ctrl: fix deferred commands (and hence fix osmo-bts-sysmo 'clock-info' cmd)

The CTRL interface has a ctrl_cmd_def_* API that allows deferring a CTRL
command reply until later. However, the command handling currently fails to
acknowledge this and deallocates the struct ctrl_cmd anyway.

Fix: in struct ctrl_cmd, add a defer pointer to be populated by
ctrl_cmd_def_make(). A cmd thus marked as deferred is not deallocated at the
end of command handling. This fix needs no change in calling code.

(Another idea was to return a different code than CTRL_CMD_HANDLED when the
command is to be deferred, but that would require adjusting each user of
ctrl_cmd_def_make(). The implicit marking is safer and easier.)

Show that handling deferred commands is fixed by adjusting the expectations of
ctrl_test.c's test_deferred_cmd() and removing the now obsolete exit_early
label.

One symptom of the breakage is that osmo-bts-sysmo crashes when asked to report
a trx's clock-info, which is aggravated by the fact that the sysmobts-mgr does
ask osmo-bts-sysmo for a clock-info.

The crash appears since Id583b413f8b8bd16e5cf92a8a9e8663903646381 -- it looked
like just fixing an obvious memory leak, which it did as shown by the unit
test, but deferred ctrl commands actually relied on that leak. Both fixed now.

Related: OS#3120
Change-Id: I24232be7dcf7be79f4def91ddc8b8f8005b56318

2 files changed, 8 insertions, 0 deletions

diff --git a/src/ctrl/control_cmd.c b/src/ctrl/control_cmd.c
index c747e84d..fb0cd2b7 100644
--- a/src/ctrl/control_cmd.c
+++ b/src/ctrl/control_cmd.c
@@ -566,6 +566,7 @@ ctrl_cmd_def_make(const void *ctx, struct ctrl_cmd *cmd, void *data, unsigned in
 
 	cd = talloc_zero(ctx, struct ctrl_cmd_def);
 
+	cmd->defer = cd;
 	cd->cmd = cmd;
 	cd->data = data;
 
diff --git a/src/ctrl/control_if.c b/src/ctrl/control_if.c
index 07de0d46..df8abbc6 100644
--- a/src/ctrl/control_if.c
+++ b/src/ctrl/control_if.c
@@ -401,6 +401,13 @@ int ctrl_handle_msg(struct ctrl_handle *ctrl, struct ctrl_connection *ccon, stru
 	if (cmd->type != CTRL_TYPE_ERROR) {
 		cmd->ccon = ccon;
 		if (ctrl_cmd_handle(ctrl, cmd, ctrl->data) == CTRL_CMD_HANDLED) {
+
+			if (cmd->defer) {
+				/* The command is still stored as ctrl_cmd_def.cmd, in the def_cmds list.
+				 * Just leave hanging for deferred handling. Reply will happen later. */
+				return 0;
+			}
+
 			/* On CTRL_CMD_HANDLED, no reply needs to be sent back. */
 			talloc_free(cmd);
 			cmd = NULL;