[lttng-dev] [RFC PATCH v2 00/13] Sessiond teardown overhaul

[jonathan.rajotte-julien@efficios.com (Jonathan Rajotte)]

Hi,

This series objective is to review how the sessiond teardown is conducted. This is
the result of stress testing the teardown code path using [1] and the discussion
following previous proposed fixes [2][3].

The main problematic is that applications could hang on
application-initiated communication via the notify socket. This would end up
causing multiple deadlock scenarios where sessiond would wait on communications
for an already stuck application. This is caused by the absence of certain
threads at the moment the application is communicating and data handling race
during the teardown. I propose to impose a teardown order for thread to prevent
such issue.

The teardown mechanisms were revolving around the use of the
thread_quit_pipe. Most thread would listen on this pipe for the go signal of
termination. This result is a non-deterministic teardown code path and result in
scenarios quite hard to reproduce.

This series mostly introduce specialized quit pipes offering better control
over the lifetime of important/interdependent(data-wise) threads.

It also includes fixes to problems found along the way.

[1] https://github.com/PSRCode/lttng-stress
[2] https://lists.lttng.org/pipermail/lttng-dev/2017-August/027366.html
[3] https://lists.lttng.org/pipermail/lttng-dev/2017-August/027365.html