fellow_cache: Fix fellow_cache_obj_slim reference count for waiting

src/fellow_cache.c

@@ -3522,14 +3522,14 @@ fellow_cache_obj_slim(const struct fellow_cache *fc,
 
 			// NULL: can not be on lru
 			(void) fellow_cache_seg_ref_locked(NULL, fcs);
-			ref = 1;
+			ref++;
 			fellow_cache_seg_wait_locked(fcs);
 
 			AZ(pthread_mutex_lock(&lru->lru_mtx));
 		}
 		if (fcs->state == FCS_INCORE &&
-		    ref == 1 && fcs->refcnt == ref) {
-			/* we hold the only ref, can not be on LRU,
+		    ref > 0 && fcs->refcnt == ref) {
+			/* we own all refs, can not be on LRU,
 			 * so no need to go through full deref
 			 */
 			fcs->refcnt = 0;
@@ -3547,7 +3547,7 @@ fellow_cache_obj_slim(const struct fellow_cache *fc,
 
 		AZ(fcs->fcs_onlru);
 		if (ref)
-			(void) fellow_cache_seg_deref_locked(NULL, fcs);
+			(void) fellow_cache_seg_deref_n_locked(NULL, fcs, ref);
 	}
 	AZ(pthread_mutex_unlock(&lru->lru_mtx));