stasis transfer: fix stasis bridge push race part two

When swapping a Local channel in place of one already
in a bridge (to complete a bridge attended transfer),
the channel that was swapped out can actually be hung
up before the stasis bridge push callback executes on
the independant transfer thread.  This results in the
stasis app loop dropping out and removing the control
that has the the app name which the local replacement
channel needs so it can re-enter stasis.

To avoid this race condition a new push_peek callback
has been added, and called from the ast_bridge_impart
thread before it launches the independant thread that
will complete the transfer.  Now the stasis push_peek
callback can copy the stasis app name before the swap
channel can hang up.

ASTERISK-24649
Review: https://reviewboard.asterisk.org/r/4382/
........

Merged revisions 431450 from http://svn.asterisk.org/svn/asterisk/branches/13


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@431451 65c4cc65-6c06-0410-ace0-fbb531ad65f3

include/asterisk/bridge.h

@@ -241,6 +241,8 @@ struct ast_bridge_methods {
 	ast_bridge_notify_masquerade_fn notify_masquerade;
 	/*! Get the bridge merge priority. */
 	ast_bridge_merge_priority_fn get_merge_priority;
+	/*! Peek at swap channel before it can hang up, prior to push. */
+	ast_bridge_push_channel_fn push_peek;
 };
 
 /*! Softmix technology parameters. */

main/bridge.c

@@ -904,6 +904,26 @@ static int bridge_base_get_merge_priority(struct ast_bridge *self)
 	return 0;
 }
 
+/*!
+ * \internal
+ * \brief ast_bridge base push_peek method.
+ * \since 13.2.0
+ *
+ * \param self Bridge to operate upon.
+ * \param bridge_channel Bridge channel to push.
+ * \param swap Bridge channel to swap places with if not NULL.
+ *
+ * \note On entry, self is already locked.
+ * \note Stub because of nothing to do.
+ *
+ * \retval 0 on success
+ * \retval -1 on failure
+ */
+static int bridge_base_push_peek(struct ast_bridge *self, struct ast_bridge_channel *bridge_channel, struct ast_bridge_channel *swap)
+{
+	return 0;
+}
+
 struct ast_bridge_methods ast_bridge_base_v_table = {
 	.name = "base",
 	.destroy = bridge_base_destroy,
@@ -912,6 +932,7 @@ struct ast_bridge_methods ast_bridge_base_v_table = {
 	.pull = bridge_base_pull,
 	.notify_masquerade = bridge_base_notify_masquerade,
 	.get_merge_priority = bridge_base_get_merge_priority,
+	.push_peek = bridge_base_push_peek,
 };
 
 struct ast_bridge *ast_bridge_base_new(uint32_t capabilities, unsigned int flags, const char *creator, const char *name, const char *id)
@@ -1589,6 +1610,18 @@ int ast_bridge_join(struct ast_bridge *bridge,
 	bridge_channel->features = features;
 	bridge_channel->inhibit_colp = !!(flags & AST_BRIDGE_JOIN_INHIBIT_JOIN_COLP);
 
+	/* allow subclass to peek at upcoming push operation */
+	if (bridge->v_table->push_peek && !res) {
+		struct ast_bridge_channel *bcswap = NULL;
+
+		ast_bridge_lock(bridge);
+		if (bridge_channel->swap) {
+			bcswap = bridge_find_channel(bridge, bridge_channel->swap);
+		}
+		res = bridge->v_table->push_peek(bridge, bridge_channel, bcswap);
+		ast_bridge_unlock(bridge);
+	}
+
 	if (!res) {
 		res = bridge_channel_internal_join(bridge_channel);
 	}
@@ -1724,6 +1757,18 @@ int ast_bridge_impart(struct ast_bridge *bridge,
 		(flags & AST_BRIDGE_IMPART_CHAN_MASK) == AST_BRIDGE_IMPART_CHAN_DEPARTABLE;
 	bridge_channel->callid = ast_read_threadstorage_callid();
 
+	/* allow subclass to peek at swap channel before it can hangup */
+	if (bridge->v_table->push_peek && !res) {
+		struct ast_bridge_channel *bcswap = NULL;
+
+		ast_bridge_lock(bridge);
+		if (bridge_channel->swap) {
+			bcswap = bridge_find_channel(bridge, bridge_channel->swap);
+		}
+		res = bridge->v_table->push_peek(bridge, bridge_channel, bcswap);
+		ast_bridge_unlock(bridge);
+	}
+
 	/* Actually create the thread that will handle the channel */
 	if (!res) {
 		if ((flags & AST_BRIDGE_IMPART_CHAN_MASK) == AST_BRIDGE_IMPART_CHAN_INDEPENDENT) {

res/stasis/stasis_bridge.c

@@ -99,8 +99,8 @@ static void bridge_stasis_queue_join_action(struct ast_bridge *self,
 
 /*!
  * \internal
- * \brief Push this channel into the Stasis bridge.
+ * \brief Peek at channel before it is pushed into bridge
- * \since 12.5.0
+ * \since 13.2.0
  *
  * \param self Bridge to operate upon.
  * \param bridge_channel Bridge channel to push.
@@ -109,32 +109,61 @@ static void bridge_stasis_queue_join_action(struct ast_bridge *self,
  * \note On entry, self is already locked.
  *
  * \retval 0 on success.
- * \retval -1 on failure.  The channel did not get pushed.
+ * \retval -1 on failure.  The channel should not be pushed.
  */
-static int bridge_stasis_push(struct ast_bridge *self, struct ast_bridge_channel *bridge_channel, struct ast_bridge_channel *swap)
+static int bridge_stasis_push_peek(struct ast_bridge *self, struct ast_bridge_channel *bridge_channel, struct ast_bridge_channel *swap)
 {
-	struct stasis_app_control *control = stasis_app_control_find_by_channel(bridge_channel->chan);
+	struct stasis_app_control *swap_control;
+	struct ast_channel_snapshot *to_be_replaced;
 
-	if (swap) {
+	if (!swap) {
-		struct ast_channel_snapshot *to_be_replaced = ast_channel_snapshot_get_latest(ast_channel_uniqueid(swap->chan));
+		goto done;
-		struct stasis_app_control *swap_control = stasis_app_control_find_by_channel(swap->chan);
+	}
+
+	swap_control = stasis_app_control_find_by_channel(swap->chan);
+	if (!swap_control) {
+		ast_log(LOG_ERROR,"Failed to find stasis app control for swapped channel %s\n", ast_channel_name(swap->chan));
+		return -1;
+	}
+	to_be_replaced = ast_channel_snapshot_get_latest(ast_channel_uniqueid(swap->chan));
+
+	ast_debug(3, "Copying stasis app name %s from %s to %s\n", app_name(control_app(swap_control)),
+		ast_channel_name(swap->chan), ast_channel_name(bridge_channel->chan));
 
-		/* set the replace channel snapshot */
 	ast_channel_lock(bridge_channel->chan);
-		app_set_replace_channel_snapshot(bridge_channel->chan, to_be_replaced);
 
 	/* copy the app name from the swap channel */
-		if (swap_control) {
-			ast_debug(3, "Copying stasis app name %s from %s to %s\n",
-				app_name(control_app(swap_control)),
-				ast_channel_name(swap->chan),
-				ast_channel_name(bridge_channel->chan));
 	app_set_replace_channel_app(bridge_channel->chan, app_name(control_app(swap_control)));
-		}
+
+	/* set the replace channel snapshot */
+	app_set_replace_channel_snapshot(bridge_channel->chan, to_be_replaced);
+
 	ast_channel_unlock(bridge_channel->chan);
+
+	ao2_ref(swap_control, -1);
 	ao2_cleanup(to_be_replaced);
-		ao2_cleanup(swap_control);
+
-	}
+done:
+	return ast_bridge_base_v_table.push_peek(self, bridge_channel, swap);
+}
+
+/*!
+ * \internal
+ * \brief Push this channel into the Stasis bridge.
+ * \since 12.5.0
+ *
+ * \param self Bridge to operate upon.
+ * \param bridge_channel Bridge channel to push.
+ * \param swap Bridge channel to swap places with if not NULL.
+ *
+ * \note On entry, self is already locked.
+ *
+ * \retval 0 on success.
+ * \retval -1 on failure.  The channel did not get pushed.
+ */
+static int bridge_stasis_push(struct ast_bridge *self, struct ast_bridge_channel *bridge_channel, struct ast_bridge_channel *swap)
+{
+	struct stasis_app_control *control = stasis_app_control_find_by_channel(bridge_channel->chan);
 
 	if (!control && !stasis_app_channel_is_internal(bridge_channel->chan)) {
 		/* channel not in Stasis(), get it there */
@@ -256,4 +285,5 @@ void bridge_stasis_init(void)
 	bridge_stasis_v_table.name = "stasis";
 	bridge_stasis_v_table.push = bridge_stasis_push;
 	bridge_stasis_v_table.pull = bridge_stasis_pull;
+	bridge_stasis_v_table.push_peek = bridge_stasis_push_peek;
 }