Forgot to pass the struct wrk* argument to the task function.

bin/varnishd/cache/cache.h

@@ -288,7 +288,7 @@ struct wrk_accept {
 
 /* Worker pool stuff -------------------------------------------------*/
 
-typedef void pool_func_t(struct pool *pp, void *priv);
+typedef void pool_func_t(struct pool *pp, struct worker *wrk, void *priv);
 
 struct pool_task {
 	VTAILQ_ENTRY(pool_task)		list;

bin/varnishd/cache/cache_pool.c

@@ -257,7 +257,7 @@ Pool_Work_Thread(void *priv, struct worker *wrk)
 
 		if (tp != NULL) {
 			Lck_Unlock(&pp->mtx);
-			tp->func(pp, tp->priv);
+			tp->func(pp, wrk, tp->priv);
 			stats_clean = WRK_TrySumStat(wrk);
 			Lck_Lock(&pp->mtx);
 			continue;