fsm_tmr_cb: don't set T=0, the fi may no longer exist

When calling the timer_cb, that may have effected an fi termination and
deallocation, e.g. from dispatching events and/or complex choices made.

Current timer_cb implementations expect T to reflect the fired timer number, so
we can't actually set T=0 before calling the timer_cb.

Instead, never reset T to zero, let it always reflect the timer that last
fired. When a new timer starts, T will be set to its new value.

Adding a T arg to the timer_cb() would have been the cleanest solution, so that
fi->T can be set to zero before dispatching the timer_cb. But since we've
already rolled out this FSM API, we should stay backwards compatible.

In the case where the timer returned 1 to request termination, we can assume
that the fi still exists, but to be consistent, don't set T = 0 in that code
path either.

Change-Id: I18626b55a1491098b3ed602df1b331f08d25625a

1 files changed, 5 insertions, 4 deletions

diff --git a/src/fsm.c b/src/fsm.c
index 827e8b37..0bdcd9d4 100644
--- a/src/fsm.c
+++ b/src/fsm.c
@@ -183,16 +183,17 @@ static void fsm_tmr_cb(void *data)
 
 	if (fsm->timer_cb) {
 		int rc = fsm->timer_cb(fi);
-		if (rc != 1) {
-			fi->T = 0;
+		if (rc != 1)
+			/* We don't actually know whether fi exists anymore.
+			 * Make sure to not access it and return right away. */
 			return;
-		}
+		/* The timer_cb told us to terminate, so we can safely assume
+		 * that fi still exists. */
 		LOGPFSM(fi, "timer_cb requested termination\n");
 	} else
 		LOGPFSM(fi, "No timer_cb, automatic termination\n");
 
 	/* if timer_cb returns 1 or there is no timer_cb */
-	fi->T = 0;
 	osmo_fsm_inst_term(fi, OSMO_FSM_TERM_TIMEOUT, &T);
 }