time, runtime: zero duration timer takes 2 minutes to fire #44868
Description
Very rarely, zero duration timers fail to fire for 2 minutes. This program will occassionally fail. e.g.,
$ while ./timer; do echo again; done
again
again
again
again
again
again
again
again
again
panic: Expected time to get value from Timer channel to be less than 2 sec, took 2m0.006359722s, time on channel is 2021-03-08 15:17:38.623999432 -0500 EST m=+120.798106019, current time is 2021-03-08 15:17:38.624042501 -0500 EST m=+120.798149081
This reproduces on 1.16 (linux-amd64, other platforms not tested), but not 1.15. Thus this is probably more fallout from http://golang.org/cl/232298.
Failure seems to consistently occur at 2 minutes, which is a strong indication that this is related to the 2 minute force GC period. Most likely the scheduler is completely missing the timer until forced GC kicks it awake again. That makes this distinct from #44343, where timer expiration is slower but never missed.