Re: [GIT PULL] TTY/Serial driver fixes for 5.5-rc3

[Sudip Mukherjee <sudipm.mukherjee@gmail.com>]

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On Mon, Dec 23, 2019 at 07:06:51AM -0500, Greg KH wrote:
> On Fri, Dec 20, 2019 at 10:08:03AM -0800, Linus Torvalds wrote:
> > On Thu, Dec 19, 2019 at 11:07 PM Greg KH <gregkh@linuxfoundation.org> wrote:
> > >
> > > The last tty core fix should resolve a long-standing bug with a race
> > > at port creation time that some people would see, and Sudip finally
> > > tracked down.
> > 
> > Hmm, looks good. But it makes me wonder if we should now try to remove
> > the second call to tty_port_link_device()?
> > 
> > Now we have a number of helpers that do that tty_port_link_device()
> > call for the driver (eg tty_port_register_device_attr_serdev(),
> > tty_port_register_device_attr(), and the just added
> > uart_add_one_port()).
> > 
> > But we also have drivers doing it by hand, and presumably we now have
> > drivers that do it through multiple paths? I guess it's harmless, but
> > it feels a bit odd. No?
> 
> It does.  I'll try to look at this after the holidays unless Sudip beats
> me to it.

The second call to tty_port_link_device() is in
tty_port_register_device_attr_serdev() and tty_port_register_device_attr()
is being called from many other places apart from uart_add_one_port().
The attached patch should be safe. I will test and send it properly unless
someone objects to it.

--
Regards
Sudip

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diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 7c2782785736..09df885442ae 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -2858,7 +2858,8 @@ int uart_add_one_port(struct uart_driver *drv, struct uart_port *uport)
 	 * setserial to be used to alter this port's parameters.
 	 */
 	tty_dev = tty_port_register_device_attr_serdev(port, drv->tty_driver,
-			uport->line, uport->dev, port, uport->tty_groups);
+			uport->line, uport->dev, port, uport->tty_groups,
+			false);
 	if (!IS_ERR(tty_dev)) {
 		device_set_wakeup_capable(tty_dev, 1);
 	} else {
diff --git a/drivers/tty/tty_port.c b/drivers/tty/tty_port.c
index 5023c85ebc6e..dc66543fa2c3 100644
--- a/drivers/tty/tty_port.c
+++ b/drivers/tty/tty_port.c
@@ -152,11 +152,12 @@ EXPORT_SYMBOL_GPL(tty_port_register_device_attr);
 struct device *tty_port_register_device_attr_serdev(struct tty_port *port,
 		struct tty_driver *driver, unsigned index,
 		struct device *device, void *drvdata,
-		const struct attribute_group **attr_grp)
+		const struct attribute_group **attr_grp, bool link)
 {
 	struct device *dev;
 
-	tty_port_link_device(port, driver, index);
+	if (link)
+		tty_port_link_device(port, driver, index);
 
 	dev = serdev_tty_port_register(port, device, driver, index);
 	if (PTR_ERR(dev) != -ENODEV) {
@@ -184,7 +185,7 @@ struct device *tty_port_register_device_serdev(struct tty_port *port,
 		struct device *device)
 {
 	return tty_port_register_device_attr_serdev(port, driver, index,
-			device, NULL, NULL);
+			device, NULL, NULL, true);
 }
 EXPORT_SYMBOL_GPL(tty_port_register_device_serdev);
 
diff --git a/include/linux/tty.h b/include/linux/tty.h
index bfa4e2ee94a9..7f2ad47ecf88 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -587,7 +587,7 @@ extern struct device *tty_port_register_device_serdev(struct tty_port *port,
 extern struct device *tty_port_register_device_attr_serdev(struct tty_port *port,
 		struct tty_driver *driver, unsigned index,
 		struct device *device, void *drvdata,
-		const struct attribute_group **attr_grp);
+		const struct attribute_group **attr_grp, bool link);
 extern void tty_port_unregister_device(struct tty_port *port,
 		struct tty_driver *driver, unsigned index);
 extern int tty_port_alloc_xmit_buf(struct tty_port *port);