[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 <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

7 files changed, 32 insertions, 148 deletions

diff --git a/drivers/usb/core/devices.c b/drivers/usb/core/devices.c
index 83e815d3cd52..55bc563a3256 100644
--- a/drivers/usb/core/devices.c
+++ b/drivers/usb/core/devices.c
@@ -545,10 +545,10 @@ static ssize_t usb_device_dump(char __user **buffer, size_t *nbytes, loff_t *ski
                 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;
diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
index 3a73170e95dd..2b68998fe4b3 100644
--- a/drivers/usb/core/devio.c
+++ b/drivers/usb/core/devio.c
@@ -1349,9 +1349,7 @@ static int proc_ioctl(struct dev_state *ps, struct usbdevfs_ioctl *ctl)
         /* 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;
 
diff --git a/drivers/usb/core/driver.c b/drivers/usb/core/driver.c
index bb139f06bcd6..076462c8ba2a 100644
--- a/drivers/usb/core/driver.c
+++ b/drivers/usb/core/driver.c
@@ -432,9 +432,7 @@ int usb_register_driver(struct usb_driver *new_driver, struct module *owner)
         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",
@@ -465,11 +463,9 @@ void usb_deregister(struct usb_driver *driver)
 {
         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();
 }
diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
index da24c31ee00d..d16a0e8a7d72 100644
--- a/drivers/usb/core/hcd.c
+++ b/drivers/usb/core/hcd.c
@@ -857,9 +857,7 @@ static int register_root_hub (struct usb_device *usb_dev,
                 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",
@@ -1891,7 +1889,10 @@ void usb_remove_hcd(struct usb_hcd *hcd)
         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);
diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 40c6c50c6bd9..dd3bcfb2bcb6 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -32,7 +32,7 @@
 #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);
 
@@ -975,8 +975,8 @@ static int locktree(struct usb_device *udev)
                         /* 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;
                 }
         }
@@ -1132,16 +1132,10 @@ void usb_disconnect(struct usb_device **pdev)
          * 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++) {
                 if (udev->children[i])
@@ -1169,11 +1163,7 @@ void usb_disconnect(struct usb_device **pdev)
         *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);
 }
@@ -1243,8 +1233,8 @@ static inline void show_string(struct usb_device *udev, char *id, char *string)
  *
  * 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.
@@ -1254,8 +1244,7 @@ static inline void show_string(struct usb_device *udev, char *id, char *string)
  *
  * 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)
 {
@@ -1364,6 +1353,8 @@ 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.
          */
@@ -1385,6 +1376,8 @@ int usb_new_device(struct usb_device *udev)
         /* USB device state == configured ... usable */
         usb_notify_add_device(udev);
 
+        usb_unlock_device(udev);
+
         return 0;
 
 fail:
@@ -1872,11 +1865,8 @@ int usb_resume_device(struct usb_device *udev)
         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;
 }
 
@@ -1889,14 +1879,14 @@ static int remote_wakeup(struct usb_device *udev)
         /* 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;
 }
@@ -1997,7 +1987,7 @@ static int hub_resume(struct usb_interface *intf)
 
                 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 {
@@ -2008,7 +1998,7 @@ static int hub_resume(struct usb_interface *intf)
                                 hub_port_logical_disconnect(hub, port1);
                         }
                 }
-                up(&udev->serialize);
+                usb_unlock_device(udev);
         }
         }
 #endif
@@ -2573,7 +2563,6 @@ static void hub_port_connect_change(struct usb_hub *hub, int port1,
                  * 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
@@ -2597,7 +2586,6 @@ static void hub_port_connect_change(struct usb_hub *hub, int port1,
                         }
                 }
 
-                up (&udev->serialize);
                 if (status)
                         goto loop_disable;
 
diff --git a/drivers/usb/core/usb.c b/drivers/usb/core/usb.c
index 294e9f127477..fcfda21be499 100644
--- a/drivers/usb/core/usb.c
+++ b/drivers/usb/core/usb.c
@@ -32,7 +32,6 @@
 #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>
@@ -49,8 +48,6 @@ const char *usbcore_name = "usbcore";
 static int nousb;       /* Disable USB when built into kernel image */
                         /* Not honored on modular build */
 
-static DECLARE_RWSEM(usb_all_devices_rwsem);
-
 
 /**
  * usb_ifnum_to_if - get the interface object with a given interface number
@@ -446,8 +443,6 @@ usb_alloc_dev(struct usb_device *parent, struct usb_bus *bus, unsigned port1)
         dev->parent = parent;
         INIT_LIST_HEAD(&dev->filelist);
 
-        init_MUTEX(&dev->serialize);
-
         return dev;
 }
 
@@ -520,76 +515,21 @@ void usb_put_intf(struct usb_interface *intf)
 
 /*                      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
  *      usb device structure
  * @udev: device that's being locked
@@ -627,7 +567,7 @@ int usb_lock_device_for_reset(struct usb_device *udev,
                 }
         }
 
-        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 */
@@ -645,39 +585,6 @@ int usb_lock_device_for_reset(struct usb_device *udev,
         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);
-}
-
 
 static struct usb_device *match_device(struct usb_device *dev,
                                        u16 vendor_id, u16 product_id)
@@ -700,10 +607,10 @@ static struct usb_device *match_device(struct usb_device *dev,
         /* 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;
                 }
@@ -1300,10 +1207,7 @@ EXPORT_SYMBOL(usb_put_dev);
 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);
diff --git a/drivers/usb/core/usb.h b/drivers/usb/core/usb.h
index 98e85fb4d3b7..4647e1ebc68d 100644
--- a/drivers/usb/core/usb.h
+++ b/drivers/usb/core/usb.h
@@ -16,9 +16,6 @@ extern int usb_get_device_descriptor(struct usb_device *dev,
 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);