Re: [patch 1/4] kref: warn kref_put() with unreferenced kref

[Akinobu Mita <mita@miraclelinux.com>]

On Mon, Apr 24, 2006 at 08:51:28PM -0700, Greg KH wrote:
> > @@ -49,6 +49,7 @@ void kref_get(struct kref *kref)
> >   */
> >  int kref_put(struct kref *kref, void (*release)(struct kref *kref))
> >  {
> > +	WARN_ON(atomic_read(&kref->refcount) < 1);
> 
> How can this ever be true?  If the refcount _ever_ goes below 1, the
> object is freed.

The idea of detection kref_put() with unreferenced object was stolen
from BUG_ON()es in blocks/ll_rw_blk.c and fs/bio.c

ll_rw_blk.c:    BUG_ON(atomic_read(&ioc->refcount) == 0);

bio.c:          BIO_BUG_ON(!atomic_read(&bio->bi_cnt));

But the kref counter usually does not become zero. Because kref is
trying to reduce the number of atomic_dec_and_test()

So this patch also set kref counter to zero here:

> > +	if (atomic_read(&kref->refcount) == 1)
> > +		atomic_set(&kref->refcount, 0);