kernel-ark/drivers/base/dd.c
Alan Stern f2eaae197f Driver core: Fix potential deadlock in driver core
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 <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2006-09-25 21:08:40 -07:00

344 lines
8.5 KiB
C

/*
* drivers/base/dd.c - The core device/driver interactions.
*
* This file contains the (sometimes tricky) code that controls the
* interactions between devices and drivers, which primarily includes
* driver binding and unbinding.
*
* All of this code used to exist in drivers/base/bus.c, but was
* relocated to here in the name of compartmentalization (since it wasn't
* strictly code just for the 'struct bus_type'.
*
* Copyright (c) 2002-5 Patrick Mochel
* Copyright (c) 2002-3 Open Source Development Labs
*
* This file is released under the GPLv2
*/
#include <linux/device.h>
#include <linux/module.h>
#include <linux/kthread.h>
#include "base.h"
#include "power/power.h"
#define to_drv(node) container_of(node, struct device_driver, kobj.entry)
/**
* device_bind_driver - bind a driver to one device.
* @dev: device.
*
* Allow manual attachment of a driver to a device.
* Caller must have already set @dev->driver.
*
* Note that this does not modify the bus reference count
* nor take the bus's rwsem. Please verify those are accounted
* for before calling this. (It is ok to call with no other effort
* from a driver's probe() method.)
*
* This function must be called with @dev->sem held.
*/
int device_bind_driver(struct device *dev)
{
int ret;
if (klist_node_attached(&dev->knode_driver)) {
printk(KERN_WARNING "%s: device %s already bound\n",
__FUNCTION__, kobject_name(&dev->kobj));
return 0;
}
pr_debug("bound device '%s' to driver '%s'\n",
dev->bus_id, dev->driver->name);
klist_add_tail(&dev->knode_driver, &dev->driver->klist_devices);
ret = sysfs_create_link(&dev->driver->kobj, &dev->kobj,
kobject_name(&dev->kobj));
if (ret == 0) {
ret = sysfs_create_link(&dev->kobj, &dev->driver->kobj,
"driver");
if (ret)
sysfs_remove_link(&dev->driver->kobj,
kobject_name(&dev->kobj));
}
return ret;
}
struct stupid_thread_structure {
struct device_driver *drv;
struct device *dev;
};
static atomic_t probe_count = ATOMIC_INIT(0);
static int really_probe(void *void_data)
{
struct stupid_thread_structure *data = void_data;
struct device_driver *drv = data->drv;
struct device *dev = data->dev;
int ret = 0;
atomic_inc(&probe_count);
pr_debug("%s: Probing driver %s with device %s\n",
drv->bus->name, drv->name, dev->bus_id);
dev->driver = drv;
if (dev->bus->probe) {
ret = dev->bus->probe(dev);
if (ret) {
dev->driver = NULL;
goto probe_failed;
}
} else if (drv->probe) {
ret = drv->probe(dev);
if (ret) {
dev->driver = NULL;
goto probe_failed;
}
}
if (device_bind_driver(dev)) {
printk(KERN_ERR "%s: device_bind_driver(%s) failed\n",
__FUNCTION__, dev->bus_id);
/* How does undo a ->probe? We're screwed. */
}
ret = 1;
pr_debug("%s: Bound Device %s to Driver %s\n",
drv->bus->name, dev->bus_id, drv->name);
goto done;
probe_failed:
if (ret == -ENODEV || ret == -ENXIO) {
/* Driver matched, but didn't support device
* or device not found.
* Not an error; keep going.
*/
ret = 0;
} else {
/* driver matched but the probe failed */
printk(KERN_WARNING
"%s: probe of %s failed with error %d\n",
drv->name, dev->bus_id, ret);
}
done:
kfree(data);
atomic_dec(&probe_count);
return ret;
}
/**
* driver_probe_done
* Determine if the probe sequence is finished or not.
*
* Should somehow figure out how to use a semaphore, not an atomic variable...
*/
int driver_probe_done(void)
{
pr_debug("%s: probe_count = %d\n", __FUNCTION__,
atomic_read(&probe_count));
if (atomic_read(&probe_count))
return -EBUSY;
return 0;
}
/**
* driver_probe_device - attempt to bind device & driver together
* @drv: driver to bind a device to
* @dev: device to try to bind to the driver
*
* First, we call the bus's match function, if one present, which should
* compare the device IDs the driver supports with the device IDs of the
* device. Note we don't do this ourselves because we don't know the
* format of the ID structures, nor what is to be considered a match and
* what is not.
*
* 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. 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)
{
struct stupid_thread_structure *data;
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;
pr_debug("%s: Matched Device %s with Driver %s\n",
drv->bus->name, dev->bus_id, drv->name);
data = kmalloc(sizeof(*data), GFP_KERNEL);
data->drv = drv;
data->dev = dev;
if (drv->multithread_probe) {
probe_task = kthread_run(really_probe, data,
"probe-%s", dev->bus_id);
if (IS_ERR(probe_task))
ret = PTR_ERR(probe_task);
} else
ret = really_probe(data);
done:
return ret;
}
static int __device_attach(struct device_driver * drv, void * data)
{
struct device * dev = data;
return driver_probe_device(drv, dev);
}
/**
* device_attach - try to attach device to a driver.
* @dev: device.
*
* Walk the list of drivers that the bus has and call
* driver_probe_device() for each pair. If a compatible
* pair is found, break out and return.
*
* 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)
{
int ret = 0;
down(&dev->sem);
if (dev->driver) {
ret = device_bind_driver(dev);
if (ret == 0)
ret = 1;
} else
ret = bus_for_each_drv(dev->bus, NULL, dev, __device_attach);
up(&dev->sem);
return ret;
}
static int __driver_attach(struct device * dev, void * data)
{
struct device_driver * drv = data;
/*
* Lock device and try to bind to it. We drop the error
* here and always return 0, because we need to keep trying
* to bind to devices and some drivers will return an error
* simply if it didn't support the device.
*
* driver_probe_device() will spit a warning if there
* 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;
}
/**
* driver_attach - try to bind driver to devices.
* @drv: driver.
*
* Walk the list of devices that the bus has on it and try to
* match the driver with each one. If driver_probe_device()
* returns 0 and the @dev->driver is set, we've found a
* compatible pair.
*/
int driver_attach(struct device_driver * drv)
{
return bus_for_each_dev(drv->bus, NULL, drv, __driver_attach);
}
/**
* device_release_driver - manually detach device from driver.
* @dev: device.
*
* 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)
{
struct device_driver * drv;
drv = dev->driver;
if (drv) {
get_driver(drv);
sysfs_remove_link(&drv->kobj, kobject_name(&dev->kobj));
sysfs_remove_link(&dev->kobj, "driver");
klist_remove(&dev->knode_driver);
if (dev->bus && dev->bus->remove)
dev->bus->remove(dev);
else if (drv->remove)
drv->remove(dev);
dev->driver = NULL;
put_driver(drv);
}
}
void device_release_driver(struct device * dev)
{
/*
* If anyone calls device_release_driver() recursively from
* within their ->remove callback for the same device, they
* will deadlock right here.
*/
down(&dev->sem);
__device_release_driver(dev);
up(&dev->sem);
}
/**
* driver_detach - detach driver from all devices it controls.
* @drv: driver.
*/
void driver_detach(struct device_driver * drv)
{
struct device * dev;
for (;;) {
spin_lock(&drv->klist_devices.k_lock);
if (list_empty(&drv->klist_devices.k_list)) {
spin_unlock(&drv->klist_devices.k_lock);
break;
}
dev = list_entry(drv->klist_devices.k_list.prev,
struct device, knode_driver.n_node);
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);
}
}
EXPORT_SYMBOL_GPL(device_bind_driver);
EXPORT_SYMBOL_GPL(device_release_driver);
EXPORT_SYMBOL_GPL(device_attach);
EXPORT_SYMBOL_GPL(driver_attach);