Request for help / ideas to debug issue

[John Lenton]

Hello!

We're seeing a weird issue with either go, pthreads, or the kernel. If
you're knowledgeable about one or more of those things, could you take
a look? Thank you.

The issue manifests as nasty warnings from the "snap run" command,
which is also the first step into a snapped app or service. It looks
like

runtime/cgo: pthread_create failed: Resource temporarily unavailable

a very stripped-down reproducer is http://pastebin.ubuntu.com/24150663/

build that, run it in a loop, and you'll see a bunch of those messages
(and some weirder ones, but let's take it one step at a time).

if you comment out the 'import "C"' line the message will change but
still happen, which makes me think that at least in part this is a Go
issue (or that we're holding it wrong).

Note that the exec does work; the warning seems to come from a
different thread than the one doing the Exec (the other clue that
points in this direction is that sometimes the message is truncated).
You can verify the fact that it does run by changing the /bin/true to
/bin/echo os.Args[1], but because this issue is obviously a race
somewhere, this change makes it less likely to happen (from ~10% down
to ~.5% of runs, in my machines).

One thing that makes this harder to debug is that strace'ing the
process hangs (hard, kill -9 of strace to get out) before reproducing
the issue. This probably means we need to trace it at a lower level,
and I don't know enough about tracing a process group from inside the
kernel to be able to do that; what I can find about kernel-level
tracing is around syscalls or devices.

Ideas?