[4.1] 12b384b Improve output on PRIV_TASK/TOP in init/fini.

[Lasse Karstensen]

commit 12b384ba0a23bcaa6767bf6804db96cb61cfa71f
Author: Lasse Karstensen <lkarsten at varnish-software.com>
Date:   Thu May 26 12:51:38 2016 +0200

    Improve output on PRIV_TASK/TOP in init/fini.
    
    Output a proper error message instead of a more cryptic assert
    if the vmod writer does the wrong thing.
    
    Ref: #1811

diff --git a/bin/varnishd/cache/cache_vrt_priv.c b/bin/varnishd/cache/cache_vrt_priv.c
index c499312..fd8215b 100644
--- a/bin/varnishd/cache/cache_vrt_priv.c
+++ b/bin/varnishd/cache/cache_vrt_priv.c
@@ -115,10 +115,11 @@ VRT_priv_task(VRT_CTX, void *vmod_id)
 	if (ctx->req) {
 		CHECK_OBJ_NOTNULL(ctx->req, REQ_MAGIC);
 		id = (uintptr_t)ctx->req;
-	} else {
+	} else if (ctx->bo) {
 		CHECK_OBJ_NOTNULL(ctx->bo, BUSYOBJ_MAGIC);
 		id = (uintptr_t)ctx->bo;
-	}
+	} else
+		WRONG("PRIV_TASK is only accessible in client or backend VCL contexts");
 	return (VRT_priv_dynamic(ctx, id, (uintptr_t)vmod_id));
 }
 
@@ -133,7 +134,8 @@ VRT_priv_top(VRT_CTX, void *vmod_id)
 		CHECK_OBJ_NOTNULL(ctx->req->top, REQ_MAGIC);
 		id = (uintptr_t)&ctx->req->top->top;
 		return (VRT_priv_dynamic(ctx, id, (uintptr_t)vmod_id));
-	}
+	} else
+		WRONG("PRIV_TOP is only accessible in client VCL context");
 	return (NULL);
 }