It turns out that the WARN_ON_ONCE() call in css_release_work_fn
introduced by commit ab0312526867 ("cgroup: Show # of subsystem CSSes
in cgroup.stat") is incorrect. Although css->nr_descendants must be
0 when a css is released and ready to be freed, the corresponding
cgrp->nr_dying_subsys[ss->id] may not be 0 if a subsystem is activated
and deactivated multiple times with one or more of its previous
activation leaving behind dying csses.
Fix the incorrect warning by removing the cgrp->nr_dying_subsys check.
Fixes: ab0312526867 ("cgroup: Show # of subsystem CSSes in cgroup.stat")
Closes: https://lore.kernel.org/cgroups/6f301773-2fce-4602-a391-8af7ef00b2fb@xxxxxxxxxx/T/#t
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
---
kernel/cgroup/cgroup.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 601600afdd20..244ec600b4d8 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -5465,7 +5465,14 @@ static void css_release_work_fn(struct work_struct *work)
ss->css_released(css);
cgrp->nr_dying_subsys[ss->id]--;
- WARN_ON_ONCE(css->nr_descendants || cgrp->nr_dying_subsys[ss->id]);
+ /*
+ * When a css is released and ready to be freed, its
+ * nr_descendants must be zero. However, the corresponding
+ * cgrp->nr_dying_subsys[ss->id] may not be 0 if a subsystem
+ * is activated and deactivated multiple times with one or
+ * more of its previous activation leaving behind dying csses.
+ */
+ WARN_ON_ONCE(css->nr_descendants);
parent_cgrp = cgroup_parent(cgrp);
while (parent_cgrp) {
parent_cgrp->nr_dying_subsys[ss->id]--;
--
2.43.5
