changeset 7951:c7a8bdf5af55

Changed ngx_chain_update_chains() to test tag first (ticket #2248). Without this change, aio used with HTTP/2 can result in connection hang, as observed with "aio threads; aio_write on;" and proxying (ticket #2248). The problem is that HTTP/2 updates buffers outside of the output filters (notably, marks them as sent), and then posts a write event to call output filters. If a filter does not call the next one for some reason (for example, because of an AIO operation in progress), this might result in a state when the owner of a buffer already called ngx_chain_update_chains() and can reuse the buffer, while the same buffer is still sitting in the busy chain of some other filter. In the particular case a buffer was sitting in output chain's ctx->busy, and was reused by event pipe. Output chain's ctx->busy was permanently blocked by it, and this resulted in connection hang. Fix is to change ngx_chain_update_chains() to skip buffers from other modules unconditionally, without trying to wait for these buffers to become empty.
author Maxim Dounin <mdounin@mdounin.ru>
date Sat, 30 Oct 2021 02:39:19 +0300
parents e3dbd9449b14
children 39be8a682c58
files src/core/ngx_buf.c
diffstat 1 files changed, 4 insertions(+), 4 deletions(-) [+]
line wrap: on
line diff
--- a/src/core/ngx_buf.c
+++ b/src/core/ngx_buf.c
@@ -203,16 +203,16 @@ ngx_chain_update_chains(ngx_pool_t *p, n
     while (*busy) {
         cl = *busy;
 
-        if (ngx_buf_size(cl->buf) != 0) {
-            break;
-        }
-
         if (cl->buf->tag != tag) {
             *busy = cl->next;
             ngx_free_chain(p, cl);
             continue;
         }
 
+        if (ngx_buf_size(cl->buf) != 0) {
+            break;
+        }
+
         cl->buf->pos = cl->buf->start;
         cl->buf->last = cl->buf->start;