Re: Question about (or bug in?) the kobject implementation

[Alan Stern]

On Wed, 3 Mar 2004, Greg KH wrote:

> On Fri, Feb 27, 2004 at 11:02:34PM -0500, Alan Stern wrote:
> > We're actually discussing two different questions here.
> > 
> >     A.	Is it okay to call kobject_add() after calling kobject_del() -- 
> > 	this was my original question.
> 
> No, this is not ok.  It might happen to work, but it is not valid.

I want to understand _why_ it is not valid.  Can you explain please?

>From what you said earlier, I got the impression that calling _add() after 
_del() is illegal because it runs the risk that the refcount may be 0 and 
the object may be gone.  But if you have a separate valid reference, that 
can't happen.  Would it be legal then, or is there more to it?


> >     B.	Can we prevent people from doing kobject_get() after the kobject's
> > 	refcount has dropped to 0?
> 
> By saying, "you can not call kobject_get() on a object that you know is
> released with kobject_del()".  If you already have a valid reference,
> you can always call kobject_get().  But once you call kobject_del() that
> pointer you passed should not be passed to kobject_get() as it may now
> be gone.
> 
> Does that help?
> 
> thanks,
> 
> greg k-h

Alan Stern

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