Added deadlock protection to try_suggested_sip_codec in chan_sip.c.

Review: https://reviewboard.asterisk.org/r/287/


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@202022 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -3729,8 +3729,20 @@ static void try_suggested_sip_codec(struct sip_pvt *p)
 	int fmt;
 	const char *codec;
 
-	codec = pbx_builtin_getvar_helper(p->owner, "SIP_CODEC");
-	if (!codec) 
+	while (p->owner && ast_channel_trylock(p->owner)) {
+		sip_pvt_unlock(p);
+		sched_yield();
+		sip_pvt_lock(p);
+	}
+
+	if (!p->owner)
+		return;
+
+	codec = ast_strdupa(S_OR(pbx_builtin_getvar_helper(p->owner, "SIP_CODEC"), ""));
+
+	ast_channel_unlock(p->owner);
+
+	if (ast_strlen_zero(codec))
 		return;
 
 	fmt = ast_getformatbyname(codec);