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

[Francis Deslauriers]

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).
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