improve busyobj panic

For backend requests, we do not have the thread local storage of the
client thread available, so trq.req will normally be (nil).

Dump the busyobj back pointers to req/sess/wrk to maximize the
usefulness of panics.

Also reorder the panic by struct busyobj and add some more members
which may or may not be useful (but when we find out, it is likely
too late).

Also move the vmod list dump to the top level.

Noticed when trying to understand if #2667 was also a stack overflow
in the context of #2817

bin/varnishd/cache/cache_panic.c

@@ -60,6 +60,7 @@ static struct vsb pan_vsb_storage, *pan_vsb;
 static pthread_mutex_t panicstr_mtx;
 
 static void pan_sess(struct vsb *, const struct sess *);
+static void pan_req(struct vsb *, const struct req *);
 
 /*--------------------------------------------------------------------*/
 
@@ -399,8 +400,39 @@ pan_busyobj(struct vsb *vsb, const struct busyobj *bo)
 		return;
 	VSB_indent(vsb, 2);
 	PAN_CheckMagic(vsb, bo, BUSYOBJ_MAGIC);
+	VSB_printf(vsb, "end = %p,\n", bo->end);
+	VSB_printf(vsb, "retries = %d,\n", bo->retries);
+
+	if (bo->req != NULL)
+		pan_req(vsb, bo->req);
+	if (bo->sp != NULL)
+		pan_sess(vsb, bo->sp);
+	if (bo->wrk != NULL)
+		pan_wrk(vsb, bo->wrk);
+
+	if (bo->vfc != NULL)
+		pan_vfp(vsb, bo->vfc);
+	if (bo->filter_list != NULL)
+		VSB_printf(vsb, "filter_list = \"%s\",\n", bo->filter_list);
+
 	pan_ws(vsb, bo->ws);
-	VSB_printf(vsb, "retries = %d, ", bo->retries);
+	VSB_printf(vsb, "ws_bo = %p,\n", (void *)bo->ws_bo);
+
+	// bereq0 left out
+	if (bo->bereq != NULL && bo->bereq->ws != NULL)
+		pan_http(vsb, "bereq", bo->bereq);
+	if (bo->beresp != NULL && bo->beresp->ws != NULL)
+		pan_http(vsb, "beresp", bo->beresp);
+	if (bo->stale_oc)
+		pan_objcore(vsb, "stale_oc", bo->stale_oc);
+	if (bo->fetch_objcore)
+		pan_objcore(vsb, "fetch", bo->fetch_objcore);
+
+	if (VALID_OBJ(bo->htc, HTTP_CONN_MAGIC))
+		pan_htc(vsb, bo->htc);
+
+	// fetch_task left out
+
 	VSB_printf(vsb, "flags = {");
 	p = "";
 /*lint -save -esym(438,p) -e539 */
@@ -410,27 +442,14 @@ pan_busyobj(struct vsb *vsb, const struct busyobj *bo)
 /*lint -restore */
 	VSB_printf(vsb, "},\n");
 
-	if (VALID_OBJ(bo->htc, HTTP_CONN_MAGIC))
-		pan_htc(vsb, bo->htc);
-
-	if (bo->vfc)
-		pan_vfp(vsb, bo->vfc);
+	// timeouts/timers/acct/storage left out
 
 	VDI_Panic(bo->director_req, vsb, "director_req");
 	if (bo->director_resp == bo->director_req)
 		VSB_printf(vsb, "director_resp = director_req,\n");
 	else
 		VDI_Panic(bo->director_resp, vsb, "director_resp");
-	if (bo->bereq != NULL && bo->bereq->ws != NULL)
-		pan_http(vsb, "bereq", bo->bereq);
-	if (bo->beresp != NULL && bo->beresp->ws != NULL)
-		pan_http(vsb, "beresp", bo->beresp);
-	if (bo->fetch_objcore)
-		pan_objcore(vsb, "fetch", bo->fetch_objcore);
-	if (bo->stale_oc)
-		pan_objcore(vsb, "ims", bo->stale_oc);
 	VCL_Panic(vsb, bo->vcl);
-	VMOD_Panic(vsb);
 	VSB_indent(vsb, -2);
 	VSB_printf(vsb, "},\n");
 }
@@ -495,7 +514,6 @@ pan_req(struct vsb *vsb, const struct req *req)
 		pan_http(vsb, "resp", req->resp);
 
 	VCL_Panic(vsb, req->vcl);
-	VMOD_Panic(vsb);
 
 	if (req->body_oc != NULL)
 		pan_objcore(vsb, "BODY", req->body_oc);
@@ -683,6 +701,7 @@ pan_ic(const char *func, const char *file, int line, const char *cond,
 		pan_busyobj(pan_vsb, bo);
 		if (bo != NULL)
 			VSL_Flush(bo->vsl, 0);
+		VMOD_Panic(pan_vsb);
 	} else {
 		VSB_printf(pan_vsb,
 		    "Feature short panic supressed details.\n");