app_rpt: Acquire blocklock mutex when hard hanging up link channel.

Resolves: #459

apps/app_rpt.c

@@ -4154,7 +4154,7 @@ static inline void free_frame(struct ast_frame **f)
 }
 
 /*! \brief Safely hang up any channel, even if a PBX could be running on it */
-static inline void safe_hangup(struct ast_channel *chan)
+static inline void safe_hangup(struct rpt *myrpt, struct ast_channel *chan)
 {
 	/* myrpt is locked here, so we can trust this will be an atomic operation,
 	 * since we also lock before setting the pbx to NULL */
@@ -4163,15 +4163,19 @@ static inline void safe_hangup(struct ast_channel *chan)
 		ast_softhangup(chan, AST_SOFTHANGUP_EXPLICIT);
 	} else {
 		ast_debug(3, "Hard hanging up channel %s\n", ast_channel_name(chan));
+		/* Another thread could be servicing the channel right now...
+		 * so acquire the block lock to ensure we have exclusive control first. */
+		rpt_mutex_lock(&myrpt->blocklock);
 		ast_hangup(chan);
+		rpt_mutex_unlock(&myrpt->blocklock);
 	}
 }
 
 /*! \note myrpt->lock must be held when calling */
-static inline void hangup_link_chan(struct rpt_link *l)
+static inline void hangup_link_chan(struct rpt *myrpt, struct rpt_link *l)
 {
 	if (l->chan) {
-		safe_hangup(l->chan);
+		safe_hangup(myrpt, l->chan);
 		l->chan = NULL;
 	}
 }