sched: Downgrade warning log to info in KIST

Some platforms don't have good monotonic time support so don't warn when the
diff between the last run of the scheduler time and now is negative. The
scheduler recovers properly from this so no need to be noisy.

Fixes #23696

Signed-off-by: David Goulet <dgoulet@torproject.org>

changes/bug23696

@@ -0,0 +1,5 @@
+  o Minor bugfix (KIST scheduler):
+    - Downgrade a warning to log info when the monotonic time diff is
+      negative. This can happen on platform not supporting monotonic time. The
+      scheduler recovers from this without any problem. Fixes ticket 23969;
+      bugfix on 0.3.2.1-alpha.

src/or/scheduler_kist.c

@@ -525,9 +525,13 @@ kist_scheduler_schedule(void)
   monotime_get(&now);
 
   /* If time is really monotonic, we can never have now being smaller than the
-   * last scheduler run. The scheduler_last_run at first is set to 0. */
+   * last scheduler run. The scheduler_last_run at first is set to 0.
+   * Unfortunately, not all platforms guarantee monotonic time so we log at
+   * info level but don't make it more noisy. */
   diff = monotime_diff_msec(&scheduler_last_run, &now);
-  IF_BUG_ONCE(diff < 0) {
+  if (diff < 0) {
+    log_info(LD_SCHED, "Monotonic time between now and last run of scheduler "
+                       "is negative: %" PRId64 ". Setting diff to 0.", diff);
     diff = 0;
   }
   if (diff < sched_run_interval) {