changeset 7974:555533169506

HTTP/2: fixed "task already active" with sendfile in threads. With sendfile in threads, "task already active" alerts might appear in logs if a write event happens on the main HTTP/2 connection, triggering a sendfile in threads while another thread operation is already running. Observed with "aio threads; aio_write on; sendfile on;" and with thread event handlers modified to post a write event to the main HTTP/2 connection (though can happen without any modifications). Similarly, sendfile() with AIO preloading on FreeBSD can trigger duplicate aio operation, resulting in "second aio post" alerts. This is, however, harder to reproduce, especially on modern FreeBSD systems, since sendfile() usually does not return EBUSY. Fix is to avoid starting a sendfile operation if other thread operation is active by checking r->aio in the thread handler (and, similarly, in aio preload handler). The added check also makes duplicate calls protection redundant, so it is removed.
author Maxim Dounin <mdounin@mdounin.ru>
date Thu, 25 Nov 2021 22:02:05 +0300
parents 3443c02ca1d1
children a7a77549265e
files src/http/ngx_http_copy_filter_module.c src/http/ngx_http_upstream.c src/os/unix/ngx_freebsd_sendfile_chain.c src/os/unix/ngx_linux_sendfile_chain.c
diffstat 4 files changed, 58 insertions(+), 24 deletions(-) [+]
line wrap: on
line diff
--- a/src/http/ngx_http_copy_filter_module.c
+++ b/src/http/ngx_http_copy_filter_module.c
@@ -219,13 +219,25 @@ ngx_http_copy_aio_sendfile_preload(ngx_b
     ngx_http_request_t      *r;
     ngx_output_chain_ctx_t  *ctx;
 
+    aio = file->file->aio;
+    r = aio->data;
+
+    if (r->aio) {
+        /*
+         * tolerate sendfile() calls if another operation is already
+         * running; this can happen due to subrequests, multiple calls
+         * of the next body filter from a filter, or in HTTP/2 due to
+         * a write event on the main connection
+         */
+
+        return NGX_AGAIN;
+    }
+
     n = ngx_file_aio_read(file->file, buf, 1, file->file_pos, NULL);
 
     if (n == NGX_AGAIN) {
-        aio = file->file->aio;
         aio->handler = ngx_http_copy_aio_sendfile_event_handler;
 
-        r = aio->data;
         r->main->blocked++;
         r->aio = 1;
 
@@ -263,6 +275,7 @@ static ngx_int_t
 ngx_http_copy_thread_handler(ngx_thread_task_t *task, ngx_file_t *file)
 {
     ngx_str_t                  name;
+    ngx_connection_t          *c;
     ngx_thread_pool_t         *tp;
     ngx_http_request_t        *r;
     ngx_output_chain_ctx_t    *ctx;
@@ -270,6 +283,27 @@ ngx_http_copy_thread_handler(ngx_thread_
 
     r = file->thread_ctx;
 
+    if (r->aio) {
+        /*
+         * tolerate sendfile() calls if another operation is already
+         * running; this can happen due to subrequests, multiple calls
+         * of the next body filter from a filter, or in HTTP/2 due to
+         * a write event on the main connection
+         */
+
+        c = r->connection;
+
+#if (NGX_HTTP_V2)
+        if (r->stream) {
+            c = r->stream->connection->connection;
+        }
+#endif
+
+        if (task == c->sendfile_task) {
+            return NGX_OK;
+        }
+    }
+
     clcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);
     tp = clcf->thread_pool;
 
--- a/src/http/ngx_http_upstream.c
+++ b/src/http/ngx_http_upstream.c
@@ -3847,6 +3847,7 @@ ngx_http_upstream_thread_handler(ngx_thr
 {
     ngx_str_t                  name;
     ngx_event_pipe_t          *p;
+    ngx_connection_t          *c;
     ngx_thread_pool_t         *tp;
     ngx_http_request_t        *r;
     ngx_http_core_loc_conf_t  *clcf;
@@ -3854,6 +3855,27 @@ ngx_http_upstream_thread_handler(ngx_thr
     r = file->thread_ctx;
     p = r->upstream->pipe;
 
+    if (r->aio) {
+        /*
+         * tolerate sendfile() calls if another operation is already
+         * running; this can happen due to subrequests, multiple calls
+         * of the next body filter from a filter, or in HTTP/2 due to
+         * a write event on the main connection
+         */
+
+        c = r->connection;
+
+#if (NGX_HTTP_V2)
+        if (r->stream) {
+            c = r->stream->connection->connection;
+        }
+#endif
+
+        if (task == c->sendfile_task) {
+            return NGX_OK;
+        }
+    }
+
     clcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);
     tp = clcf->thread_pool;
 
--- a/src/os/unix/ngx_freebsd_sendfile_chain.c
+++ b/src/os/unix/ngx_freebsd_sendfile_chain.c
@@ -255,19 +255,6 @@ ngx_freebsd_sendfile_chain(ngx_connectio
 #if (NGX_HAVE_AIO_SENDFILE)
 
         if (ebusy) {
-            if (aio->event.active) {
-                /*
-                 * tolerate duplicate calls; they can happen due to subrequests
-                 * or multiple calls of the next body filter from a filter
-                 */
-
-                if (sent) {
-                    c->busy_count = 0;
-                }
-
-                return in;
-            }
-
             if (sent == 0) {
                 c->busy_count++;
 
--- a/src/os/unix/ngx_linux_sendfile_chain.c
+++ b/src/os/unix/ngx_linux_sendfile_chain.c
@@ -379,15 +379,6 @@ ngx_linux_sendfile_thread(ngx_connection
         return ctx->sent;
     }
 
-    if (task->event.active && ctx->file == file) {
-        /*
-         * tolerate duplicate calls; they can happen due to subrequests
-         * or multiple calls of the next body filter from a filter
-         */
-
-        return NGX_DONE;
-    }
-
     ctx->file = file;
     ctx->socket = c->fd;
     ctx->size = size;