Before we get into this, what is the actual problem here? Just the ugly messages?
On 11 March 2017 at 02:58, Alfonso Sanchez-Beato < alfonso.sanchez-be...@canonical.com> wrote: > On Fri, Mar 10, 2017 at 10:22 AM, John Lenton <john.len...@canonical.com> > wrote: > > > 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) > Turns out this was fixed in Go 1.8: https://go-review.googlesource.com/c/33894/ > > 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). > ... but only in the non-cgo case, you can (occasionally) still get messages like: runtime: failed to create new OS thread (have 5 already; errno=11) runtime: may need to increase max user processes (ulimit -u) fatal error: newosproc if you comment out the import "C". I guess we should report that upstream. > > 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? > > > > I found this related thread: > > https://groups.google.com/forum/#!msg/golang-nuts/8gszDBRZh_4/lhROTfN9TxIJ > > << > I believe this can happen on GNU/Linux if your program uses cgo and if > thread A is in the Go runtime starting up a new thread B while thread > C is execing a program. The underlying cause is that while one thread > is calling exec the Linux kernel will fail attempts by other threads > to call clone by returning EAGAIN. (Look for uses of the in_exec > field in the kernel sources.) > >> > Yeah, this seems to be very accurate. It's also why it seems this is a cosmetic problem only, some thread not calling exec fails, but well, the thread is about to die anyway. > Something like adding a little sleep removes the traces, for instance: > > http://paste.ubuntu.com/24151637/ > > where the program run sleep for 1ms before calling Exec. For smaller units > (say, 20 us) the issue still happens. > > It looks to me that right before running main(), go creates some threads, > calling clone() and probably getting the race described in the thread. As > anyway you are running Exec I guess the traces are harmless, you do not > need the go threads. Nonetheless, I think that the go run time should retry > instead of printing that trace. Cheers, mwh -- Snapcraft mailing list Snapcraft@lists.snapcraft.io Modify settings or unsubscribe at: https://lists.ubuntu.com/mailman/listinfo/snapcraft
