Move cgroup->sibling unlinking from cgroup_destroy_css_killed() to
cgroup_put(). This is later but still before the RCU grace period, so
it doesn't break css_next_child() although there now is a larger
window in which a dead cgroup is visible during css iteration. As css
iteration always could have included offline csses, this doesn't
affect correctness; however, it does make css_next_child() fall back
to reiterting mode more often. This also makes cgroup_put() directly
take cgroup_mutex, which limits where it can be called from. These
are not immediately problematic and will be dealt with later.
This change enables simplification of cgroup destruction path.
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
---
kernel/cgroup.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 45149b7..87ea2ce 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1056,6 +1056,11 @@ static void cgroup_put(struct cgroup *cgrp)
if (WARN_ON_ONCE(cgrp->parent && !cgroup_is_dead(cgrp)))
return;
+ /* delete this cgroup from parent->children */
+ mutex_lock(&cgroup_mutex);
+ list_del_rcu(&cgrp->sibling);
+ mutex_unlock(&cgroup_mutex);
+
cgroup_idr_remove(&cgrp->root->cgroup_idr, cgrp->id);
cgrp->id = -1;
@@ -4560,9 +4565,6 @@ static void cgroup_destroy_css_killed(struct cgroup *cgrp)
{
lockdep_assert_held(&cgroup_mutex);
- /* delete this cgroup from parent->children */
- list_del_rcu(&cgrp->sibling);
-
cgroup_put(cgrp);
}
--
1.9.0
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