diff options
author | Alan Stern <stern@rowland.harvard.edu> | 2005-11-17 17:10:32 -0500 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@suse.de> | 2006-01-04 13:48:34 -0800 |
commit | 9ad3d6ccf5eee285e233dbaf186369b8d477a666 (patch) | |
tree | 4ad43518e01f1b2c6513e79b318d974979041b99 /drivers/usb/core/usb.c | |
parent | 75318d2d7cab77b14c5d3dbd5e69f2680a769e16 (diff) | |
download | op-kernel-dev-9ad3d6ccf5eee285e233dbaf186369b8d477a666.zip op-kernel-dev-9ad3d6ccf5eee285e233dbaf186369b8d477a666.tar.gz |
[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>
Diffstat (limited to 'drivers/usb/core/usb.c')
-rw-r--r-- | drivers/usb/core/usb.c | 114 |
1 files changed, 9 insertions, 105 deletions
diff --git a/drivers/usb/core/usb.c b/drivers/usb/core/usb.c index 294e9f1..fcfda21 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); |