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
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