Fixed runtime handling of systems without EPOLLRDHUP support.

In 7583:efd71d49bde0 (nginx 1.17.5) along with introduction of the
ioctl(FIONREAD) support proper handling of systems without EPOLLRDHUP
support in the kernel (but with EPOLLRDHUP in headers) was broken.

Before the change, rev->available was never set to 0 unless
ngx_use_epoll_rdhup was also set (that is, runtime test for EPOLLRDHUP
introduced in 6536:f7849bfb6d21 succeeded).  After the change,
rev->available might reach 0 on systems without runtime EPOLLRDHUP
support, stopping further reading in ngx_readv_chain() and ngx_unix_recv().
And, if EOF happened to be already reported along with the last event,
it is not reported again by epoll_wait(), leading to connection hangs
and timeouts on such systems.

This affects Linux kernels before 2.6.17 if nginx was compiled
with newer headers, and, more importantly, emulation layers, such as
DigitalOcean's App Platform's / gVisor's epoll emulation layer.

Fix is to explicitly check ngx_use_epoll_rdhup before the corresponding
rev->pending_eof tests in ngx_readv_chain() and ngx_unix_recv().

diff --git a/src/os/unix/ngx_readv_chain.c b/src/os/unix/ngx_readv_chain.c
index b1ae4b51d2e40a342ca6223fb1d004838f515530..370a4011f88f8be8246284c236991425efb453d0 100644 (file)
--- a/src/os/unix/ngx_readv_chain.c
+++ b/src/os/unix/ngx_readv_chain.c
@@ -55,7 +55,9 @@ ngx_readv_chain(ngx_connection_t *c, ngx_chain_t *chain, off_t limit)
 
 #if (NGX_HAVE_EPOLLRDHUP)
 
-    if (ngx_event_flags & NGX_USE_EPOLL_EVENT) {
+    if ((ngx_event_flags & NGX_USE_EPOLL_EVENT)
+        && ngx_use_epoll_rdhup)
+    {
         ngx_log_debug2(NGX_LOG_DEBUG_EVENT, c->log, 0,
                        "readv: eof:%d, avail:%d",
                        rev->pending_eof, rev->available);

diff --git a/src/os/unix/ngx_recv.c b/src/os/unix/ngx_recv.c
index ddfae4dbee66069043bb7149d6686889a3b2ef1e..cc04a5fbb10430675997626fdde88eded1c7da4d 100644 (file)
--- a/src/os/unix/ngx_recv.c
+++ b/src/os/unix/ngx_recv.c
@@ -52,7 +52,9 @@ ngx_unix_recv(ngx_connection_t *c, u_char *buf, size_t size)
 
 #if (NGX_HAVE_EPOLLRDHUP)
 
-    if (ngx_event_flags & NGX_USE_EPOLL_EVENT) {
+    if ((ngx_event_flags & NGX_USE_EPOLL_EVENT)
+        && ngx_use_epoll_rdhup)
+    {
         ngx_log_debug2(NGX_LOG_DEBUG_EVENT, c->log, 0,
                        "recv: eof:%d, avail:%d",
                        rev->pending_eof, rev->available);