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firewire: fix "kobject_add failed for fw* with -EEXIST" 

There is a race between shutdown and creation of devices:  fw-core may
attempt to add a device with the same name of an already existing
device.  http://bugzilla.kernel.org/show_bug.cgi?id=9828

Impact of the bug:  Happens rarely (when shutdown of a device coincides
with creation of another), forces the user to unplug and replug the new
device to get it working.

The fix is obvious:  Free the minor number *after* instead of *before*
device_unregister().  This requires to take an additional reference of
the fw_device as long as the IDR tree points to it.

And while we are at it, we fix an additional race condition:
fw_device_op_open() took its reference of the fw_device a little bit too
late, hence was in danger to access an already invalid fw_device.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
This commit is contained in:
Stefan Richter 2008-02-02 15:01:09 +01:00
parent 1b9c12ba2f
commit 96b19062e7
3 changed files with 20 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
drivers/firewire/fw-cdev.c
View File

@ -109,15 +109,17 @@ static int fw_device_op_open(struct inode *inode, struct file *file)
struct client *client;
unsigned long flags;
device = fw_device_from_devt(inode->i_rdev);
device = fw_device_get_by_devt(inode->i_rdev);
if (device == NULL)
return -ENODEV;
client = kzalloc(sizeof(*client), GFP_KERNEL);
if (client == NULL)
if (client == NULL) {
fw_device_put(device);
return -ENOMEM;
}
client->device = fw_device_get(device);
client->device = device;
INIT_LIST_HEAD(&client->event_list);
INIT_LIST_HEAD(&client->resource_list);
spin_lock_init(&client->lock);

20
drivers/firewire/fw-device.c
View File

@ -610,12 +610,14 @@ static DECLARE_RWSEM(idr_rwsem);
static DEFINE_IDR(fw_device_idr);
int fw_cdev_major;
struct fw_device *fw_device_from_devt(dev_t devt)
struct fw_device *fw_device_get_by_devt(dev_t devt)
{
struct fw_device *device;
down_read(&idr_rwsem);
device = idr_find(&fw_device_idr, MINOR(devt));
if (device)
fw_device_get(device);
up_read(&idr_rwsem);
return device;
@ -627,13 +629,14 @@ static void fw_device_shutdown(struct work_struct *work)
container_of(work, struct fw_device, work.work);
int minor = MINOR(device->device.devt);
down_write(&idr_rwsem);
idr_remove(&fw_device_idr, minor);
up_write(&idr_rwsem);
fw_device_cdev_remove(device);
device_for_each_child(&device->device, NULL, shutdown_unit);
device_unregister(&device->device);
down_write(&idr_rwsem);
idr_remove(&fw_device_idr, minor);
up_write(&idr_rwsem);
fw_device_put(device);
}
static struct device_type fw_device_type = {
@ -682,10 +685,13 @@ static void fw_device_init(struct work_struct *work)
}
err = -ENOMEM;
fw_device_get(device);
down_write(&idr_rwsem);
if (idr_pre_get(&fw_device_idr, GFP_KERNEL))
err = idr_get_new(&fw_device_idr, device, &minor);
up_write(&idr_rwsem);
if (err < 0)
goto error;
@ -741,7 +747,9 @@ static void fw_device_init(struct work_struct *work)
idr_remove(&fw_device_idr, minor);
up_write(&idr_rwsem);
error:
put_device(&device->device);
fw_device_put(device); /* fw_device_idr's reference */
put_device(&device->device); /* our reference */
}
static int update_unit(struct device *dev, void *data)

2
drivers/firewire/fw-device.h
View File

@ -77,13 +77,13 @@ fw_device_is_shutdown(struct fw_device *device)
}
struct fw_device *fw_device_get(struct fw_device *device);
struct fw_device *fw_device_get_by_devt(dev_t devt);
void fw_device_put(struct fw_device *device);
int fw_device_enable_phys_dma(struct fw_device *device);
void fw_device_cdev_update(struct fw_device *device);
void fw_device_cdev_remove(struct fw_device *device);
struct fw_device *fw_device_from_devt(dev_t devt);
extern int fw_cdev_major;
struct fw_unit {