CTDB: simple/90_debug_hung_script.sh test fails on some machines

Martin Schwenke martin at meltin.net
Wed Nov 14 04:04:26 UTC 2018

Hi Andrew,

On Wed, 14 Nov 2018 14:45:08 +1300, Andrew Bartlett
<abartlet at samba.org> wrote:

> On Wed, 2018-11-14 at 14:24 +1300, Tim Beale via samba-technical wrote:

> > I noticed a problem trying to run the samba_build_ctdb test on the
> > rackspace machines. The tests/simple/90_debug_hung_script.sh test-case
> > seems to reliably fail.
> > 
> > I could reproduce the failure by running the ctdb autobuild on my PC.
> > Basically the test is failing because the 'cat "/proc/${pid}/stack"' in
> > debug-hung-script.sh fails (Operation not permitted). The reason for the
> > failure seems to be the Yama ptrace_scope setting on the host machine.
> > https://www.kernel.org/doc/Documentation/security/Yama.txt
> > 
> > My PC had kernel.yama.ptrace_scope set to 1. If I set it to zero, then
> > the CTDB test passes. It seems like the gitlab CI machines must use a
> > ptrace_scope=0 setting.  

> Specifically, while the 'shared' runners must have a more liberal
> setting (as they pass), runners started by the Samba Team at Rackspace
> use a different kernel-side configuration.  
> We are testing out using Rackspace runners for the whole CI to ensure
> we don't strictly rely on the shared resources (which are free - to us
> - small VMs only available because we are on gitlab.com).
> While we are also looking to change that the ptrace limitations on
> 'our' machines, in the meantime it would be nice if the test was a
> little more accepting. 

I've attached a patch that attempts to work around this nonsense.  It
seems to work, but I think we need to do some more thinking before
pushing this fragile pile of toothpicks and snot.  :-D

We keep coming unstuck in this genre of tests, which attempt to check
whether our hung event script debugging works properly.   We've seen a
bug in pstree (that *usually* only manifests on very loaded test
systems) and now this, which is basically arbitrary "breakage by design"
in /proc/.

We might need a new approach.  I have some ideas... none of them
good...  yet...  :-(

Give me a little while... I'll also see if Amitay has any good idea...  :-)

peace & happiness,
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