Hello Tejun,
Suppose we have the following scenario:
x [d] (pids)
y [dt] (pids)
p [t]
q [t]
r [t]
z [d]
Here, x/y is a "domain threaded root" with a threaded controller
(the 'pids' controller) enabled. (In this scenario, there are no
member processes in any of the cgroups.)
Suppose we now convert x/z to "threaded" type:
# echo threaded > x/z/cgroup.type
Now we end up in the following state:
x [dt] (pids)
y [inv] (pids)
p [t]
q [t]
r [t]
z [t]
This seems odd. x/y is now of "domain invalid" type with a controller
enabled! This feels like a violation of the rules, since we can't
in other circumstances do anything with a "domain invalid" cgroup
except convert it to "threaded". In particular, we can't create
child cgroups under a "domain invalid" cgroup, or add member processes
to the cgroup, or *enable controllers in the cgroup*. In fact, when
doing the
# echo threaded > x/z/cgroup.type
I had expected a write(2) error because the state of x/y should
(I thought) not be permitted.
Your thoughts?
Thanks,
Michael
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
