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Fixed req_app_link reference counting on cancellation.

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Re-scheduled req_app_link structures should have use_count exactly equal
to the number of references from the application and port list.  However,
there's one extra usage decrement that occurs after the req_app_link is
created because the use_count is initialised as 1.

This patch removes all excess instances of the usage decrement that caused
preliminary req_app_link release and router process crash.

To reproduce the issue need to cause request rescheduling between 2 app
processes.

This issue was introduced in 61e9f23a566d.
This commit is contained in:
Max Romanov
2020-02-03 11:20:59 +03:00
parent 8c0f2cebf5
commit 7ea9ebc55a
1 changed files with 7 additions and 16 deletions
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23
src/nxt_router.c
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@@ -3750,8 +3750,6 @@ nxt_router_response_error_handler(nxt_task_t *task, nxt_port_recv_msg_t *msg,
nxt_router_app_prepare_request(task, req_app_link);
}
nxt_request_app_link_use(task, req_app_link, -1);
msg->port_msg.last = 0;
return;
@@ -4220,28 +4218,23 @@ re_ra_cancelled:
if (nxt_router_port_post_select(task, &state) == NXT_OK) {
/*
* There should be call nxt_request_app_link_inc_use(re_ra),
* but we need to decrement use then. So, let's skip both.
* because of one more link in the queue.
* Corresponding decrement is in nxt_router_app_process_request().
*/
nxt_request_app_link_inc_use(re_ra);
nxt_work_queue_add(&task->thread->engine->fast_work_queue,
nxt_router_app_process_request,
&task->thread->engine->task, app, re_ra);
} else {
/*
* This call should be unconditional, but we want to spare
* couple of CPU ticks to postpone the head death of the universe.
*/
nxt_request_app_link_use(task, re_ra, -1);
}
}
if (req_app_link != NULL) {
/*
* Here we do the same trick as described above,
* but without conditions.
* Skip required nxt_request_app_link_inc_use(req_app_link).
* There should be call nxt_request_app_link_inc_use(req_app_link),
* because of one more link in the queue. But one link was
* recently removed from app->requests link.
*/
nxt_work_queue_add(&task->thread->engine->fast_work_queue,
@@ -5205,8 +5198,6 @@ nxt_router_app_timeout(nxt_task_t *task, void *obj, void *data)
if (nxt_router_port_post_select(task, &state) == NXT_OK) {
nxt_router_app_prepare_request(task, pending_ra);
}
nxt_request_app_link_use(task, pending_ra, -1);
}
nxt_debug(task, "send quit to app '%V' pid %PI", &app->name, port->pid);