tree 050c706ba57986c93f1606314e969147ad921838
parent c8cbeac2cada1032ba5f585956f818d671cbcc65
author Shawn McCarney <shawnmm@us.ibm.com> 1631639556 -0500
committer Shawn McCarney <shawnmm@us.ibm.com> 1631651576 +0000

regulators: Fix race condition in monitor disable

There is a systemd service file that disables regulator monitoring when
the chassis is powered off.  This is necessary because we do not want to
read sensor values or check for phase faults when the chassis is powered
off.  Monitoring needs to stop before the regulators are disabled/turned
off.

The service file currently does not specify a 'Type', which means that
it defaults to Type 'simple'.  Service files of this Type are considered
started when they fork the specified executable.  That is, systemd does
not wait for the executable to complete.

In this case, we need the executable to complete.  The service runs the
regsctl executable, which makes a D-Bus method call to the regulators
application disabling monitoring.  We need this D-Bus method to complete
before proceeding with the power off.

Otherwise there is a race condition between the following:
* The timers that initiate sensor and phase fault monitoring could
  expire, causing unwanted monitoring to occur during power off.
* The regsctl executable could complete the D-Bus call, stopping
  monitoring and the associated timers.

The solution is to set the Type of the service file to 'oneshot'.  This
causes systemd to wait until the executable completes.

Signed-off-by: Shawn McCarney <shawnmm@us.ibm.com>
Change-Id: I399a2a4ba7f1a256c42a7e9b8b036abd1b077033