Ensure channel locks aren't held while calling ast_set_variables.

If the channel is locked when calling ast_set_variables and any of the
variables contained dialplan functions, there's a possiblilty of a deadlock.
To prevent this, either the explicit locks were removed or the call to
ast_set_variables moved out of the lock scope.  A warning to not hold
channel locks is also added to the documentation for ast_set_variables.

Resolves: #1936

include/asterisk/channel.h

@@ -2749,7 +2749,8 @@ void ast_channel_inherit_variables(const struct ast_channel *parent, struct ast_
  * \param chan the channel
  * \param vars a linked list of variables
  *
- * \pre chan is locked
+ * \warning The channel must not be locked if there's a possibility that
+ * a dialplan function would be invoked.
  *
  * \details
  * Variable names can be for a regular channel variable or a dialplan function

main/channel.c

@@ -5950,9 +5950,7 @@ struct ast_channel *ast_call_forward(struct ast_channel *caller, struct ast_chan
 	/* Copy/inherit important information into new channel */
 	if (oh) {
 		if (oh->vars) {
-			ast_channel_lock(new_chan);
 			ast_set_variables(new_chan, oh->vars);
-			ast_channel_unlock(new_chan);
 		}
 		if (oh->parent_channel) {
 			call_forward_inherit(new_chan, oh->parent_channel, orig);
@@ -6017,9 +6015,7 @@ struct ast_channel *__ast_request_and_dial(const char *type, struct ast_format_c
 
 	if (oh) {
 		if (oh->vars) {
-			ast_channel_lock(chan);
 			ast_set_variables(chan, oh->vars);
-			ast_channel_unlock(chan);
 		}
 		if (!ast_strlen_zero(oh->cid_num) && !ast_strlen_zero(oh->cid_name)) {
 			/*

main/pbx.c

@@ -7817,10 +7817,10 @@ static int pbx_outgoing_attempt(const char *type, struct ast_format_cap *cap,
 		return -1;
 	}
 
-	ast_channel_lock(dialed);
 	if (vars) {
 		ast_set_variables(dialed, vars);
 	}
+	ast_channel_lock(dialed);
 	if (!ast_strlen_zero(account)) {
 		ast_channel_stage_snapshot(dialed);
 		ast_channel_accountcode_set(dialed, account);
@@ -8005,10 +8005,10 @@ int ast_pbx_outgoing_exten_predial(const char *type, struct ast_format_cap *cap,
 		if (failed) {
 			char failed_reason[12];
 
-			ast_set_variables(failed, vars);
 			snprintf(failed_reason, sizeof(failed_reason), "%d", *reason);
 			pbx_builtin_setvar_helper(failed, "REASON", failed_reason);
 			ast_channel_unlock(failed);
+			ast_set_variables(failed, vars);
 
 			if (ast_pbx_run(failed)) {
 				ast_log(LOG_ERROR, "Unable to run PBX on '%s'\n",

res/ari/resource_channels.c

@@ -1372,7 +1372,6 @@ static struct ast_channel *ari_channels_handle_originate_with_id(const char *arg
 		ast_channel_set_connected_line(chan, &connected, NULL);
 	}
 
-	ast_channel_lock(chan);
 	if (variables) {
 		ast_set_variables(chan, variables);
 	}
@@ -1392,7 +1391,6 @@ static struct ast_channel *ari_channels_handle_originate_with_id(const char *arg
 	}
 
 	snapshot = ast_channel_snapshot_get_latest(ast_channel_uniqueid(chan));
-	ast_channel_unlock(chan);
 
 	/* Before starting the async dial bump the ref in case the dial quickly goes away and takes
 	 * the reference with it