Messages in this thread | | | Date | Fri, 4 Dec 2009 17:07:11 -0500 (EST) | From | Alan Stern <> | Subject | Re: [PATCH] Driver core: fix race in dev_driver_string |
| |
On Fri, 4 Dec 2009, Oliver Neukum wrote:
> OK, yes. It's a bad example. However this is tricky. > > This is a bug then: > > mutex_lock(...); > > if (instance->error) { > rv = instance->error; > instance->error = 0; > dev_dbg(instance->dev,...);
Unless you can guarantee at this point that instance->dev isn't stale, it is indeed a bug.
> goto err_out; > } > > rv = -ENODEV; > if (instance->disconnected) > goto err_out; > > > One approach is to set instance->dev to NULL in disconnect(). That > > wouldn't do much good for your dev_dbg(), though. A better solution is > > to refcount the instance->dev pointer: Take a reference to the device > > when setting instance->dev and drop it when clearing instance->dev (or > > when instance is freed). > > That would mean that I am forced to adopt refcounting just to print > something. This seems very inelegant.
What can I say? When the something you want to print can be deallocated at any time, there isn't much choice.
Maybe reference counting is inelegant; it depends on your point of view. Can you think of a more elegant way to make sure that a pointer isn't stale?
Alan Stern
| |