[PATCH] USB: Remove USB private semaphore

This patch (as605) removes the private udev->serialize semaphore,
relying instead on the locking provided by the embedded struct device's
semaphore. The changes are confined to the core, except that the
usb_trylock_device routine now uses the return convention of
down_trylock rather than down_read_trylock (they return opposite values
for no good reason).

A couple of other associated changes are included as well:

Now that we aren't concerned about HCDs that avoid using the
hcd glue layer, usb_disconnect no longer needs to acquire the
usb_bus_lock -- that can be done by usb_remove_hcd where it
belongs.

Devices aren't locked over the same scope of code in
usb_new_device and hub_port_connect_change as they used to be.
This shouldn't cause any trouble.

Along with the preceding driver core patch, this needs a lot of testing.

Signed-off-by: Alan Stern <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/core/devices.c

···
 		struct usb_device *childdev = usbdev->children[chix];
 
 		if (childdev) {
-			down(&childdev->serialize);
+			usb_lock_device(childdev);
 			ret = usb_device_dump(buffer, nbytes, skip_bytes, file_offset, childdev,
 					bus, level + 1, chix, ++cnt);
-			up(&childdev->serialize);
+			usb_unlock_device(childdev);
 			if (ret == -EFAULT)
 				return total_written;
 			total_written += ret;

drivers/usb/core/devio.c

···
 	/* let kernel drivers try to (re)bind to the interface */
 	case USBDEVFS_CONNECT:
 		usb_unlock_device(ps->dev);
-		usb_lock_all_devices();
 		bus_rescan_devices(intf->dev.bus);
-		usb_unlock_all_devices();
 		usb_lock_device(ps->dev);
 		break;
 

drivers/usb/core/driver.c

···
 	spin_lock_init(&new_driver->dynids.lock);
 	INIT_LIST_HEAD(&new_driver->dynids.list);
 
-	usb_lock_all_devices();
 	retval = driver_register(&new_driver->driver);
-	usb_unlock_all_devices();
 
 	if (!retval) {
 		pr_info("%s: registered new driver %s\n",
···
 {
 	pr_info("%s: deregistering driver %s\n", usbcore_name, driver->name);
 
-	usb_lock_all_devices();
 	usb_remove_newid_file(driver);
 	usb_free_dynids(driver);
 	driver_unregister(&driver->driver);
-	usb_unlock_all_devices();
 
 	usbfs_update_special();
 }

drivers/usb/core/hcd.c

···
 		return (retval < 0) ? retval : -EMSGSIZE;
 	}
 
-	usb_lock_device (usb_dev);
 	retval = usb_new_device (usb_dev);
-	usb_unlock_device (usb_dev);
 	if (retval) {
 		usb_dev->bus->root_hub = NULL;
 		dev_err (parent_dev, "can't register root hub for %s, %d\n",
···
 	spin_lock_irq (&hcd_root_hub_lock);
 	hcd->rh_registered = 0;
 	spin_unlock_irq (&hcd_root_hub_lock);
+
+	down(&usb_bus_list_lock);
 	usb_disconnect(&hcd->self.root_hub);
+	up(&usb_bus_list_lock);
 
 	hcd->poll_rh = 0;
 	del_timer_sync(&hcd->rh_timer);

drivers/usb/core/hub.c

···
 #include "hub.h"
 
 /* Protect struct usb_device->state and ->children members
- * Note: Both are also protected by ->serialize, except that ->state can
+ * Note: Both are also protected by ->dev.sem, except that ->state can
  * change to USB_STATE_NOTATTACHED even when the semaphore isn't held. */
 static DEFINE_SPINLOCK(device_state_lock);
 
···
 			/* when everyone grabs locks top->bottom,
 			 * non-overlapping work may be concurrent
 			 */
-			down(&udev->serialize);
-			up(&hdev->serialize);
+			usb_lock_device(udev);
+			usb_unlock_device(hdev);
 			return t + 1;
 		}
 	}
···
 	 * this quiesces everyting except pending urbs.
 	 */
 	usb_set_device_state(udev, USB_STATE_NOTATTACHED);
-
-	/* lock the bus list on behalf of HCDs unregistering their root hubs */
-	if (!udev->parent) {
-		down(&usb_bus_list_lock);
-		usb_lock_device(udev);
-	} else
-		down(&udev->serialize);
-
 	dev_info (&udev->dev, "USB disconnect, address %d\n", udev->devnum);
+
+	usb_lock_device(udev);
 
 	/* Free up all the children before we remove this device */
 	for (i = 0; i < USB_MAXCHILDREN; i++) {
···
 	*pdev = NULL;
 	spin_unlock_irq(&device_state_lock);
 
-	if (!udev->parent) {
-		usb_unlock_device(udev);
-		up(&usb_bus_list_lock);
-	} else
-		up(&udev->serialize);
+	usb_unlock_device(udev);
 
 	device_unregister(&udev->dev);
 }
···
  *
  * This is called with devices which have been enumerated, but not yet
  * configured.  The device descriptor is available, but not descriptors
- * for any device configuration.  The caller must have locked udev and
- * either the parent hub (if udev is a normal device) or else the
+ * for any device configuration.  The caller must have locked either
+ * the parent hub (if udev is a normal device) or else the
  * usb_bus_list_lock (if udev is a root hub).  The parent's pointer to
  * udev has already been installed, but udev is not yet visible through
  * sysfs or other filesystem code.
···
  *
  * This call is synchronous, and may not be used in an interrupt context.
  *
- * Only the hub driver should ever call this; root hub registration
- * uses it indirectly.
+ * Only the hub driver or root-hub registrar should ever call this.
  */
 int usb_new_device(struct usb_device *udev)
 {
···
 	}
 	usb_create_sysfs_dev_files (udev);
 
+	usb_lock_device(udev);
+
 	/* choose and set the configuration. that registers the interfaces
 	 * with the driver core, and lets usb device drivers bind to them.
 	 */
···
 
 	/* USB device state == configured ... usable */
 	usb_notify_add_device(udev);
+
+	usb_unlock_device(udev);
 
 	return 0;
 
···
 	usb_unlock_device(udev);
 
 	/* rebind drivers that had no suspend() */
-	if (status == 0) {
-		usb_lock_all_devices();
+	if (status == 0)
 		bus_rescan_devices(&usb_bus_type);
-		usb_unlock_all_devices();
-	}
 	return status;
 }
 
···
 	/* don't repeat RESUME sequence if this device
 	 * was already woken up by some other task
 	 */
-	down(&udev->serialize);
+	usb_lock_device(udev);
 	if (udev->state == USB_STATE_SUSPENDED) {
 		dev_dbg(&udev->dev, "RESUME (wakeup)\n");
 		/* TRSMRCY = 10 msec */
 		msleep(10);
 		status = finish_device_resume(udev);
 	}
-	up(&udev->serialize);
+	usb_unlock_device(udev);
 #endif
 	return status;
 }
···
 
 		if (!udev || status < 0)
 			continue;
-		down (&udev->serialize);
+		usb_lock_device(udev);
 		if (portstat & USB_PORT_STAT_SUSPEND)
 			status = hub_port_resume(hub, port1, udev);
 		else {
···
 				hub_port_logical_disconnect(hub, port1);
 			}
 		}
-		up(&udev->serialize);
+		usb_unlock_device(udev);
 	}
 	}
 #endif
···
 		 * udev becomes globally accessible, although presumably
 		 * no one will look at it until hdev is unlocked.
 		 */
-		down (&udev->serialize);
 		status = 0;
 
 		/* We mustn't add new devices if the parent hub has
···
 			}
 		}
 
-		up (&udev->serialize);
 		if (status)
 			goto loop_disable;
 

drivers/usb/core/usb.c

···
 #include <linux/spinlock.h>
 #include <linux/errno.h>
 #include <linux/smp_lock.h>
-#include <linux/rwsem.h>
 #include <linux/usb.h>
 
 #include <asm/io.h>
···
 
 static int nousb;	/* Disable USB when built into kernel image */
 			/* Not honored on modular build */
-
-static DECLARE_RWSEM(usb_all_devices_rwsem);
 
 
 /**
···
 	dev->parent = parent;
 	INIT_LIST_HEAD(&dev->filelist);
 
-	init_MUTEX(&dev->serialize);
-
 	return dev;
 }
 
···
 
 /*			USB device locking
  *
- * Although locking USB devices should be straightforward, it is
- * complicated by the way the driver-model core works.  When a new USB
- * driver is registered or unregistered, the core will automatically
- * probe or disconnect all matching interfaces on all USB devices while
- * holding the USB subsystem writelock.  There's no good way for us to
- * tell which devices will be used or to lock them beforehand; our only
- * option is to effectively lock all the USB devices.
- *
- * We do that by using a private rw-semaphore, usb_all_devices_rwsem.
- * When locking an individual device you must first acquire the rwsem's
- * readlock.  When a driver is registered or unregistered the writelock
- * must be held.  These actions are encapsulated in the subroutines
- * below, so all a driver needs to do is call usb_lock_device() and
- * usb_unlock_device().
+ * USB devices and interfaces are locked using the semaphore in their
+ * embedded struct device.  The hub driver guarantees that whenever a
+ * device is connected or disconnected, drivers are called with the
+ * USB device locked as well as their particular interface.
  *
  * Complications arise when several devices are to be locked at the same
  * time.  Only hub-aware drivers that are part of usbcore ever have to
- * do this; nobody else needs to worry about it.  The problem is that
- * usb_lock_device() must not be called to lock a second device since it
- * would acquire the rwsem's readlock reentrantly, leading to deadlock if
- * another thread was waiting for the writelock.  The solution is simple:
- *
- *	When locking more than one device, call usb_lock_device()
- *	to lock the first one.  Lock the others by calling
- *	down(&udev->serialize) directly.
- *
- *	When unlocking multiple devices, use up(&udev->serialize)
- *	to unlock all but the last one.  Unlock the last one by
- *	calling usb_unlock_device().
+ * do this; nobody else needs to worry about it.  The rule for locking
+ * is simple:
  *
  *	When locking both a device and its parent, always lock the
  *	the parent first.
  */
-
-/**
- * usb_lock_device - acquire the lock for a usb device structure
- * @udev: device that's being locked
- *
- * Use this routine when you don't hold any other device locks;
- * to acquire nested inner locks call down(&udev->serialize) directly.
- * This is necessary for proper interaction with usb_lock_all_devices().
- */
-void usb_lock_device(struct usb_device *udev)
-{
-	down_read(&usb_all_devices_rwsem);
-	down(&udev->serialize);
-}
-
-/**
- * usb_trylock_device - attempt to acquire the lock for a usb device structure
- * @udev: device that's being locked
- *
- * Don't use this routine if you already hold a device lock;
- * use down_trylock(&udev->serialize) instead.
- * This is necessary for proper interaction with usb_lock_all_devices().
- *
- * Returns 1 if successful, 0 if contention.
- */
-int usb_trylock_device(struct usb_device *udev)
-{
-	if (!down_read_trylock(&usb_all_devices_rwsem))
-		return 0;
-	if (down_trylock(&udev->serialize)) {
-		up_read(&usb_all_devices_rwsem);
-		return 0;
-	}
-	return 1;
-}
 
 /**
  * usb_lock_device_for_reset - cautiously acquire the lock for a
···
 		}
 	}
 
-	while (!usb_trylock_device(udev)) {
+	while (usb_trylock_device(udev) != 0) {
 
 		/* If we can't acquire the lock after waiting one second,
 		 * we're probably deadlocked */
···
 			return -EINTR;
 	}
 	return 1;
-}
-
-/**
- * usb_unlock_device - release the lock for a usb device structure
- * @udev: device that's being unlocked
- *
- * Use this routine when releasing the only device lock you hold;
- * to release inner nested locks call up(&udev->serialize) directly.
- * This is necessary for proper interaction with usb_lock_all_devices().
- */
-void usb_unlock_device(struct usb_device *udev)
-{
-	up(&udev->serialize);
-	up_read(&usb_all_devices_rwsem);
-}
-
-/**
- * usb_lock_all_devices - acquire the lock for all usb device structures
- *
- * This is necessary when registering a new driver or probing a bus,
- * since the driver-model core may try to use any usb_device.
- */
-void usb_lock_all_devices(void)
-{
-	down_write(&usb_all_devices_rwsem);
-}
-
-/**
- * usb_unlock_all_devices - release the lock for all usb device structures
- */
-void usb_unlock_all_devices(void)
-{
-	up_write(&usb_all_devices_rwsem);
 }
 
 
···
 	/* look through all of the children of this device */
 	for (child = 0; child < dev->maxchild; ++child) {
 		if (dev->children[child]) {
-			down(&dev->children[child]->serialize);
+			usb_lock_device(dev->children[child]);
 			ret_dev = match_device(dev->children[child],
 					       vendor_id, product_id);
-			up(&dev->children[child]->serialize);
+			usb_unlock_device(dev->children[child]);
 			if (ret_dev)
 				goto exit;
 		}
···
 EXPORT_SYMBOL(usb_get_dev);
 EXPORT_SYMBOL(usb_hub_tt_clear_buffer);
 
-EXPORT_SYMBOL(usb_lock_device);
-EXPORT_SYMBOL(usb_trylock_device);
 EXPORT_SYMBOL(usb_lock_device_for_reset);
-EXPORT_SYMBOL(usb_unlock_device);
 
 EXPORT_SYMBOL(usb_driver_claim_interface);
 EXPORT_SYMBOL(usb_driver_release_interface);

drivers/usb/core/usb.h

···
 extern char *usb_cache_string(struct usb_device *udev, int index);
 extern int usb_set_configuration(struct usb_device *dev, int configuration);
 
-extern void usb_lock_all_devices(void);
-extern void usb_unlock_all_devices(void);
-
 extern void usb_kick_khubd(struct usb_device *dev);
 extern void usb_suspend_root_hub(struct usb_device *hdev);
 extern void usb_resume_root_hub(struct usb_device *dev);

drivers/usb/host/ohci-hub.c

···
 					& ohci->hc_control)
 				== OHCI_USB_OPER
 			&& time_after (jiffies, ohci->next_statechange)
-			&& usb_trylock_device (hcd->self.root_hub)
+			&& usb_trylock_device (hcd->self.root_hub) == 0
 			) {
 		ohci_vdbg (ohci, "autosuspend\n");
 		(void) ohci_bus_suspend (hcd);

include/linux/usb.h

···
 	struct usb_tt	*tt; 		/* low/full speed dev, highspeed hub */
 	int		ttport;		/* device port on that tt hub */
 
-	struct semaphore serialize;
-
 	unsigned int toggle[2];		/* one bit for each endpoint
 					 * ([0] = IN, [1] = OUT) */
 
···
 extern struct usb_device *usb_get_dev(struct usb_device *dev);
 extern void usb_put_dev(struct usb_device *dev);
 
-extern void usb_lock_device(struct usb_device *udev);
-extern int usb_trylock_device(struct usb_device *udev);
+/* USB device locking */
+#define usb_lock_device(udev)		down(&(udev)->dev.sem)
+#define usb_unlock_device(udev)		up(&(udev)->dev.sem)
+#define usb_trylock_device(udev)	down_trylock(&(udev)->dev.sem)
 extern int usb_lock_device_for_reset(struct usb_device *udev,
 		struct usb_interface *iface);
-extern void usb_unlock_device(struct usb_device *udev);
 
 /* USB port reset for device reinitialization */
 extern int usb_reset_device(struct usb_device *dev);