From stern@rowland.harvard.edu Mon Sep 18 13:22:41 2006 Date: Mon, 18 Sep 2006 16:22:34 -0400 (EDT) From: Alan Stern To: Greg KH Subject: Driver core: Fix potential deadlock in driver core Message-ID: There is a potential deadlock in the driver core. It boils down to the fact that bus_remove_device() calls klist_remove() instead of klist_del(), thereby waiting until the reference count of the klist_node in the bus's klist of devices drops to 0. The refcount can't reach 0 so long as a modprobe process is trying to bind a new driver to the device being removed, by calling __driver_attach(). The problem is that __driver_attach() tries to acquire the device's parent's semaphore, but the caller of bus_remove_device() is quite likely to own that semaphore already. It isn't sufficient just to replace klist_remove() with klist_del(). Doing so runs the risk that the device would remain on the bus's klist of devices for some time, and so could be bound to another driver even after it was unregistered. What's needed is a new way to distinguish whether or not a device is registered, based on a criterion other than whether its klist_node is linked into the bus's klist of devices. That way driver binding can fail when the device is unregistered, even if it is still linked into the klist. This patch (as782) implements the solution, by adding a new bitflag to indiate when a struct device is registered, by testing the flag before allowing a driver to bind a device, and by changing the definition of the device_is_registered() inline. Signed-off-by: Alan Stern Signed-off-by: Greg Kroah-Hartman --- drivers/base/bus.c | 8 ++++++-- drivers/base/dd.c | 2 ++ include/linux/device.h | 3 ++- 3 files changed, 10 insertions(+), 3 deletions(-) --- gregkh-2.6.orig/drivers/base/bus.c +++ gregkh-2.6/drivers/base/bus.c @@ -392,6 +392,7 @@ out: * bus_attach_device - add device to bus * @dev: device tried to attach to a driver * + * - Add device to bus's list of devices. * - Try to attach to driver. */ int bus_attach_device(struct device * dev) @@ -400,11 +401,13 @@ int bus_attach_device(struct device * de int ret = 0; if (bus) { + dev->is_registered = 1; ret = device_attach(dev); if (ret >= 0) { klist_add_tail(&dev->knode_bus, &bus->klist_devices); ret = 0; - } + } else + dev->is_registered = 0; } return ret; } @@ -425,7 +428,8 @@ void bus_remove_device(struct device * d sysfs_remove_link(&dev->kobj, "bus"); sysfs_remove_link(&dev->bus->devices.kobj, dev->bus_id); device_remove_attrs(dev->bus, dev); - klist_remove(&dev->knode_bus); + dev->is_registered = 0; + klist_del(&dev->knode_bus); pr_debug("bus %s: remove device %s\n", dev->bus->name, dev->bus_id); device_release_driver(dev); put_bus(dev->bus); --- gregkh-2.6.orig/drivers/base/dd.c +++ gregkh-2.6/drivers/base/dd.c @@ -162,6 +162,8 @@ int driver_probe_device(struct device_dr struct task_struct *probe_task; int ret = 0; + if (!device_is_registered(dev)) + return -ENODEV; if (drv->bus->match && !drv->bus->match(dev, drv)) goto done; --- gregkh-2.6.orig/include/linux/device.h +++ gregkh-2.6/include/linux/device.h @@ -329,6 +329,7 @@ struct device { struct kobject kobj; char bus_id[BUS_ID_SIZE]; /* position on parent bus */ + unsigned is_registered:1; struct device_attribute uevent_attr; struct device_attribute *devt_attr; @@ -381,7 +382,7 @@ dev_set_drvdata (struct device *dev, voi static inline int device_is_registered(struct device *dev) { - return klist_node_attached(&dev->knode_bus); + return dev->is_registered; } /*