[lldb-dev] The lit test driver gets killed because of SIGHUP

Zachary Turner via lldb-dev lldb-dev at lists.llvm.org
Tue Dec 4 19:10:50 PST 2018

Have you tried an strace to see if it tells you who is sending the signal?
On Tue, Dec 4, 2018 at 6:49 PM Jonas Devlieghere via lldb-dev <
lldb-dev at lists.llvm.org> wrote:

> Hi everyone,
> Since we switched to lit as the test driver we've been seeing it getting
> killed as the result of a SIGHUP signal. The problem doesn't reproduce on
> every machine and there seems to be a correlation between number of
> occurrences and thread count.
> Davide and Raphael spent some time narrowing down what particular test is
> causing this and it seems that TestChangeProcessGroup.py is always
> involved. However it never reproduces when running just this test. I was
> able to reproduce pretty consistently with the following filter:
> ./bin/llvm-lit ../llvm/tools/lldb/lit/Suite/ --filter="process"
> Bisecting the test itself didn't help much, the problem reproduces as soon
> as we attach to the inferior.
> At this point it is still not clear who is sending the SIGHUP and why it's
> reaching the lit test driver. Fred suggested that it might have something
> to do with process groups (which would be an interesting coincidence given
> the previously mentioned test) and he suggested having the test run in
> different process groups. Indeed, adding a call to os.setpgrp() in lit's
> executeCommand and having a different process group per test prevent us
> from seeing this. Regardless of this issue I think it's reasonable to have
> tests run in their process group, so if nobody objects I propose adding
> this to lit in llvm.
> Still, I'd like to understand where the signal is coming from and fix the
> root cause in addition to the symptom. Maybe someone here has an idea of
> what might be going on?
> Thanks,
> Jonas
> PS
> 1. There's two places where we send a SIGHUP ourself, with that code
> removed we still receive the signal, which suggests that it might be coming
> from Python or the OS.
> 2. If you're able to reproduce you'll see that adding an early return
> before the attach in TestChangeProcessGroup.py hides/prevents the problem.
> Moving the return down one line and it pops up again.
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