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Events: improved error event handling for UDP sockets.

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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.
This commit is contained in:
Dmitry Volyntsev 2016-11-21 16:03:42 +03:00
parent 89f92b3243
commit 433fdbf8b6
4 changed files with 19 additions and 30 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
src/event/modules/ngx_devpoll_module.c
View File

@ -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;

19
src/event/modules/ngx_epoll_module.c
View File

@ -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)

10
src/event/modules/ngx_eventport_module.c
View File

@ -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;

10
src/event/modules/ngx_poll_module.c
View File

@ -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;