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changeset 7975:a7a77549265e

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HTTP/2: fixed sendfile() aio handling. With sendfile() in threads ("aio threads; sendfile on;"), client connection can block on writing, waiting for sendfile() to complete. In HTTP/2 this might result in the request hang, since an attempt to continue processing in thread event handler will call request's write event handler, which is usually stopped by ngx_http_v2_send_chain(): it does nothing if there are no additional data and stream->queued is set. Further, HTTP/2 resets stream's c->write->ready to 0 if writing blocks, so just fixing ngx_http_v2_send_chain() is not enough. Can be reproduced with test suite on Linux with: TEST_NGINX_GLOBALS_HTTP="aio threads; sendfile on;" prove h2*.t The following tests currently fail: h2_keepalive.t, h2_priority.t, h2_proxy_max_temp_file_size.t, h2.t, h2_trailers.t. Similarly, sendfile() with AIO preloading on FreeBSD can block as well, with similar results. This is, however, harder to reproduce, especially on modern FreeBSD systems, since sendfile() usually does not return EBUSY. Fix is to modify ngx_http_v2_send_chain() so it actually tries to send data to the main connection when called, and to make sure that c->write->ready is set by the relevant event handlers.
author Maxim Dounin <mdounin@mdounin.ru>
date Thu, 25 Nov 2021 22:02:10 +0300
parents 555533169506
children 76aea0ad78e5
files src/http/ngx_http_copy_filter_module.c src/http/ngx_http_upstream.c src/http/v2/ngx_http_v2_filter_module.c
diffstat 3 files changed, 65 insertions(+), 10 deletions(-) [+]
line wrap: on
line diff
--- a/src/http/ngx_http_copy_filter_module.c
+++ b/src/http/ngx_http_copy_filter_module.c
@@ -253,16 +253,32 @@ static void
 ngx_http_copy_aio_sendfile_event_handler(ngx_event_t *ev)
 {
     ngx_event_aio_t     *aio;
+    ngx_connection_t    *c;
     ngx_http_request_t  *r;
 
     aio = ev->data;
     r = aio->data;
+    c = r->connection;
 
     r->main->blocked--;
     r->aio = 0;
     ev->complete = 0;
 
-    r->connection->write->handler(r->connection->write);
+#if (NGX_HTTP_V2)
+
+    if (r->stream) {
+        /*
+         * for HTTP/2, update write event to make sure processing will
+         * reach the main connection to handle sendfile() preload
+         */
+
+        c->write->ready = 1;
+        c->write->active = 0;
+    }
+
+#endif
+
+    c->write->handler(c->write);
 }
 
 #endif
@@ -357,6 +373,20 @@ ngx_http_copy_thread_event_handler(ngx_e
     r->main->blocked--;
     r->aio = 0;
 
+#if (NGX_HTTP_V2)
+
+    if (r->stream) {
+        /*
+         * for HTTP/2, update write event to make sure processing will
+         * reach the main connection to handle sendfile() in threads
+         */
+
+        c->write->ready = 1;
+        c->write->active = 0;
+    }
+
+#endif
+
     if (r->done) {
         /*
          * trigger connection event handler if the subrequest was
--- a/src/http/ngx_http_upstream.c
+++ b/src/http/ngx_http_upstream.c
@@ -3927,6 +3927,20 @@ ngx_http_upstream_thread_event_handler(n
     r->main->blocked--;
     r->aio = 0;
 
+#if (NGX_HTTP_V2)
+
+    if (r->stream) {
+        /*
+         * for HTTP/2, update write event to make sure processing will
+         * reach the main connection to handle sendfile() in threads
+         */
+
+        c->write->ready = 1;
+        c->write->active = 0;
+    }
+
+#endif
+
     if (r->done) {
         /*
          * trigger connection event handler if the subrequest was
--- a/src/http/v2/ngx_http_v2_filter_module.c
+++ b/src/http/v2/ngx_http_v2_filter_module.c
@@ -1432,6 +1432,9 @@ ngx_http_v2_send_chain(ngx_connection_t 
     size = 0;
 #endif
 
+    ngx_log_debug1(NGX_LOG_DEBUG_HTTP, fc->log, 0,
+                   "http2 send chain: %p", in);
+
     while (in) {
         size = ngx_buf_size(in->buf);
 
@@ -1450,12 +1453,8 @@ ngx_http_v2_send_chain(ngx_connection_t 
             return NGX_CHAIN_ERROR;
         }
 
-        if (stream->queued) {
-            fc->write->active = 1;
-            fc->write->ready = 0;
-
-        } else {
-            fc->buffered &= ~NGX_HTTP_V2_BUFFERED;
+        if (ngx_http_v2_filter_send(fc, stream) == NGX_ERROR) {
+            return NGX_CHAIN_ERROR;
         }
 
         return NULL;
@@ -1464,9 +1463,16 @@ ngx_http_v2_send_chain(ngx_connection_t 
     h2c = stream->connection;
 
     if (size && ngx_http_v2_flow_control(h2c, stream) == NGX_DECLINED) {
-        fc->write->active = 1;
-        fc->write->ready = 0;
-        return in;
+
+        if (ngx_http_v2_filter_send(fc, stream) == NGX_ERROR) {
+            return NGX_CHAIN_ERROR;
+        }
+
+        if (ngx_http_v2_flow_control(h2c, stream) == NGX_DECLINED) {
+            fc->write->active = 1;
+            fc->write->ready = 0;
+            return in;
+        }
     }
 
     if (in->buf->tag == (ngx_buf_tag_t) &ngx_http_v2_filter_get_shadow) {
@@ -1809,6 +1815,11 @@ ngx_http_v2_waiting_queue(ngx_http_v2_co
 static ngx_inline ngx_int_t
 ngx_http_v2_filter_send(ngx_connection_t *fc, ngx_http_v2_stream_t *stream)
 {
+    if (stream->queued == 0) {
+        fc->buffered &= ~NGX_HTTP_V2_BUFFERED;
+        return NGX_OK;
+    }
+
     stream->blocked = 1;
 
     if (ngx_http_v2_send_output_queue(stream->connection) == NGX_ERROR) {