linux-kernel - [PATCH 4/6] USB: iowarrior: drop redundant disconnect mutex

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Message-Id: <20191009104846.5925-5-johan@kernel.org>
Date:   Wed,  9 Oct 2019 12:48:44 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Oliver Neukum <oneukum@...e.com>,
        Valentin Vidic <vvidic@...entin-vidic.from.hr>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Johan Hovold <johan@...nel.org>
Subject: [PATCH 4/6] USB: iowarrior: drop redundant disconnect mutex

Drop the redundant disconnect mutex which was introduced after the
open-disconnect race had been addressed generally in USB core by commit
d4ead16f50f9 ("USB: prevent char device open/deregister race").

Specifically, the rw-semaphore in core guarantees that all calls to
open() will have completed and that no new calls to open() will occur
after usb_deregister_dev() returns. Hence there is no need use the
driver data as an inverted disconnected flag.

Signed-off-by: Johan Hovold <johan@...nel.org>
---
 drivers/usb/misc/iowarrior.c | 17 ++---------------
 1 file changed, 2 insertions(+), 15 deletions(-)

diff --git a/drivers/usb/misc/iowarrior.c b/drivers/usb/misc/iowarrior.c
index f405fa734bcc..d844c2098e42 100644
--- a/drivers/usb/misc/iowarrior.c
+++ b/drivers/usb/misc/iowarrior.c
@@ -58,7 +58,6 @@ MODULE_LICENSE("GPL");
 static DEFINE_MUTEX(iowarrior_mutex);
 
 static struct usb_driver iowarrior_driver;
-static DEFINE_MUTEX(iowarrior_open_disc_lock);
 
 /*--------------*/
 /*     data     */
@@ -601,16 +600,13 @@ static int iowarrior_open(struct inode *inode, struct file *file)
 		return -ENODEV;
 	}
 
-	mutex_lock(&iowarrior_open_disc_lock);
 	dev = usb_get_intfdata(interface);
 	if (!dev) {
-		mutex_unlock(&iowarrior_open_disc_lock);
 		mutex_unlock(&iowarrior_mutex);
 		return -ENODEV;
 	}
 
 	mutex_lock(&dev->mutex);
-	mutex_unlock(&iowarrior_open_disc_lock);
 
 	/* Only one process can open each device, no sharing. */
 	if (dev->opened) {
@@ -842,7 +838,6 @@ static int iowarrior_probe(struct usb_interface *interface,
 	if (retval) {
 		/* something prevented us from registering this driver */
 		dev_err(&interface->dev, "Not able to get a minor for this device.\n");
-		usb_set_intfdata(interface, NULL);
 		goto error;
 	}
 
@@ -866,16 +861,8 @@ static int iowarrior_probe(struct usb_interface *interface,
  */
 static void iowarrior_disconnect(struct usb_interface *interface)
 {
-	struct iowarrior *dev;
-	int minor;
-
-	dev = usb_get_intfdata(interface);
-	mutex_lock(&iowarrior_open_disc_lock);
-	usb_set_intfdata(interface, NULL);
-
-	minor = dev->minor;
-	mutex_unlock(&iowarrior_open_disc_lock);
-	/* give back our minor - this will call close() locks need to be dropped at this point*/
+	struct iowarrior *dev = usb_get_intfdata(interface);
+	int minor = dev->minor;
 
 	usb_deregister_dev(interface, &iowarrior_class);
 
-- 
2.23.0