net: TestDialerDualStackFDLeak failures due to "i/o timeout" on solaris-amd64-oraclerel builder

[bcmills]

2020-10-30T14:13:03-733c4af/solaris-amd64-oraclerel
2020-10-29T13:53:33-c45d780/solaris-amd64-oraclerel
2020-10-28T19:28:08-87d59bc/solaris-amd64-oraclerel
2020-10-28T00:48:22-49b017f/solaris-amd64-oraclerel

[bcmills]

This is probably related to #41629.

[bcmills]

CC @rorth @fraenkel @bradfitz @ianlancetaylor

[rorth]

As an initial test, I've built trunk on an identical system and ran net.test in a tight loop of net.test -test.run TestDialerDualStackFDLeak On an unloaded system, I got no failure at all in 30000+ runs. I've than repeated the test on the host of the builder (under some load due to 3 different buildbots total running there): here I find 7 FAILs out of ca. 68000 runs. Adding some load on the initial system, I get some FAILs, too (2 out of 60000). The question is how best to proceed from here.