USB: remove use of the bus rwsem, as it doesn't really protect anything.

The driver core stopped using the rwsem a long time ago, yet the USB
core still grabbed the lock, thinking it protected something.  This
patch removes that useless use.

Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Oliver Neukum <oneukum@suse.de>
Cc: David Brownell <david-b@pacbell.net>
Cc: linux-usb-devel <linux-usb-devel@lists.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/core/devices.c

@@ -246,7 +246,6 @@ static char *usb_dump_interface_descriptor(char *start, char *end,
 
 	if (start > end)
 		return start;
-	down_read(&usb_bus_type.subsys.rwsem);
 	if (iface) {
 		driver_name = (iface->dev.driver
 				? iface->dev.driver->name
@@ -263,7 +262,6 @@ static char *usb_dump_interface_descriptor(char *start, char *end,
 			 desc->bInterfaceSubClass,
 			 desc->bInterfaceProtocol,
 			 driver_name);
-	up_read(&usb_bus_type.subsys.rwsem);
 	return start;
 }
 

drivers/usb/core/devio.c

@@ -421,14 +421,11 @@ static int claimintf(struct dev_state *ps, unsigned int ifnum)
 	if (test_bit(ifnum, &ps->ifclaimed))
 		return 0;
 
-	/* lock against other changes to driver bindings */
-	down_write(&usb_bus_type.subsys.rwsem);
 	intf = usb_ifnum_to_if(dev, ifnum);
 	if (!intf)
 		err = -ENOENT;
 	else
 		err = usb_driver_claim_interface(&usbfs_driver, intf, ps);
-	up_write(&usb_bus_type.subsys.rwsem);
 	if (err == 0)
 		set_bit(ifnum, &ps->ifclaimed);
 	return err;
@@ -444,8 +441,6 @@ static int releaseintf(struct dev_state *ps, unsigned int ifnum)
 	if (ifnum >= 8*sizeof(ps->ifclaimed))
 		return err;
 	dev = ps->dev;
-	/* lock against other changes to driver bindings */
-	down_write(&usb_bus_type.subsys.rwsem);
 	intf = usb_ifnum_to_if(dev, ifnum);
 	if (!intf)
 		err = -ENOENT;
@@ -453,7 +448,6 @@ static int releaseintf(struct dev_state *ps, unsigned int ifnum)
 		usb_driver_release_interface(&usbfs_driver, intf);
 		err = 0;
 	}
-	up_write(&usb_bus_type.subsys.rwsem);
 	return err;
 }
 
@@ -813,7 +807,6 @@ static int proc_getdriver(struct dev_state *ps, void __user *arg)
 
 	if (copy_from_user(&gd, arg, sizeof(gd)))
 		return -EFAULT;
-	down_read(&usb_bus_type.subsys.rwsem);
 	intf = usb_ifnum_to_if(ps->dev, gd.interface);
 	if (!intf || !intf->dev.driver)
 		ret = -ENODATA;
@@ -822,7 +815,6 @@ static int proc_getdriver(struct dev_state *ps, void __user *arg)
 				sizeof(gd.driver));
 		ret = (copy_to_user(arg, &gd, sizeof(gd)) ? -EFAULT : 0);
 	}
-	up_read(&usb_bus_type.subsys.rwsem);
 	return ret;
 }
 
@@ -1351,15 +1343,12 @@ static int proc_ioctl(struct dev_state *ps, struct usbdevfs_ioctl *ctl)
 
 	/* disconnect kernel driver from interface */
 	case USBDEVFS_DISCONNECT:
-
-		down_write(&usb_bus_type.subsys.rwsem);
 		if (intf->dev.driver) {
 			driver = to_usb_driver(intf->dev.driver);
 			dev_dbg (&intf->dev, "disconnect by usbfs\n");
 			usb_driver_release_interface(driver, intf);
 		} else
 			retval = -ENODATA;
-		up_write(&usb_bus_type.subsys.rwsem);
 		break;
 
 	/* let kernel drivers try to (re)bind to the interface */
@@ -1371,7 +1360,6 @@ static int proc_ioctl(struct dev_state *ps, struct usbdevfs_ioctl *ctl)
 
 	/* talk directly to the interface's driver */
 	default:
-		down_read(&usb_bus_type.subsys.rwsem);
 		if (intf->dev.driver)
 			driver = to_usb_driver(intf->dev.driver);
 		if (driver == NULL || driver->ioctl == NULL) {
@@ -1381,7 +1369,6 @@ static int proc_ioctl(struct dev_state *ps, struct usbdevfs_ioctl *ctl)
 			if (retval == -ENOIOCTLCMD)
 				retval = -ENOTTY;
 		}
-		up_read(&usb_bus_type.subsys.rwsem);
 	}
 
 	/* cleanup and return */

drivers/usb/core/driver.c

@@ -287,9 +287,9 @@ static int usb_unbind_interface(struct device *dev)
  * way to bind to an interface is to return the private data from
  * the driver's probe() method.
  *
- * Callers must own the device lock and the driver model's usb_bus_type.subsys
- * writelock.  So driver probe() entries don't need extra locking,
- * but other call contexts may need to explicitly claim those locks.
+ * Callers must own the device lock, so driver probe() entries don't need
+ * extra locking, but other call contexts may need to explicitly claim that
+ * lock.
  */
 int usb_driver_claim_interface(struct usb_driver *driver,
 				struct usb_interface *iface, void* priv)
@@ -330,9 +330,9 @@ EXPORT_SYMBOL(usb_driver_claim_interface);
  * also causes the driver disconnect() method to be called.
  *
  * This call is synchronous, and may not be used in an interrupt context.
- * Callers must own the device lock and the driver model's usb_bus_type.subsys
- * writelock.  So driver disconnect() entries don't need extra locking,
- * but other call contexts may need to explicitly claim those locks.
+ * Callers must own the device lock, so driver disconnect() entries don't
+ * need extra locking, but other call contexts may need to explicitly claim
+ * that lock.
  */
 void usb_driver_release_interface(struct usb_driver *driver,
 					struct usb_interface *iface)

drivers/usb/core/message.c

@@ -1349,7 +1349,7 @@ static void release_interface(struct device *dev)
  *
  * This call is synchronous. The calling context must be able to sleep,
  * must own the device lock, and must not hold the driver model's USB
- * bus rwsem; usb device driver probe() methods cannot use this routine.
+ * bus mutex; usb device driver probe() methods cannot use this routine.
  *
  * Returns zero on success, or else the status code returned by the
  * underlying call that failed.  On successful completion, each interface