[lttng-dev] [PATCH lttng-modules] Fix: atomic_add_unless() returns true/false rather than prior value

[Mathieu Desnoyers]

----- On Mar 8, 2017, at 11:38 AM, Francis Deslauriers francis.deslauriers at efficios.com wrote:

> The previous implementation assumed that `atomic_add_unless` returned the
> prior value of the atomic counter when in fact it returned if addition was
> successful(true) or overflowed(false).

I think you mean "if addition was performed (true) or not performed (false)" ?

Thanks,

Mathieu

> Since `atomic_add_unless` can not return INT_MAX, the `lttng_kref_get`
> always returned that the call was successful.
> 
> This issue had a low likelihood of being triggered since the two refcounts
> of the counters used with this call are both bounded by the maximum
> number of file descriptors on the system.
> 
> Signed-off-by: Francis Deslauriers <francis.deslauriers at efficios.com>
> ---
> wrapper/kref.h | 6 +-----
> 1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/wrapper/kref.h b/wrapper/kref.h
> index eedefbf..f30a9ae 100644
> --- a/wrapper/kref.h
> +++ b/wrapper/kref.h
> @@ -36,11 +36,7 @@
>  */
> static inline int lttng_kref_get(struct kref *kref)
> {
> -	if (atomic_add_unless(&kref->refcount, 1, INT_MAX) != INT_MAX) {
> -		return 1;
> -	} else {
> -		return 0;
> -	}
> +	return atomic_add_unless(&kref->refcount, 1, INT_MAX);
> }
> 
> #endif /* _LTTNG_WRAPPER_KREF_H */
> --
> 2.7.4

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com