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>
diff --git a/drivers/firewire/fw-device.c b/drivers/firewire/fw-device.c
index de9066e..c04c288 100644
--- a/drivers/firewire/fw-device.c
+++ b/drivers/firewire/fw-device.c
@@ -610,12 +610,14 @@
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 @@
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 @@
}
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 @@
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)