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

1 files changed, 51 insertions, 21 deletions

diff --git a/res/stasis/stasis_bridge.c b/res/stasis/stasis_bridge.c
index 657238417..e41088134 100644
--- a/res/stasis/stasis_bridge.c
+++ b/res/stasis/stasis_bridge.c
@@ -99,6 +99,56 @@ static void bridge_stasis_queue_join_action(struct ast_bridge *self,
 
 /*!
  * \internal
+ * \brief Peek at channel before it is pushed into bridge
+ * \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.
+ *
+ * \retval 0 on success.
+ * \retval -1 on failure.  The channel should not be pushed.
+ */
+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 *swap_control;
+	struct ast_channel_snapshot *to_be_replaced;
+
+	if (!swap) {
+		goto done;
+	}
+
+	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));
+
+	ast_channel_lock(bridge_channel->chan);
+
+	/* copy the app name from the swap channel */
+	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);
+
+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
  *
@@ -115,27 +165,6 @@ static int bridge_stasis_push(struct ast_bridge *self, struct ast_bridge_channel
 {
 	struct stasis_app_control *control = stasis_app_control_find_by_channel(bridge_channel->chan);
 
-	if (swap) {
-		struct ast_channel_snapshot *to_be_replaced = ast_channel_snapshot_get_latest(ast_channel_uniqueid(swap->chan));
-		struct stasis_app_control *swap_control = stasis_app_control_find_by_channel(swap->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)));
-		}
-		ast_channel_unlock(bridge_channel->chan);
-		ao2_cleanup(to_be_replaced);
-		ao2_cleanup(swap_control);
-	}
-
 	if (!control && !stasis_app_channel_is_internal(bridge_channel->chan)) {
 		/* channel not in Stasis(), get it there */
 		/* Attach after-bridge callback and pass ownership of swap_app to it */
@@ -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;
 }