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

[Greg KH <greg@kroah.com>]

On Mon, Apr 24, 2006 at 04:33:34PM +0800, Akinobu Mita wrote:
> This patch adds warning to detect kref_put() with unreferenced kref.
> 
> Signed-off-by: Akinobu Mita <mita@miraclelinux.com>
> 
>  lib/kref.c |   14 ++++++++------
>  1 files changed, 8 insertions(+), 6 deletions(-)
> 
> Index: 2.6-git/lib/kref.c
> ===================================================================
> --- 2.6-git.orig/lib/kref.c
> +++ 2.6-git/lib/kref.c
> @@ -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.

> @@ -56,12 +57,13 @@ int kref_put(struct kref *kref, void (*r
>  	 * if current count is one, we are the last user and can release object
>  	 * right now, avoiding an atomic operation on 'refcount'
>  	 */
> -	if ((atomic_read(&kref->refcount) == 1) ||
> -	    (atomic_dec_and_test(&kref->refcount))) {
> -		release(kref);
> -		return 1;
> -	}
> -	return 0;
> +	if (atomic_read(&kref->refcount) == 1)
> +		atomic_set(&kref->refcount, 0);
> +	else if (!atomic_dec_and_test(&kref->refcount))
> +		return 0;
> +
> +	release(kref);
> +	return 1;

What does this change do?  What are you trying to help out with?
CONFIG_DEBUG_SLAB will check to see if you reference krefs that have
already been freed.

thanks,

greg k -h