From 06ac9b40ed600cd36e1c0a158eb8f2ca01b1941f Mon Sep 17 00:00:00 2001 From: Neels Hofmeyr Date: Tue, 20 Dec 2016 12:05:19 +0100 Subject: fsm: term: safer iteration to remove all child FSMs When terminating child FSMs, restart iteration after every child, to make sure that we don't terminate a child twice. Terminating one child may emit events that in turn terminates other children. I created this patch because at first it looked like the cause of a bug, which turned out not to be the case. So I have no actual use case of this situation, but it does generally make sense to me, so submitting this. Change-Id: I00990b47e42eeb43707a9a42abcd9df52fe5f483 --- src/fsm.c | 24 ++++++++++++++++++++---- 1 file changed, 20 insertions(+), 4 deletions(-) (limited to 'src/fsm.c') diff --git a/src/fsm.c b/src/fsm.c index 67175388..16699fab 100644 --- a/src/fsm.c +++ b/src/fsm.c @@ -427,17 +427,33 @@ void _osmo_fsm_inst_term(struct osmo_fsm_inst *fi, enum osmo_fsm_term_cause cause, void *data, const char *file, int line) { - struct osmo_fsm_inst *child, *child2; + struct osmo_fsm_inst *first_child, *last_seen_first_child; struct osmo_fsm_inst *parent = fi->proc.parent; uint32_t parent_term_event = fi->proc.parent_term_event; LOGPFSMSRC(fi, file, line, "Terminating (cause = %s)\n", osmo_fsm_term_cause_name(cause)); - /* iterate over all children */ - llist_for_each_entry_safe(child, child2, &fi->proc.children, proc.child) { + /* iterate over all children, starting from the beginning every time: + * terminating an FSM may emit events that cause other FSMs to also + * terminate and remove themselves from this list. */ + last_seen_first_child = NULL; + while (!llist_empty(&fi->proc.children)) { + first_child = llist_entry(fi->proc.children.next, + typeof(*first_child), + proc.child); + + /* paranoia: do not loop forever */ + if (first_child == last_seen_first_child) { + LOGPFSMLSRC(fi, LOGL_ERROR, file, line, + "Internal error while terminating child" + " FSMs: a child FSM is stuck\n"); + break; + } + last_seen_first_child = first_child; + /* terminate child */ - _osmo_fsm_inst_term(child, OSMO_FSM_TERM_PARENT, NULL, + _osmo_fsm_inst_term(first_child, OSMO_FSM_TERM_PARENT, NULL, file, line); } -- cgit v1.2.3