config(), take termios_rwsem
> before calling ->rs485_config() and pass termios.

OK, FTR, worth noting the tty->termios_rwsem -> port->mutex lock chain 
is preexisting.

Anyway, I'm not sure I buy the above. Why is termios_rwsem needed to 
alter ADDRB?

> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> index 621fc15e2e54..44c3785445e3 100644
> --- a/drivers/tty/serial/serial_core.c
> +++ b/drivers/tty/serial/serial_core.c
...
> @@ -1511,6 +1511,10 @@ uart_ioctl(struct tty_struct *tty, unsigned int cmd, unsigned long arg)
>   	if (ret != -ENOIOCTLCMD)
>   		goto out;
>   
> +	/* rs485_config requires more locking than others */
> +	if (cmd == TIOCGRS485)
> +		down_write(&tty->termios_rwsem);
> +
>   	mutex_lock(&port->mutex);
>   	uport = uart_port_check(state);
>   
...
> @@ -1551,6 +1555,8 @@ uart_ioctl(struct tty_struct *tty, unsigned int cmd, unsigned long arg)
>   	}
>   out_up:
>   	mutex_unlock(&port->mutex);
> +	if (cmd == TIOCGRS485)
> +		up_write(&tty->termios_rwsem);
>   out:
>   	return ret;
>   }

thanks,
--
js