res_pjsip: Deny requests when threadpool queue is backed up.

We have observed situations where the SIP threadpool may become
deadlocked. However, because incoming traffic is still arriving, the SIP
threadpool's queue can continue to grow, eventually running the system
out of memory.

This change makes it so that incoming traffic gets rejected with a 503
response if the queue is backed up too much.

Change-Id: I4e736d48a2ba79fd1f8056c0dcd330e38e6a3816

include/asterisk/res_pjsip.h

@@ -2104,4 +2104,10 @@ int ast_sip_get_host_ip(int af, pj_sockaddr *addr);
  */
 const char *ast_sip_get_host_ip_string(int af);
 
+/*!
+ * \brief Return the size of the SIP threadpool's task queue
+ * \since 13.7.0
+ */
+long ast_sip_threadpool_queue_size(void);
+
 #endif /* _RES_PJSIP_H */

include/asterisk/taskprocessor.h

@@ -262,4 +262,10 @@ int ast_taskprocessor_is_task(struct ast_taskprocessor *tps);
  */
 const char *ast_taskprocessor_name(struct ast_taskprocessor *tps);
 
+/*!
+ * \brief Return the current size of the taskprocessor queue
+ * \since 13.7.0
+ */
+long ast_taskprocessor_size(struct ast_taskprocessor *tps);
+
 #endif /* __AST_TASKPROCESSOR_H__ */

include/asterisk/threadpool.h

@@ -292,4 +292,10 @@ struct ast_taskprocessor *ast_threadpool_serializer(const char *name, struct ast
 struct ast_taskprocessor *ast_threadpool_serializer_group(const char *name,
 	struct ast_threadpool *pool, struct ast_serializer_shutdown_group *shutdown_group);
 
+/*!
+ * \brief Return the size of the threadpool's task queue
+ * \since 13.7.0
+ */
+long ast_threadpool_queue_size(struct ast_threadpool *pool);
+
 #endif /* ASTERISK_THREADPOOL_H */

main/taskprocessor.c

@@ -130,9 +130,6 @@ static int tps_ping_handler(void *datap);
 /*! \brief Remove the front task off the taskprocessor queue */
 static struct tps_task *tps_taskprocessor_pop(struct ast_taskprocessor *tps);
 
-/*! \brief Return the size of the taskprocessor queue */
-static int tps_taskprocessor_depth(struct ast_taskprocessor *tps);
-
 static char *cli_tps_ping(struct ast_cli_entry *e, int cmd, struct ast_cli_args *a);
 static char *cli_tps_report(struct ast_cli_entry *e, int cmd, struct ast_cli_args *a);
 
@@ -508,7 +505,7 @@ static struct tps_task *tps_taskprocessor_pop(struct ast_taskprocessor *tps)
 	return task;
 }
 
-static int tps_taskprocessor_depth(struct ast_taskprocessor *tps)
+long ast_taskprocessor_size(struct ast_taskprocessor *tps)
 {
 	return (tps) ? tps->tps_queue_size : -1;
 }
@@ -765,7 +762,7 @@ int ast_taskprocessor_execute(struct ast_taskprocessor *tps)
 {
 	struct ast_taskprocessor_local local;
 	struct tps_task *t;
-	int size;
+	long size;
 
 	ao2_lock(tps);
 	t = tps_taskprocessor_pop(tps);
@@ -797,7 +794,7 @@ int ast_taskprocessor_execute(struct ast_taskprocessor *tps)
 	 * after we pop an empty stack.
 	 */
 	tps->executing = 0;
-	size = tps_taskprocessor_depth(tps);
+	size = ast_taskprocessor_size(tps);
 	/* If we executed a task, bump the stats */
 	if (tps->stats) {
 		tps->stats->_tasks_processed_count++;

main/threadpool.c

@@ -1397,3 +1397,8 @@ struct ast_taskprocessor *ast_threadpool_serializer(const char *name, struct ast
 {
 	return ast_threadpool_serializer_group(name, pool, NULL);
 }
+
+long ast_threadpool_queue_size(struct ast_threadpool *pool)
+{
+	return ast_taskprocessor_size(pool->tps);
+}

res/res_pjsip.c

@@ -3809,6 +3809,11 @@ static void remove_request_headers(pjsip_endpoint *endpt)
 	}
 }
 
+long ast_sip_threadpool_queue_size(void)
+{
+	return ast_threadpool_queue_size(sip_threadpool);
+}
+
 AST_TEST_DEFINE(xml_sanitization_end_null)
 {
 	char sanitized[8];

res/res_pjsip/pjsip_distributor.c

@@ -246,6 +246,8 @@ static pjsip_module endpoint_mod = {
 	.on_rx_request = endpoint_lookup,
 };
 
+#define SIP_MAX_QUEUE 500L
+
 static pj_bool_t distributor(pjsip_rx_data *rdata)
 {
 	pjsip_dialog *dlg = find_dialog(rdata);
@@ -280,7 +282,17 @@ static pj_bool_t distributor(pjsip_rx_data *rdata)
 		clone->endpt_info.mod_data[endpoint_mod.id] = ao2_bump(dist->endpoint);
 	}
 
-	ast_sip_push_task(serializer, distribute, clone);
+	if (ast_sip_threadpool_queue_size() > SIP_MAX_QUEUE) {
+		/* When the threadpool is backed up this much, there is a good chance that we have encountered
+		 * some sort of terrible condition and don't need to be adding more work to the threadpool.
+		 * It's in our best interest to send back a 503 response and be done with it.
+		 */
+		pjsip_endpt_respond_stateless(ast_sip_get_pjsip_endpoint(), rdata, 503, NULL, NULL, NULL);
+		ao2_cleanup(clone->endpt_info.mod_data[endpoint_mod.id]);
+		pjsip_rx_data_free_cloned(clone);
+	} else {
+		ast_sip_push_task(serializer, distribute, clone);
+	}
 
 end:
 	if (dlg) {