[ltt-dev] UST: pending debugging

[Mathieu Desnoyers]

Hi Nils,

Yannick created a test case stress-testing forks with UST, and it seems we
need to do some debugging before a release.

git://git.dorsal.polymtl.ca/~ybrosseau/ust.git forkmany branch
tests/forkmany

Problem 1:
If we don't set ulimit -n to very high value, we bust the number of file
descriptors (1024) in the "flat fork" test (it starts failing around
60 forks on my machine). This shows that the consumer threads seem to
keep 2 file descriptors open per core per process, event after the
processes have exited. It's not timing related, as I tried adding
sleep(1) in there. The consumer thread loop seems to exit cleanly, but
for some reason the file descriptors are still open (probably).

Problem 2:
Yannick experienced a crash due to open_buffers_list corruption. I
expect that we are lacking some list protection (locking) in both init()
and destructor of libust (race between listener thread, fork, init and
destructor). I would like to serialize all these operations with the
listener_thread_data_mutex.

So I'm sending these leftover bugs to you, because I have gone way
beyond the time I can allocate to UST debugging at the moment.

We need many more stress tests like this.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com