cgroup_destroy_locked() currently tests whether any css_sets are
associated to reject removal if the cgroup contains tasks. This works
because a css_set's refcnt converges with the number of tasks linked
to it and thus there's no css_set linked to a cgroup if it doesn't
have any live tasks.
To help tracking resource usage of zombie tasks, putting the ref of
css_set will be separated from disassociating the task from the
css_set which means that a cgroup may have css_sets linked to it even
when it doesn't have any live tasks.
This patch updates cgroup_destroy_locked() so that it tests
cgroup_is_populated(), which counts the number of populated css_sets,
instead of whether cgrp->cset_links is empty to determine whether the
cgroup is populated or not. This ensures that rmdirs won't be
incorrectly rejected for cgroups which only contain zombie tasks.
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
---
kernel/cgroup.c | 11 +++++------
1 file changed, 5 insertions(+), 6 deletions(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index ba11496..b8da97a 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4996,16 +4996,15 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
__releases(&cgroup_mutex) __acquires(&cgroup_mutex)
{
struct cgroup_subsys_state *css;
- bool empty;
int ssid;
lockdep_assert_held(&cgroup_mutex);
- /* css_set_rwsem synchronizes access to ->cset_links */
- down_read(&css_set_rwsem);
- empty = list_empty(&cgrp->cset_links);
- up_read(&css_set_rwsem);
- if (!empty)
+ /*
+ * Only migration can raise populated from zero and we're already
+ * holding cgroup_mutex.
+ */
+ if (cgroup_is_populated(cgrp))
return -EBUSY;
/*
--
2.4.3
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