I'm testing on rs_preview build 14915.

Running the .NET CoreFx System.Net.Http functional tests, I pretty reliably have test failures due to epoll_ctl(…, EPOLL_CTL_ADD, …) returning EEXIST. This does not occur on "real" Ubuntu.

I only see this if I allow the tests to run in parallel; when run sequentially, they all pass. So I assume this is some sort of concurrency-related bug. I’ve tried putting together a smaller repro, but haven’t had any luck. Here are the repro steps:

1. Install the .NET Core SDK
2. Get a build of System.Net.Http.Functional.Tests from my branch of CoreFx (I'll send binaries I've built, privately).
3. Run the tests:

./corerun xunit.console.netcore.exe System.Net.Http.Functional.Tests.dll -notrait Benchmark=true -notrait category=nonnetcoreapp1.0tests -notrait category=failing -notrait category=nonlinuxtests

Most of the time when I run these, at least one test fails with output like this:

      System.Net.InternalException : Exception of type 'System.Net.InternalException' was thrown.
      Stack Trace:
            at System.Net.Sockets.SocketAsyncContext.Register(SocketEvents events)
            ...

Sometimes I've also seen the test hang. This may or may not be related; I haven't investigated the hang yet.

Very occasionally, the test passes. Run it again a couple of times, and you should see the failure in SocketAsyncContext.Register (which calls epoll_ctl).