xref: /openbmc/linux/Documentation/trace/rv/monitor_wwnr.rst (revision c900529f3d9161bfde5cca0754f83b4d3c3e0220)

Monitor wwnr
============

- Name: wwrn - wakeup while not running
- Type: per-task deterministic automaton
- Author: Daniel Bristot de Oliveira <bristot@kernel.org>

Description
-----------

This is a per-task sample monitor, with the following
definition::

               |
               |
               v
    wakeup   +-------------+
  +--------- |             |
  |          | not_running |
  +--------> |             | <+
             +-------------+  |
               |              |
               | switch_in    | switch_out
               v              |
             +-------------+  |
             |   running   | -+
             +-------------+

This model is broken, the reason is that a task can be running
in the processor without being set as RUNNABLE. Think about a
task about to sleep::

  1:      set_current_state(TASK_UNINTERRUPTIBLE);
  2:      schedule();

And then imagine an IRQ happening in between the lines one and two,
waking the task up. BOOM, the wakeup will happen while the task is
running.

- Why do we need this model, so?
- To test the reactors.

Specification
-------------
Grapviz Dot file in tools/verification/models/wwnr.dot