hash: Dropping an objcore does not rush the waiting list

Rushing the waiting list because an objcore was dropped was a source
of spurious wakeups, including the case where the dropped objcore is not
even relevant to the objhead waiting list. It is now guaranteed that an
object either dropped its OC_F_BUSY flag once ready (otherwise failed or
withdrawn) or never had this flag to begin with for objcores that can't
be looked up.

Author: dridi

bin/varnishd/cache/cache_hash.c

@@ -1107,13 +1107,13 @@ HSH_DerefObjCoreUnlock(struct worker *wrk, struct objcore **ocp, int rushmax)
 {
 	struct objcore *oc;
 	struct objhead *oh;
-	struct rush rush;
 	int r;
 
 	CHECK_OBJ_NOTNULL(wrk, WORKER_MAGIC);
 	TAKE_OBJ_NOTNULL(oc, ocp, OBJCORE_MAGIC);
 	assert(oc->refcnt > 0);
-	INIT_OBJ(&rush, RUSH_MAGIC);
+
+	(void)rushmax;
 
 	oh = oc->objhead;
 	CHECK_OBJ_NOTNULL(oh, OBJHEAD_MAGIC);
@@ -1123,15 +1123,11 @@ HSH_DerefObjCoreUnlock(struct worker *wrk, struct objcore **ocp, int rushmax)
 	r = --oc->refcnt;
 	if (!r)
 		VTAILQ_REMOVE(&oh->objcs, oc, hsh_list);
-	if (!VTAILQ_EMPTY(&oh->waitinglist)) {
-		assert(oh->refcnt > 1);
-		hsh_rush1(wrk, oh, &rush, rushmax);
-	}
 	Lck_Unlock(&oh->mtx);
-	hsh_rush2(wrk, &rush);
 	if (r != 0)
 		return (r);
 
+	AZ(oc->flags & OC_F_BUSY);
 	AZ(oc->exp_flags);
 
 	BAN_DestroyObj(oc);