Events: improved error event handling for UDP sockets.

Normally, the epoll module calls the read and write handlers depending
on whether EPOLLIN and EPOLLOUT are reported by epoll_wait().  No error
processing is done in the module, the handlers are expected to get an
error when doing I/O.

If an error event is reported without EPOLLIN and EPOLLOUT, the module
set both EPOLLIN and EPOLLOUT to ensure the error event is handled at
least in one active handler.

This works well unless the error is delivered along with only one of
EPOLLIN or EPOLLOUT, and the corresponding handler does not do any I/O.
For example, it happened when getting EPOLLERR|EPOLLOUT from
epoll_wait() upon receiving "ICMP port unreachable" while proxying UDP.
As the write handler had nothing to send it was not able to detect and
log an error, and did not switch to the next upstream.

The fix is to unconditionally set EPOLLIN and EPOLLOUT in case of an
error event.  In the aforementioned case, this causes the read handler
to be called which does recv() and detects an error.

In addition to the epoll module, analogous changes were made in
devpoll/eventport/poll.

diff --git a/src/event/modules/ngx_devpoll_module.c b/src/event/modules/ngx_devpoll_module.c
index f985fbdfb474cde05a9bb0420cf2fc1afc458828..39e480ec8fbf08baee7ce10116d481bb63097e5d 100644 (file)
--- a/src/event/modules/ngx_devpoll_module.c
+++ b/src/event/modules/ngx_devpoll_module.c
@@ -481,13 +481,11 @@ ngx_devpoll_process_events(ngx_cycle_t *cycle, ngx_msec_t timer,
                           fd, event_list[i].events, revents);
         }
 
-        if ((revents & (POLLERR|POLLHUP|POLLNVAL))
-             && (revents & (POLLIN|POLLOUT)) == 0)
-        {
+        if (revents & (POLLERR|POLLHUP|POLLNVAL)) {
+
             /*
-             * if the error events were returned without POLLIN or POLLOUT,
-             * then add these flags to handle the events at least in one
-             * active handler
+             * if the error events were returned, add POLLIN and POLLOUT
+             * to handle the events at least in one active handler
              */
 
             revents |= POLLIN|POLLOUT;

diff --git a/src/event/modules/ngx_epoll_module.c b/src/event/modules/ngx_epoll_module.c
index c267fd6c7a83fd660ff3df0228ca77d8d5d2b191..760c69b9a0c9e751c686271c1bc3b3de1e0429c2 100644 (file)
--- a/src/event/modules/ngx_epoll_module.c
+++ b/src/event/modules/ngx_epoll_module.c
@@ -863,6 +863,13 @@ ngx_epoll_process_events(ngx_cycle_t *cycle, ngx_msec_t timer, ngx_uint_t flags)
             ngx_log_debug2(NGX_LOG_DEBUG_EVENT, cycle->log, 0,
                            "epoll_wait() error on fd:%d ev:%04XD",
                            c->fd, revents);
+
+            /*
+             * if the error events were returned, add EPOLLIN and EPOLLOUT
+             * to handle the events at least in one active handler
+             */
+
+            revents |= EPOLLIN|EPOLLOUT;
         }
 
 #if 0
@@ -873,18 +880,6 @@ ngx_epoll_process_events(ngx_cycle_t *cycle, ngx_msec_t timer, ngx_uint_t flags)
         }
 #endif
 
-        if ((revents & (EPOLLERR|EPOLLHUP))
-             && (revents & (EPOLLIN|EPOLLOUT)) == 0)
-        {
-            /*
-             * if the error events were returned without EPOLLIN or EPOLLOUT,
-             * then add these flags to handle the events at least in one
-             * active handler
-             */
-
-            revents |= EPOLLIN|EPOLLOUT;
-        }
-
         if ((revents & EPOLLIN) && rev->active) {
 
 #if (NGX_HAVE_EPOLLRDHUP)

diff --git a/src/event/modules/ngx_eventport_module.c b/src/event/modules/ngx_eventport_module.c
index dafa27f6a3a97866974672de07b193191362afd3..041359948c63ca1a184e2022333c945647794fab 100644 (file)
--- a/src/event/modules/ngx_eventport_module.c
+++ b/src/event/modules/ngx_eventport_module.c
@@ -540,13 +540,11 @@ ngx_eventport_process_events(ngx_cycle_t *cycle, ngx_msec_t timer,
                               (int) event_list[i].portev_object, revents);
             }
 
-            if ((revents & (POLLERR|POLLHUP|POLLNVAL))
-                 && (revents & (POLLIN|POLLOUT)) == 0)
-            {
+            if (revents & (POLLERR|POLLHUP|POLLNVAL)) {
+
                 /*
-                 * if the error events were returned without POLLIN or POLLOUT,
-                 * then add these flags to handle the events at least in one
-                 * active handler
+                 * if the error events were returned, add POLLIN and POLLOUT
+                 * to handle the events at least in one active handler
                  */
 
                 revents |= POLLIN|POLLOUT;

diff --git a/src/event/modules/ngx_poll_module.c b/src/event/modules/ngx_poll_module.c
index 4370950c09ecdea5242cc2181809464bd854c960..a2a7079d62794b3a61c95a8699ab6a5e1b4e55a3 100644 (file)
--- a/src/event/modules/ngx_poll_module.c
+++ b/src/event/modules/ngx_poll_module.c
@@ -353,13 +353,11 @@ ngx_poll_process_events(ngx_cycle_t *cycle, ngx_msec_t timer, ngx_uint_t flags)
             continue;
         }
 
-        if ((revents & (POLLERR|POLLHUP|POLLNVAL))
-             && (revents & (POLLIN|POLLOUT)) == 0)
-        {
+        if (revents & (POLLERR|POLLHUP|POLLNVAL)) {
+
             /*
-             * if the error events were returned without POLLIN or POLLOUT,
-             * then add these flags to handle the events at least in one
-             * active handler
+             * if the error events were returned, add POLLIN and POLLOUT
+             * to handle the events at least in one active handler
              */
 
             revents |= POLLIN|POLLOUT;