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>

1 files changed, 5 insertions, 3 deletions

diff --git a/drivers/firewire/fw-cdev.c b/drivers/firewire/fw-cdev.c
index 7e73cbaa4121..44ccee26c368 100644
--- a/drivers/firewire/fw-cdev.c
+++ b/drivers/firewire/fw-cdev.c
@@ -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);