cgroup_enable_threaded() checks that the cgroup doesn't have any tasks
or children and fails the operation if so. This test is unnecessary
because the first part is already checked by
cgroup_can_be_thread_root() and the latter is unnecessary. The latter
actually cause a behavioral oddity. Please consider the following
hierarchy. All cgroups are domains.
A
/ \
B C
\
D
If B is made threaded, C and D becomes invalid domains. Due to the no
children restriction, threaded mode can't be enabled on C. For C and
D, the only thing the user can do is removal.
There is no reason for this restriction. Remove it.
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Cc: Waiman Long <longman@xxxxxxxxxx>
---
Hello,
So, the only thing inconsistent there was the extra restriction when
enabling threaded mode when all the necessary conditions are already
checked by when verifying the parent's domain.
Thanks.
Documentation/cgroup-v2.txt | 5 +++--
kernel/cgroup/cgroup.c | 7 -------
2 files changed, 3 insertions(+), 9 deletions(-)
--- a/Documentation/cgroup-v2.txt
+++ b/Documentation/cgroup-v2.txt
@@ -274,8 +274,9 @@ thread mode, the following conditions mu
- As the cgroup will join the parent's resource domain. The parent
must either be a valid (threaded) domain or a threaded cgroup.
-- The cgroup must be empty. No enabled controllers, child cgroups or
- processes.
+- When the parent is an unthreaded domain, it must not have any domain
+ controllers enabled or populated domain children. The root is
+ exempt from this requirement.
Topology-wise, a cgroup can be in an invalid state. Please consider
the following toplogy::
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -3147,13 +3147,6 @@ static int cgroup_enable_threaded(struct
return -EOPNOTSUPP;
/*
- * Allow enabling thread mode only on empty cgroups to avoid
- * implicit migrations and recursive operations.
- */
- if (cgroup_has_tasks(cgrp) || css_has_online_children(&cgrp->self))
- return -EBUSY;
-
- /*
* The following shouldn't cause actual migrations and should
* always succeed.
*/
--
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