net: TestDialerDualStack fails with "i/o timeout" or "got 5.81849453s; want <= 95ms"

[mdempsky]

TestDialerDualStack is commonly flaking on OpenBSD and Windows, albeit with different error messages:

https://www.google.com/search?q=TestDialerDualStack+openbsd+site%3Abuild.golang.org

--- FAIL: TestDialerDualStack (14.78s)
    dial_test.go:633: got 5.81849453s; want <= 95ms

https://www.google.com/search?q=TestDialerDualStack+windows+site%3Abuild.golang.org

--- FAIL: TestDialerDualStack (5.30s)
    dial_test.go:664: dial tcp 127.0.0.1:2651: i/o timeout

[mikioh]

This looks different from #15316, #15574. It happened on active open side, and it took 5s for a simple dial call, strange.

[mikioh]

Funny, I got "PASS: TestDialerDualStack (5.99s)" when I ran TestDialerDualStack on openbsd59-vm like the following:

go test -run=TestDialerDualStack$ -v -count=100 net
=== RUN   TestDialerDualStack
--- PASS: TestDialerDualStack (0.00s)
(snip)
=== RUN   TestDialerDualStack
--- PASS: TestDialerDualStack (5.99s)
=== RUN   TestDialerDualStack
--- PASS: TestDialerDualStack (0.00s)
=== RUN   TestDialerDualStack
PASS
Socket statistical information:
(inet4, stream, default): opened=900 connected=200 listened=300 accepted=0 closed=900 openfailed=0 connectfailed=400 listenfailed=0 acceptfailed=0 closefailed=0
(inet6, stream, default): opened=400 connected=200 listened=200 accepted=50 closed=450 openfailed=0 connectfailed=0 listenfailed=0 acceptfailed=100 closefailed=0

and this is not related to runtime/GC stuff because I got the same result when GOGC=off.

[mikioh]

Hm,

openbsd-amd64:~/$ go test -run=DualStack$ -count=50 net
ok      net     6.042s
openbsd-amd64:~/$ go test -run=DualStack$ -count=100 net
ok      net     18.048s

dragonfly-amd64:~/$ go test -run=DualStack$ -count=50 net
ok      net 0.075s
dragonfly-amd64:~/$ go test -run=DualStack$ -count=100 net
ok      net 1.136s

[bradfitz]

Another on windows-386:
https://storage.googleapis.com/go-build-log/d93c922c/windows-386-gce_fb3d6a91.log

[adg]

cc @aclements, would you please run your failure analysis tool against this?