laforge has submitted this change. (
https://gerrit.osmocom.org/c/osmo-bts/+/42851?usp=email )
Change subject: osmo-bts-trx: shut down on stale clock indication from
transceiver
......................................................................
osmo-bts-trx: shut down on stale clock indication from transceiver
We expect the transceiver to be a reliable, monotonic clock source.
If it reports an FN far behind our local timer (elapsed_fn < 0) while
far more wall-clock time elapsed than its FN advance accounts for,
its clock has likely stalled and the indication carries a stale frame
number. Acting on it drags the scheduler backwards and re-transmits
already-sent TDMA frames, corrupting lchan-internal state(s).
Detect this and shut down the process, same rationale as the existing
"PC clock skew too high" check in trx_fn_timer_cb().
Change-Id: If787ab7ed70aa2dcb0389ceb58620c2302c3431a
AI-Assisted: yes (Claude)
Related: OS#7020, OS#6794
---
M src/osmo-bts-trx/scheduler_trx.c
1 file changed, 16 insertions(+), 0 deletions(-)
Approvals:
laforge: Looks good to me, approved
Jenkins Builder: Verified
pespin: Looks good to me, but someone else must approve
diff --git a/src/osmo-bts-trx/scheduler_trx.c b/src/osmo-bts-trx/scheduler_trx.c
index 770a54b..105ad38 100644
--- a/src/osmo-bts-trx/scheduler_trx.c
+++ b/src/osmo-bts-trx/scheduler_trx.c
@@ -576,6 +576,22 @@
/* check for max clock skew */
if (elapsed_fn > MAX_FN_SKEW || elapsed_fn < -MAX_FN_SKEW) {
+ /* If the transceiver reports an FN far BEHIND our local timer
+ * (elapsed_fn < 0) while far more wall-clock time elapsed than
its FN
+ * advance accounts for (error_us_since_clk large positive),
then its
+ * clock has stalled and this CLCK.ind carries a stale
(outdated) frame
+ * number. Acting on a stale indication would drag the
scheduler backwards
+ * and corrupt lchan-internal state(s). Treat this as a fatal
condition
+ * and shut down -- same rationale as the "PC clock skew too
high"
+ * check in trx_fn_timer_cb(). */
+ if (elapsed_fn < 0 &&
+ error_us_since_clk > (int64_t)GSM_TDMA_FN_DURATION_uS *
MAX_FN_SKEW) {
+ LOGP(DL1C, LOGL_FATAL, "Stale CLCK.ind: fn=%u is
%"PRId64" us behind\n",
+ fn, error_us_since_clk);
+ osmo_timerfd_disable(&tcs->fn_timer_ofd);
+ bts_shutdown(bts, "TRX clock skew too high");
+ return -1;
+ }
LOGP(DL1C, LOGL_NOTICE, "GSM clock skew: old fn=%u, "
"new fn=%u\n", tcs->last_fn_timer.fn, fn);
return trx_setup_clock(bts, tcs, &tv_now, &interval, fn);
--
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Gerrit-MessageType: merged
Gerrit-Project: osmo-bts
Gerrit-Branch: master
Gerrit-Change-Id: If787ab7ed70aa2dcb0389ceb58620c2302c3431a
Gerrit-Change-Number: 42851
Gerrit-PatchSet: 2
Gerrit-Owner: fixeria <[email protected]>
Gerrit-Reviewer: Jenkins Builder
Gerrit-Reviewer: laforge <[email protected]>
Gerrit-Reviewer: pespin <[email protected]>
