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

include/asterisk/threadpool.h

@@ -195,6 +195,22 @@ int ast_threadpool_push(struct ast_threadpool *pool, int (*task)(void *data), vo
  */
 void ast_threadpool_shutdown(struct ast_threadpool *pool);
 
+/*!
+ * \brief Get the threadpool serializer currently associated with this thread.
+ * \since 14.0.0
+ *
+ * \note The returned pointer is valid while the serializer
+ * thread is running.
+ *
+ * \note Use ao2_ref() on serializer if you are going to keep it
+ * for another thread.  To unref it you must then use
+ * ast_taskprocessor_unreference().
+ *
+ * \retval serializer on success.
+ * \retval NULL on error or no serializer associated with the thread.
+ */
+struct ast_taskprocessor *ast_threadpool_serializer_get_current(void);
+
 /*!
  * \brief Serialized execution of tasks within a \ref ast_threadpool.
  *

main/threadpool.c

@@ -1150,13 +1150,17 @@ static struct serializer *serializer_create(struct ast_threadpool *pool)
 	return ser;
 }
 
+AST_THREADSTORAGE_RAW(current_serializer);
+
 static int execute_tasks(void *data)
 {
 	struct ast_taskprocessor *tps = data;
 
+	ast_threadstorage_set_ptr(&current_serializer, tps);
 	while (ast_taskprocessor_execute(tps)) {
 		/* No-op */
 	}
+	ast_threadstorage_set_ptr(&current_serializer, NULL);
 
 	ast_taskprocessor_unreference(tps);
 	return 0;
@@ -1192,6 +1196,11 @@ static struct ast_taskprocessor_listener_callbacks serializer_tps_listener_callb
 	.shutdown = serializer_shutdown,
 };
 
+struct ast_taskprocessor *ast_threadpool_serializer_get_current(void)
+{
+	return ast_threadstorage_get_ptr(&current_serializer);
+}
+
 struct ast_taskprocessor *ast_threadpool_serializer(const char *name, struct ast_threadpool *pool)
 {
 	RAII_VAR(struct serializer *, ser, NULL, ao2_cleanup);

res/res_pjsip.c

@@ -1864,6 +1864,15 @@
 
 #define MOD_DATA_CONTACT "contact"
 
+/*! Number of serializers in pool if one not supplied. */
+#define SERIALIZER_POOL_SIZE		8
+
+/*! Next serializer pool index to use. */
+static int serializer_pool_pos;
+
+/*! Pool of serializers to use if not supplied. */
+static struct ast_taskprocessor *serializer_pool[SERIALIZER_POOL_SIZE];
+
 static pjsip_endpoint *ast_pjsip_endpoint;
 
 static struct ast_threadpool *sip_threadpool;
@@ -3323,8 +3332,62 @@ struct ast_taskprocessor *ast_sip_create_serializer(void)
 	return serializer;
 }
 
+/*!
+ * \internal
+ * \brief Shutdown the serializers in the default pool.
+ * \since 14.0.0
+ *
+ * \return Nothing
+ */
+static void serializer_pool_shutdown(void)
+{
+	int idx;
+
+	for (idx = 0; idx < SERIALIZER_POOL_SIZE; ++idx) {
+		ast_taskprocessor_unreference(serializer_pool[idx]);
+		serializer_pool[idx] = NULL;
+	}
+}
+
+/*!
+ * \internal
+ * \brief Setup the serializers in the default pool.
+ * \since 14.0.0
+ *
+ * \retval 0 on success.
+ * \retval -1 on error.
+ */
+static int serializer_pool_setup(void)
+{
+	int idx;
+
+	for (idx = 0; idx < SERIALIZER_POOL_SIZE; ++idx) {
+		serializer_pool[idx] = ast_sip_create_serializer();
+		if (!serializer_pool[idx]) {
+			serializer_pool_shutdown();
+			return -1;
+		}
+	}
+	return 0;
+}
+
 int ast_sip_push_task(struct ast_taskprocessor *serializer, int (*sip_task)(void *), void *task_data)
 {
+	if (!serializer) {
+		unsigned int pos;
+
+		/*
+		 * Pick a serializer to use from the pool.
+		 *
+		 * Note: We don't care about any reentrancy behavior
+		 * when incrementing serializer_pool_pos.  If it gets
+		 * incorrectly incremented it doesn't matter.
+		 */
+		pos = serializer_pool_pos++;
+		pos %= SERIALIZER_POOL_SIZE;
+		serializer = serializer_pool[pos];
+	}
+
 	if (serializer) {
 		return ast_taskprocessor_push(serializer, sip_task, task_data);
 	} else {
@@ -3377,18 +3440,10 @@ int ast_sip_push_task_synchronous(struct ast_taskprocessor *serializer, int (*si
 	std.task = sip_task;
 	std.task_data = task_data;
 
-	if (serializer) {
+	if (ast_sip_push_task(serializer, sync_task, &std)) {
-		if (ast_taskprocessor_push(serializer, sync_task, &std)) {
+		ast_mutex_destroy(&std.lock);
-			ast_mutex_destroy(&std.lock);
+		ast_cond_destroy(&std.cond);
-			ast_cond_destroy(&std.cond);
+		return -1;
-			return -1;
-		}
-	} else {
-		if (ast_threadpool_push(sip_threadpool, sync_task, &std)) {
-			ast_mutex_destroy(&std.lock);
-			ast_cond_destroy(&std.cond);
-			return -1;
-		}
 	}
 
 	ast_mutex_lock(&std.lock);
@@ -3679,6 +3734,18 @@ static int load_module(void)
 		return AST_MODULE_LOAD_DECLINE;
 	}
 
+	if (serializer_pool_setup()) {
+		ast_log(LOG_ERROR, "Failed to create SIP serializer pool. Aborting load\n");
+		ast_threadpool_shutdown(sip_threadpool);
+		ast_sip_destroy_system();
+		pj_pool_release(memory_pool);
+		memory_pool = NULL;
+		pjsip_endpt_destroy(ast_pjsip_endpoint);
+		ast_pjsip_endpoint = NULL;
+		pj_caching_pool_destroy(&caching_pool);
+		return AST_MODULE_LOAD_DECLINE;
+	}
+
 	pjsip_tsx_layer_init_module(ast_pjsip_endpoint);
 	pjsip_ua_init_module(ast_pjsip_endpoint, NULL);
 
@@ -3792,6 +3859,7 @@ static int unload_module(void)
 	 */
 	ast_sip_push_task_synchronous(NULL, unload_pjsip, NULL);
 
+	serializer_pool_shutdown();
 	ast_threadpool_shutdown(sip_threadpool);
 
 	ast_sip_destroy_cli();

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 && (
+	if (serializer) {
-		!pjsip_method_cmp(&rdata->msg_info.msg->line.req.method, &pjsip_cancel_method) || 
+		/* We have a serializer so we know where to send the message. */
-		!pjsip_method_cmp(&rdata->msg_info.msg->line.req.method, &pjsip_bye_method)) &&
+	} else if (rdata->msg_info.msg->type == PJSIP_RESPONSE_MSG) {
-		!serializer) {
+		req_serializer = find_request_serializer(rdata);
-		pjsip_endpt_respond_stateless(ast_sip_get_pjsip_endpoint(), rdata, 481, NULL, NULL, NULL);
+		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;
 }

res/res_pjsip/pjsip_resolver.c

@@ -30,6 +30,8 @@
 #include "asterisk/dns_naptr.h"
 #include "asterisk/res_pjsip.h"
 #include "include/res_pjsip_private.h"
+#include "asterisk/taskprocessor.h"
+#include "asterisk/threadpool.h"
 
 #ifdef HAVE_PJSIP_EXTERNAL_RESOLVER
 
@@ -52,6 +54,8 @@ struct sip_resolve {
 	struct ast_dns_query_set *queries;
 	/*! \brief Current viable server addresses */
 	pjsip_server_addresses addresses;
+	/*! \brief Serializer to run async callback into pjlib. */
+	struct ast_taskprocessor *serializer;
 	/*! \brief Callback to invoke upon completion */
 	pjsip_resolver_callback *callback;
 	/*! \brief User provided data */
@@ -97,6 +101,7 @@ static void sip_resolve_destroy(void *data)
 
 	AST_VECTOR_FREE(&resolve->resolving);
 	ao2_cleanup(resolve->queries);
+	ast_taskprocessor_unreference(resolve->serializer);
 }
 
 /*!
@@ -398,7 +403,7 @@ static void sip_resolve_callback(const struct ast_dns_query_set *query_set)
 
 	/* Push a task to invoke the callback, we do this so it is guaranteed to run in a PJSIP thread */
 	ao2_ref(resolve, +1);
-	if (ast_sip_push_task(NULL, sip_resolve_invoke_user_callback, resolve)) {
+	if (ast_sip_push_task(resolve->serializer, sip_resolve_invoke_user_callback, resolve)) {
 		ao2_ref(resolve, -1);
 	}
 
@@ -572,6 +577,8 @@ static void sip_resolve(pjsip_resolver_t *resolver, pj_pool_t *pool, const pjsip
 		return;
 	}
 
+	resolve->serializer = ao2_bump(ast_threadpool_serializer_get_current());
+
 	ast_debug(2, "[%p] Starting initial resolution using parallel queries for target '%s'\n", resolve, host);
 	ast_dns_query_set_resolve_async(resolve->queries, sip_resolve_callback, resolve);