Greg and Pat:
This patch (as536) simplifies the driver-model core by replacing the klist
used to store the set of devices bound to a driver with a regular list
protected by a mutex. It turns out that even with a klist, there are too
many opportunities for races for the list to be used safely by more than
one thread at a time. And given that only one thread uses the list at any
moment, there's no need to add all the extra overhead of making it a
klist.
This version of the patch addresses the concerns raised earlier by Pat:
the list and mutex have been given more succinct names, and the obscure
special-case code in device_attach has been replaced with a FIXME comment.
Note that the new iterators in driver.c could easily be changed to use
list_for_each_entry_safe and list_for_each_entry, if the functions didn't
offer the feature of starting in the middle of the list. If no callers
use that feature, it should be removed.
I still think the APIs for device_bind_driver and device_release_driver
need to be changed, because they each rely on dev->drv not changing at a
time when no protecting locks are held. They will have to be fixed up in
a later patch.
Alan Stern
Signed-off-by: Alan Stern <[email protected]>
Index: usb-2.6/drivers/base/dd.c
===================================================================
--- usb-2.6.orig/drivers/base/dd.c
+++ usb-2.6/drivers/base/dd.c
@@ -24,28 +24,37 @@
#define to_drv(node) container_of(node, struct device_driver, kobj.entry)
+/*
+ * The caller must hold both @dev->drv->devlist_mutex and
+ * @dev->sem (acquired in that order).
+ */
+static void __device_bind_driver(struct device * dev)
+{
+ pr_debug("bound device '%s' to driver '%s'\n",
+ dev->bus_id, dev->driver->name);
+ list_add_tail(&dev->node_driver, &dev->driver->devlist);
+ sysfs_create_link(&dev->driver->kobj, &dev->kobj,
+ kobject_name(&dev->kobj));
+ sysfs_create_link(&dev->kobj, &dev->driver->kobj, "driver");
+}
+
/**
* 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.
*/
void device_bind_driver(struct device * dev)
{
- pr_debug("bound device '%s' to driver '%s'\n",
- dev->bus_id, dev->driver->name);
- klist_add_tail(&dev->driver->klist_devices, &dev->knode_driver);
- sysfs_create_link(&dev->driver->kobj, &dev->kobj,
- kobject_name(&dev->kobj));
- sysfs_create_link(&dev->kobj, &dev->driver->kobj, "driver");
+ struct device_driver *drv = dev->driver;
+
+ down(&drv->devlist_mutex);
+ down(&dev->sem);
+ if (dev->driver == drv)
+ __device_bind_driver(dev);
+ up(&dev->sem);
+ up(&drv->devlist_mutex);
}
/**
@@ -59,16 +68,21 @@ void device_bind_driver(struct device *
* 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.
+ * The caller must hold @drv->devlist_mutex.
*/
int driver_probe_device(struct device_driver * drv, struct device * dev)
{
int ret = 0;
+ down(&dev->sem);
+ if (dev->driver) {
+ ret = -EBUSY;
+ goto Done;
+ }
+
if (drv->bus->match && !drv->bus->match(dev, drv))
goto Done;
@@ -82,7 +96,7 @@ int driver_probe_device(struct device_dr
goto ProbeFailed;
}
}
- device_bind_driver(dev);
+ __device_bind_driver(dev);
ret = 1;
pr_debug("%s: Bound Device %s to Driver %s\n",
drv->bus->name, dev->bus_id, drv->name);
@@ -102,13 +116,20 @@ int driver_probe_device(struct device_dr
drv->name, dev->bus_id, ret);
}
Done:
+ up(&dev->sem);
return ret;
}
static int __device_attach(struct device_driver * drv, void * data)
{
struct device * dev = data;
- return driver_probe_device(drv, dev);
+ int ret;
+
+ down(&drv->devlist_mutex);
+ ret = driver_probe_device(drv, dev);
+ up(&drv->devlist_mutex);
+
+ return ret;
}
/**
@@ -124,15 +145,21 @@ static int __device_attach(struct device
*/
int device_attach(struct device * dev)
{
- int ret = 0;
+ int ret = 1;
+ struct device_driver * drv;
- down(&dev->sem);
- if (dev->driver) {
- device_bind_driver(dev);
- ret = 1;
+ drv = dev->driver;
+ if (drv) {
+
+ /* FIXME: What if drv is rmmod'ed right now? */
+
+ down(&drv->devlist_mutex);
+ down(&dev->sem);
+ __device_bind_driver(dev);
+ up(&dev->sem);
+ up(&drv->devlist_mutex);
} else
ret = bus_for_each_drv(dev->bus, NULL, dev, __device_attach);
- up(&dev->sem);
return ret;
}
@@ -141,7 +168,7 @@ static int __driver_attach(struct device
struct device_driver * drv = data;
/*
- * Lock device and try to bind to it. We drop the error
+ * Try to bind drv to dev. 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.
@@ -150,11 +177,8 @@ static int __driver_attach(struct device
* is an error.
*/
- down(&dev->sem);
if (!dev->driver)
driver_probe_device(drv, dev);
- up(&dev->sem);
-
return 0;
}
@@ -170,46 +194,55 @@ static int __driver_attach(struct device
*/
void driver_attach(struct device_driver * drv)
{
+ down(&drv->devlist_mutex);
bus_for_each_dev(drv->bus, NULL, drv, __driver_attach);
+ up(&drv->devlist_mutex);
}
-/**
- * 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.
- */
-static void __device_release_driver(struct device * dev)
+/*
+ * The caller must hold @driver->devlist_mutex.
+ */
+static int __device_release_driver(struct device * dev, void * driver)
{
- struct device_driver * drv;
+ struct device_driver * drv = driver;
- drv = dev->driver;
- if (drv) {
- get_driver(drv);
+ down(&dev->sem);
+ if (dev->driver == drv) {
sysfs_remove_link(&drv->kobj, kobject_name(&dev->kobj));
sysfs_remove_link(&dev->kobj, "driver");
- klist_remove(&dev->knode_driver);
+ list_del(&dev->node_driver);
if (drv->remove)
drv->remove(dev);
dev->driver = NULL;
- put_driver(drv);
}
+ up(&dev->sem);
+ return 0;
}
+/**
+ * device_release_driver - manually detach device from driver.
+ * @dev: device.
+ *
+ * Manually detach device from driver.
+ */
void device_release_driver(struct device * dev)
{
+ struct device_driver * drv;
+
+ drv = dev->driver;
+ if (!drv)
+ return;
+
/*
* 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);
+ down(&drv->devlist_mutex);
+ __device_release_driver(dev, drv);
+ up(&drv->devlist_mutex);
}
@@ -219,25 +252,7 @@ void device_release_driver(struct device
*/
void driver_detach(struct device_driver * drv)
{
- struct device * dev;
-
- for (;;) {
- spin_lock_irq(&drv->klist_devices.k_lock);
- if (list_empty(&drv->klist_devices.k_list)) {
- spin_unlock_irq(&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_irq(&drv->klist_devices.k_lock);
-
- down(&dev->sem);
- if (dev->driver == drv)
- __device_release_driver(dev);
- up(&dev->sem);
- put_device(dev);
- }
+ driver_for_each_device(drv, NULL, drv, __device_release_driver);
}
Index: usb-2.6/drivers/base/driver.c
===================================================================
--- usb-2.6.orig/drivers/base/driver.c
+++ usb-2.6/drivers/base/driver.c
@@ -15,16 +15,10 @@
#include <linux/string.h>
#include "base.h"
-#define to_dev(node) container_of(node, struct device, driver_list)
+#define to_dev(node) container_of(node, struct device, node_driver)
#define to_drv(obj) container_of(obj, struct device_driver, kobj)
-static struct device * next_device(struct klist_iter * i)
-{
- struct klist_node * n = klist_next(i);
- return n ? container_of(n, struct device, knode_driver) : NULL;
-}
-
/**
* driver_for_each_device - Iterator for devices bound to a driver.
* @drv: Driver we're iterating.
@@ -37,18 +31,22 @@ static struct device * next_device(struc
int driver_for_each_device(struct device_driver * drv, struct device * start,
void * data, int (*fn)(struct device *, void *))
{
- struct klist_iter i;
- struct device * dev;
+ struct list_head * ptr, * tmp;
int error = 0;
if (!drv)
return -EINVAL;
- klist_iter_init_node(&drv->klist_devices, &i,
- start ? &start->knode_driver : NULL);
- while ((dev = next_device(&i)) && !error)
- error = fn(dev, data);
- klist_iter_exit(&i);
+ down(&drv->devlist_mutex);
+ ptr = (start ? &start->node_driver : drv->devlist.next);
+ while (ptr != &drv->devlist) {
+ tmp = ptr->next;
+ error = fn(to_dev(ptr), data);
+ if (error)
+ break;
+ ptr = tmp;
+ }
+ up(&drv->devlist_mutex);
return error;
}
@@ -74,18 +72,22 @@ struct device * driver_find_device(struc
struct device * start, void * data,
int (*match)(struct device *, void *))
{
- struct klist_iter i;
- struct device *dev;
+ struct list_head * ptr;
+ struct device *dev = NULL;
if (!drv)
return NULL;
- klist_iter_init_node(&drv->klist_devices, &i,
- (start ? &start->knode_driver : NULL));
- while ((dev = next_device(&i)))
+ down(&drv->devlist_mutex);
+ ptr = (start ? &start->node_driver : drv->devlist.next);
+ for (; ptr != &drv->devlist; ptr = ptr->next) {
+ dev = to_dev(ptr);
if (match(dev, data) && get_device(dev))
break;
- klist_iter_exit(&i);
+ }
+ if (ptr == &drv->devlist)
+ dev = NULL;
+ up(&drv->devlist_mutex);
return dev;
}
EXPORT_SYMBOL_GPL(driver_find_device);
@@ -157,7 +159,8 @@ void put_driver(struct device_driver * d
*/
int driver_register(struct device_driver * drv)
{
- klist_init(&drv->klist_devices);
+ INIT_LIST_HEAD(&drv->devlist);
+ init_MUTEX(&drv->devlist_mutex);
init_completion(&drv->unloaded);
return bus_add_driver(drv);
}
Index: usb-2.6/include/linux/device.h
===================================================================
--- usb-2.6.orig/include/linux/device.h
+++ usb-2.6/include/linux/device.h
@@ -107,7 +107,8 @@ struct device_driver {
struct completion unloaded;
struct kobject kobj;
- struct klist klist_devices;
+ struct list_head devlist;
+ struct semaphore devlist_mutex;
struct klist_node knode_bus;
struct module * owner;
@@ -270,7 +271,7 @@ extern void class_device_destroy(struct
struct device {
struct klist klist_children;
struct klist_node knode_parent; /* node in sibling list */
- struct klist_node knode_driver;
+ struct list_head node_driver;
struct klist_node knode_bus;
struct device * parent;
Index: usb-2.6/drivers/base/bus.c
===================================================================
--- usb-2.6.orig/drivers/base/bus.c
+++ usb-2.6/drivers/base/bus.c
@@ -133,7 +133,7 @@ static struct kobj_type ktype_bus = {
decl_subsys(bus, &ktype_bus, NULL);
-/* Manually detach a device from it's associated driver. */
+/* Manually detach a device from its associated driver. */
static int driver_helper(struct device *dev, void *data)
{
const char *name = data;
@@ -175,9 +175,9 @@ static ssize_t driver_bind(struct device
dev = bus_find_device(bus, NULL, (void *)buf, driver_helper);
if ((dev) &&
(dev->driver == NULL)) {
- down(&dev->sem);
+ down(&drv->devlist_mutex);
err = driver_probe_device(drv, dev);
- up(&dev->sem);
+ up(&drv->devlist_mutex);
put_device(dev);
}
return err;
-
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