On Thu, Dec 5, 2013 at 7:15 AM, Stefan Hajnoczi <stefa...@gmail.com> wrote: > On Wed, Dec 04, 2013 at 11:21:12AM -0200, Eduardo Otubo wrote: >> On 12/04/2013 07:39 AM, Stefan Hajnoczi wrote: >> >On Fri, Nov 22, 2013 at 11:00:24AM -0500, Paul Moore wrote: >> >>>Developers will only be happy with seccomp if it's easy and rewarding to >> >>>support/debug. >> >> >> >>Agreed. >> >> >> >>As a developer, how do you feel about the audit/syslog based approach I >> >>mentioned earlier? >> > >> >I used the commands you posted (I think that's what you mean). They >> >produce useful output. >> > >> >The problem is that without an error message on stderr or from the >> >shell, no one will think "QEMU process dead and hung == check seccomp" >> >immediately. It's frustrating to deal with a "silent" failure. >> >> The process dies with a SIGKILL, and sig handling in Qemu is hard to >> implement due to dozen of external linked libraries that has their >> own signal masks and conflicts with seccomp. I've already tried this >> approach in the past (you can find in the list by searching for >> debug mode) > > I now realize we may be talking past each other. Dying with > SIGKILL/SIGSYS is perfectly reasonable and I would be happy with that > :-). > > But I think there's a bug in seccomp: a multi-threaded process can be > left in a zombie state. In my case the primary thread was killed by > seccomp but another thread was deadlocked on a futex. > > The result is the process isn't quite dead yet. The shell will not reap > it and we're stuck with a zombie. > > I can reproduce it reliably when I run "qemu-system-x86_64 -sandbox on" > on Fedora 20 (qemu-system-x86-1.6.1-2). > > Should seccomp use do_group_exit() for SIGKILL?
Is the problem that the SECCOMP_RET_KILL didn't take down the thread group (which would be a departure from how seccomp(mode=1) worked) and causes the deadlock somehow, or is it that the other thread is deadlocked? Regardless, adding a SECCOMP_RET_TGKILL probably isn't a bad idea :) cheers! will
