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Message-ID: <60678c81-27bf-6f37-bae5-ccc91d714204@kernel.org>
Date: Mon, 4 Jul 2022 08:51:52 +0200
From: Jiri Slaby <jirislaby@...nel.org>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
linux-serial@...r.kernel.org, Greg KH <gregkh@...uxfoundation.org>,
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
Vladimir Zapolskiy <vz@...ia.com>,
Russell King <linux@...linux.org.uk>,
Richard Genoud <richard.genoud@...il.com>,
Nicolas Ferre <nicolas.ferre@...rochip.com>,
Alexandre Belloni <alexandre.belloni@...tlin.com>,
Claudiu Beznea <claudiu.beznea@...rochip.com>,
Shawn Guo <shawnguo@...nel.org>,
Sascha Hauer <s.hauer@...gutronix.de>,
Pengutronix Kernel Team <kernel@...gutronix.de>,
Fabio Estevam <festevam@...il.com>,
NXP Linux Team <linux-imx@....com>,
Maxime Coquelin <mcoquelin.stm32@...il.com>,
Alexandre Torgue <alexandre.torgue@...s.st.com>,
linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
linux-stm32@...md-mailman.stormreply.com
Cc: Lukas Wunner <lukas@...ner.de>,
Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
Lino Sanfilippo <LinoSanfilippo@....de>
Subject: Re: [PATCH v9 4/6] serial: take termios_rwsem for ->rs485_config() &
pass termios as param
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
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