Improved ngx_http_subrequest() error handling.

Previously, request might be left in inconsistent state in case of error,
which manifested in "http request count is zero" alerts when used by SSI
filter.

The fix is to reshuffle initialization order to postpone committing state
changes until after any potentially failing parts.

Found by bad memory allocator simulation.

diff --git a/src/http/ngx_http_core_module.c b/src/http/ngx_http_core_module.c
index a1540c01858381375d97d5dac8b3c964ef8543a5..92c3eae8a153ae016412e829d7debb447223e3f1 100644 (file)
--- a/src/http/ngx_http_core_module.c
+++ b/src/http/ngx_http_core_module.c
@@ -2327,6 +2327,7 @@ ngx_http_subrequest(ngx_http_request_t *r,
     ngx_connection_t              *c;
     ngx_http_request_t            *sr;
     ngx_http_core_srv_conf_t      *cscf;
+    ngx_http_posted_request_t     *posted;
     ngx_http_postponed_request_t  *pr, *p;
 
     if (r->subrequests == 0) {
@@ -2380,6 +2381,11 @@ ngx_http_subrequest(ngx_http_request_t *r,
         return NGX_ERROR;
     }
 
+    posted = ngx_palloc(r->pool, sizeof(ngx_http_posted_request_t));
+    if (posted == NULL) {
+        return NGX_ERROR;
+    }
+
     cscf = ngx_http_get_module_srv_conf(r, ngx_http_core_module);
     sr->main_conf = cscf->ctx->main_conf;
     sr->srv_conf = cscf->ctx->srv_conf;
@@ -2438,10 +2444,6 @@ ngx_http_subrequest(ngx_http_request_t *r,
     }
 
     if (!sr->background) {
-        if (c->data == r && r->postponed == NULL) {
-            c->data = sr;
-        }
-
         pr = ngx_palloc(r->pool, sizeof(ngx_http_postponed_request_t));
         if (pr == NULL) {
             return NGX_ERROR;
@@ -2451,6 +2453,10 @@ ngx_http_subrequest(ngx_http_request_t *r,
         pr->out = NULL;
         pr->next = NULL;
 
+        if (c->data == r && r->postponed == NULL) {
+            c->data = sr;
+        }
+
         if (r->postponed) {
             for (p = r->postponed; p->next; p = p->next) { /* void */ }
             p->next = pr;
@@ -2498,7 +2504,7 @@ ngx_http_subrequest(ngx_http_request_t *r,
         ngx_http_update_location_config(sr);
     }
 
-    return ngx_http_post_request(sr, NULL);
+    return ngx_http_post_request(sr, posted);
 }