DNS: Need to use the same serializer for a pjproject SIP transaction.

All send/receive processing for a SIP transaction needs to be done under
the same threadpool serializer to prevent reentrancy problems inside
pjproject when using an external DNS resolver to process messages for the
transaction.

* Add threadpool API call to get the current serializer associated with
the worker thread.

* Pick a serializer from a pool of default serializers if the caller of
res_pjsip.c:ast_sip_push_task() does not provide one.

This is a simple way to ensure that all outgoing SIP request messages are
processed under a serializer.  Otherwise, any place where a pushed task is
done that would result in an outgoing out-of-dialog request would need to
be modified to supply a serializer.  Serializers from the default
serializer pool are picked in a round robin sequence for simplicity.

A side effect is that the default serializer pool will limit the growth of
the thread pool from random tasks.  This is not necessarily a bad thing.

* Made pjsip_resolver.c use the requesting thread's serializer to execute
the async callback.

* Made pjsip_distributor.c save the thread's serializer name on the
outgoing request tdata struct so the response can be processed under the
same serializer.

ASTERISK-25115 #close
Reported by: John Bigelow

Change-Id: Iea71c16ce1132017b5791635e198b8c27973f40a

res/res_pjsip/pjsip_distributor.c

@@ -22,22 +22,106 @@
 
 #include "asterisk/res_pjsip.h"
 #include "include/res_pjsip_private.h"
+#include "asterisk/taskprocessor.h"
+#include "asterisk/threadpool.h"
 
 static int distribute(void *data);
 static pj_bool_t distributor(pjsip_rx_data *rdata);
+static pj_status_t record_serializer(pjsip_tx_data *tdata);
 
 static pjsip_module distributor_mod = {
 	.name = {"Request Distributor", 19},
 	.priority = PJSIP_MOD_PRIORITY_TSX_LAYER - 6,
+	.on_tx_request = record_serializer,
 	.on_rx_request = distributor,
 	.on_rx_response = distributor,
 };
 
+/*!
+ * \internal
+ * \brief Record the task's serializer name on the tdata structure.
+ * \since 14.0.0
+ *
+ * \param tdata The outgoing message.
+ *
+ * \retval PJ_SUCCESS.
+ */
+static pj_status_t record_serializer(pjsip_tx_data *tdata)
+{
+	struct ast_taskprocessor *serializer;
+
+	serializer = ast_threadpool_serializer_get_current();
+	if (serializer) {
+		const char *name;
+
+		name = ast_taskprocessor_name(serializer);
+		if (!ast_strlen_zero(name)
+			&& (!tdata->mod_data[distributor_mod.id]
+				|| strcmp(tdata->mod_data[distributor_mod.id], name))) {
+			char *tdata_name;
+
+			/* The serializer in use changed. */
+			tdata_name = pj_pool_alloc(tdata->pool, strlen(name) + 1);
+			strcpy(tdata_name, name);/* Safe */
+
+			tdata->mod_data[distributor_mod.id] = tdata_name;
+		}
+	}
+
+	return PJ_SUCCESS;
+}
+
+/*!
+ * \internal
+ * \brief Find the request tdata to get the serializer it used.
+ * \since 14.0.0
+ *
+ * \param rdata The incoming message.
+ *
+ * \retval serializer on success.
+ * \retval NULL on error or could not find the serializer.
+ */
+static struct ast_taskprocessor *find_request_serializer(pjsip_rx_data *rdata)
+{
+	struct ast_taskprocessor *serializer = NULL;
+	pj_str_t tsx_key;
+	pjsip_transaction *tsx;
+
+	pjsip_tsx_create_key(rdata->tp_info.pool, &tsx_key, PJSIP_ROLE_UAC,
+		&rdata->msg_info.cseq->method, rdata);
+
+	tsx = pjsip_tsx_layer_find_tsx(&tsx_key, PJ_TRUE);
+	if (!tsx) {
+		ast_debug(1, "Could not find %.*s transaction for %d response.\n",
+			(int) pj_strlen(&rdata->msg_info.cseq->method.name),
+			pj_strbuf(&rdata->msg_info.cseq->method.name),
+			rdata->msg_info.msg->line.status.code);
+		return NULL;
+	}
+
+	if (tsx->last_tx) {
+		const char *serializer_name;
+
+		serializer_name = tsx->last_tx->mod_data[distributor_mod.id];
+		if (!ast_strlen_zero(serializer_name)) {
+			serializer = ast_taskprocessor_get(serializer_name, TPS_REF_IF_EXISTS);
+		}
+	}
+
+#ifdef HAVE_PJ_TRANSACTION_GRP_LOCK
+	pj_grp_lock_release(tsx->grp_lock);
+#else
+	pj_mutex_unlock(tsx->mutex);
+#endif
+
+	return serializer;
+}
+
 /*! Dialog-specific information the distributor uses */
 struct distributor_dialog_data {
-	/* Serializer to distribute tasks to for this dialog */
+	/*! Serializer to distribute tasks to for this dialog */
 	struct ast_taskprocessor *serializer;
-	/* Endpoint associated with this dialog */
+	/*! Endpoint associated with this dialog */
 	struct ast_sip_endpoint *endpoint;
 };
 
@@ -167,6 +251,7 @@ static pj_bool_t distributor(pjsip_rx_data *rdata)
 	pjsip_dialog *dlg = find_dialog(rdata);
 	struct distributor_dialog_data *dist = NULL;
 	struct ast_taskprocessor *serializer = NULL;
+	struct ast_taskprocessor *req_serializer = NULL;
 	pjsip_rx_data *clone;
 
 	if (dlg) {
@@ -176,11 +261,16 @@ static pj_bool_t distributor(pjsip_rx_data *rdata)
 		}
 	}
 
-	if (rdata->msg_info.msg->type == PJSIP_REQUEST_MSG && (
-		!pjsip_method_cmp(&rdata->msg_info.msg->line.req.method, &pjsip_cancel_method) || 
-		!pjsip_method_cmp(&rdata->msg_info.msg->line.req.method, &pjsip_bye_method)) &&
-		!serializer) {
-		pjsip_endpt_respond_stateless(ast_sip_get_pjsip_endpoint(), rdata, 481, NULL, NULL, NULL);
+	if (serializer) {
+		/* We have a serializer so we know where to send the message. */
+	} else if (rdata->msg_info.msg->type == PJSIP_RESPONSE_MSG) {
+		req_serializer = find_request_serializer(rdata);
+		serializer = req_serializer;
+	} else if (!pjsip_method_cmp(&rdata->msg_info.msg->line.req.method, &pjsip_cancel_method)
+		|| !pjsip_method_cmp(&rdata->msg_info.msg->line.req.method, &pjsip_bye_method)) {
+		/* We have a BYE or CANCEL request without a serializer. */
+		pjsip_endpt_respond_stateless(ast_sip_get_pjsip_endpoint(), rdata,
+			PJSIP_SC_CALL_TSX_DOES_NOT_EXIST, NULL, NULL, NULL);
 		goto end;
 	}
 
@@ -196,6 +286,7 @@ end:
 	if (dlg) {
 		pjsip_dlg_dec_lock(dlg);
 	}
+	ast_taskprocessor_unreference(req_serializer);
 
 	return PJ_TRUE;
 }