From bf74ad5bc41727d5f2f1c6bedb2c1fac394de731 Mon Sep 17 00:00:00 2001 From: Alan Stern Date: Thu, 17 Nov 2005 16:54:12 -0500 Subject: [PATCH] [PATCH] Hold the device's parent's lock during probe and remove This patch (as604) makes the driver core hold a device's parent's lock as well as the device's lock during calls to the probe and remove methods in a driver. This facility is needed by USB device drivers, owing to the peculiar way USB devices work: A device provides multiple interfaces, and drivers are bound to interfaces rather than to devices; Nevertheless a reset, reset-configuration, suspend, or resume affects the entire device and requires the caller to hold the lock for the device, not just a lock for one of the interfaces. Since a USB driver's probe method is always called with the interface lock held, the locking order rules (always lock parent before child) prevent these methods from acquiring the device lock. The solution provided here is to call all probe and remove methods, for all devices (not just USB), with the parent lock already acquired. Although currently only the USB subsystem requires these changes, people have mentioned in prior discussion that the overhead of acquiring an extra semaphore in all the prove/remove sequences is not overly large. Up to now, the USB core has been using its own set of private semaphores. A followup patch will remove them, relying entirely on the device semaphores provided by the driver core. The code paths affected by this patch are: device_add and device_del: The USB core already holds the parent lock, so no actual change is needed. driver_register and driver_unregister: The driver core will now lock both the parent and the device before probing or removing. driver_bind and driver_unbind (in sysfs): These routines will now lock both the parent and the device before binding or unbinding. bus_rescan_devices: The helper routine will lock the parent before probing a device. I have not tested this patch for conflicts with other subsystems. As far as I can see, the only possibility of conflict would lie in the bus_rescan_devices pathway, and it seems pretty remote. Nevertheless, it would be good for this to get a lot of testing in -mm. Signed-off-by: Alan Stern Signed-off-by: Greg Kroah-Hartman --- drivers/base/bus.c | 15 ++++++++++++++- drivers/base/dd.c | 15 ++++++++++++++- 2 files changed, 28 insertions(+), 2 deletions(-) diff --git a/drivers/base/bus.c b/drivers/base/bus.c index fa601b085e..e3f915a248 100644 --- a/drivers/base/bus.c +++ b/drivers/base/bus.c @@ -152,7 +152,11 @@ static ssize_t driver_unbind(struct device_driver *drv, dev = bus_find_device(bus, NULL, (void *)buf, driver_helper); if (dev && dev->driver == drv) { + if (dev->parent) /* Needed for USB */ + down(&dev->parent->sem); device_release_driver(dev); + if (dev->parent) + up(&dev->parent->sem); err = count; } put_device(dev); @@ -175,9 +179,13 @@ static ssize_t driver_bind(struct device_driver *drv, dev = bus_find_device(bus, NULL, (void *)buf, driver_helper); if (dev && dev->driver == NULL) { + if (dev->parent) /* Needed for USB */ + down(&dev->parent->sem); down(&dev->sem); err = driver_probe_device(drv, dev); up(&dev->sem); + if (dev->parent) + up(&dev->parent->sem); } put_device(dev); put_bus(bus); @@ -484,8 +492,13 @@ void bus_remove_driver(struct device_driver * drv) /* Helper for bus_rescan_devices's iter */ static int bus_rescan_devices_helper(struct device *dev, void *data) { - if (!dev->driver) + if (!dev->driver) { + if (dev->parent) /* Needed for USB */ + down(&dev->parent->sem); device_attach(dev); + if (dev->parent) + up(&dev->parent->sem); + } return 0; } diff --git a/drivers/base/dd.c b/drivers/base/dd.c index 3b419c9a1e..2b90501666 100644 --- a/drivers/base/dd.c +++ b/drivers/base/dd.c @@ -65,7 +65,8 @@ void device_bind_driver(struct device * dev) * This function returns 1 if a match is found, an error if one * occurs (that is not -ENODEV or -ENXIO), and 0 otherwise. * - * This function must be called with @dev->sem held. + * This function must be called with @dev->sem held. When called + * for a USB interface, @dev->parent->sem must be held as well. */ int driver_probe_device(struct device_driver * drv, struct device * dev) { @@ -123,6 +124,8 @@ static int __device_attach(struct device_driver * drv, void * data) * * Returns 1 if the device was bound to a driver; * 0 if no matching device was found; error code otherwise. + * + * When called for a USB interface, @dev->parent->sem must be held. */ int device_attach(struct device * dev) { @@ -152,10 +155,14 @@ static int __driver_attach(struct device * dev, void * data) * is an error. */ + if (dev->parent) /* Needed for USB */ + down(&dev->parent->sem); down(&dev->sem); if (!dev->driver) driver_probe_device(drv, dev); up(&dev->sem); + if (dev->parent) + up(&dev->parent->sem); return 0; } @@ -181,6 +188,8 @@ void driver_attach(struct device_driver * drv) * Manually detach device from driver. * * __device_release_driver() must be called with @dev->sem held. + * When called for a USB interface, @dev->parent->sem must be held + * as well. */ static void __device_release_driver(struct device * dev) @@ -233,10 +242,14 @@ void driver_detach(struct device_driver * drv) get_device(dev); spin_unlock(&drv->klist_devices.k_lock); + if (dev->parent) /* Needed for USB */ + down(&dev->parent->sem); down(&dev->sem); if (dev->driver == drv) __device_release_driver(dev); up(&dev->sem); + if (dev->parent) + up(&dev->parent->sem); put_device(dev); } } -- 2.39.5