bridge: Fix softmix bridge deadlock.

* Fix deadlock in
bridge_softmix.c:softmix_bridge_stream_topology_changed() between
bridge_channel and channel locks.

* The new bridge technology topology change callbacks must be called with
the bridge locked.  The callback references the bridge channel list, the
bridge technology could change, and the bridge stream mapping is updated.

ASTERISK-27212

Change-Id: Ide4360ab853607e738ad471721af3f561ddd83be

2 files changed, 33 insertions, 18 deletions

diff --git a/include/asterisk/bridge_channel.h b/include/asterisk/bridge_channel.h
index 4d3326083..4504d6bcb 100644
--- a/include/asterisk/bridge_channel.h
+++ b/include/asterisk/bridge_channel.h
@@ -716,19 +716,24 @@ void ast_bridge_channel_feature_digit(struct ast_bridge_channel *bridge_channel,
  * \brief Maps a channel's stream topology to and from the bridge
  * \since 15.0.0
  *
- * When a channel joins a bridge or its associated stream topology is updated, each stream
- * in the topology needs to be mapped according to its media type to the bridge. Calling
- * this method creates a mapping of each stream on the channel indexed to the bridge's
- * supported media types and vice versa (i.e. bridge's media types indexed to channel
- * streams).
- *
- * The first channel to join the bridge creates the initial order for the bridge's media
- * types (e.g. a one to one mapping is made). Subsequently added channels are mapped to
- * that order adding more media types if/when the newly added channel has more streams
- * and/or media types specified by the bridge.
+ * \details
+ * When a channel joins a bridge or its associated stream topology is
+ * updated, each stream in the topology needs to be mapped according
+ * to its media type to the bridge.  Calling this method creates a
+ * mapping of each stream on the channel indexed to the bridge's
+ * supported media types and vice versa (i.e. bridge's media types
+ * indexed to channel streams).
+ *
+ * The first channel to join the bridge creates the initial order for
+ * the bridge's media types (e.g. a one to one mapping is made).
+ * Subsequently added channels are mapped to that order adding more
+ * media types if/when the newly added channel has more streams and/or
+ * media types specified by the bridge.
  *
  * \param bridge_channel Channel to map
  *
+ * \note The bridge_channel's bridge must be locked prior to calling this function.
+ *
  * \return Nothing
  */
 void ast_bridge_channel_stream_map(struct ast_bridge_channel *bridge_channel);
diff --git a/include/asterisk/bridge_technology.h b/include/asterisk/bridge_technology.h
index 8cebe9326..def7b1933 100644
--- a/include/asterisk/bridge_technology.h
+++ b/include/asterisk/bridge_technology.h
@@ -164,20 +164,30 @@ struct ast_bridge_technology {
 	/*!
 	 * \brief Callback for when a request has been made to change a stream topology on a channel
 	 *
-	 * This is called when a bridge receives a request to change the topology on the channel. A bridge
-	 * technology should define a handler for this callback if it needs to update internals or intercept
-	 * the request and not pass it on to other channels. This can be done by returning a nonzero value.
+	 * \details
+	 * This is called when a bridge receives a request to change the
+	 * topology on the channel.  A bridge technology should define a
+	 * handler for this callback if it needs to update internals or
+	 * intercept the request and not pass it on to other channels.
+	 * This can be done by returning a nonzero value.
 	 *
-	 * \retval 0 Frame accepted by the bridge.
-	 * \retval -1 Frame rejected.
+	 * \retval 0 Frame can pass to the bridge technology.
+	 * \retval non-zero Frame intercepted by the bridge technology.
+	 *
+	 * \note On entry, bridge is already locked.
 	 */
 	int (*stream_topology_request_change)(struct ast_bridge *bridge, struct ast_bridge_channel *bridge_channel);
 	/*!
 	 * \brief Callback for when a stream topology changes on the channel
 	 *
-	 * This is called when a bridge receives an indication that a topology has been changed on a channel
-	 * and the new topology has been mapped to the bridge. A bridge technology should define a handler for
-	 * this callback if it needs to update internals due to a channel's topology changing.
+	 * \details
+	 * This is called when a bridge receives an indication that a
+	 * topology has been changed on a channel and the new topology has
+	 * been mapped to the bridge.  A bridge technology should define a
+	 * handler for this callback if it needs to update internals due
+	 * to a channel's topology changing.
+	 *
+	 * \note On entry, bridge is already locked.
 	 */
 	void (*stream_topology_changed)(struct ast_bridge *bridge, struct ast_bridge_channel *bridge_channel);
 	/*! TRUE if the bridge technology is currently suspended. */