In file src/event/ngx_event_timer.c:
function:
void ngx_event_expire_timers (void)
{
.... ...
for ( ;; ) {

[color=#FF0000]ngx_mutex_lock(ngx_event_timer_mutex);[/color]

root = ngx_event_timer_rbtree.root;

[color=#FF0000]if (root == sentinel) {
return;
}[/color]
... ...
}

While timer rb-tree is empty, mutex_lock 'ngx_event_timer_mutex' would not unlock!

This bug is avaliable in every nginx version. Should fix it pls.