[nginx] Fixed premature background subrequest finalization.

[Dmitry Volyntsev]

details:   https://hg.nginx.org/nginx/rev/b4dbf8b98f9a
branches:  
changeset: 7631:b4dbf8b98f9a
user:      Dmitry Volyntsev <xeioex at nginx.com>
date:      Mon Mar 02 20:07:36 2020 +0300
description:
Fixed premature background subrequest finalization.

When "aio" or "aio threads" is used while processing the response body of an
in-memory background subrequest, the subrequest could be finalized with an aio
operation still in progress.  Upon aio completion either parent request is
woken or the old r->write_event_handler is called again.  The latter may result
in request errors.  In either case post_subrequest handler is never called with
the full response body, which is typically expected when using in-memory
subrequests.

Currently in nginx background subrequests are created by the upstream module
and the mirror module.  The issue does not manifest itself with these
subrequests because they are header-only.  But it can manifest itself with
third-party modules which create in-memory background subrequests.

diffstat:

 src/http/ngx_http_request.c |  18 +++++++++---------
 1 files changed, 9 insertions(+), 9 deletions(-)

diffs (35 lines):

diff -r f001d9384293 -r b4dbf8b98f9a src/http/ngx_http_request.c
--- a/src/http/ngx_http_request.c	Fri Feb 28 17:21:18 2020 +0300
+++ b/src/http/ngx_http_request.c	Mon Mar 02 20:07:36 2020 +0300
@@ -2490,6 +2490,15 @@ ngx_http_finalize_request(ngx_http_reque
     if (r != r->main) {
         clcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);
 
+        if (r->buffered || r->postponed) {
+
+            if (ngx_http_set_write_handler(r) != NGX_OK) {
+                ngx_http_terminate_request(r, 0);
+            }
+
+            return;
+        }
+
         if (r->background) {
             if (!r->logged) {
                 if (clcf->log_subrequest) {
@@ -2509,15 +2518,6 @@ ngx_http_finalize_request(ngx_http_reque
             return;
         }
 
-        if (r->buffered || r->postponed) {
-
-            if (ngx_http_set_write_handler(r) != NGX_OK) {
-                ngx_http_terminate_request(r, 0);
-            }
-
-            return;
-        }
-
         pr = r->parent;
 
         if (r == c->data) {