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cgroup: Fix incorrect WARN_ON_ONCE() in css_release_work_fn()

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It turns out that the WARN_ON_ONCE() call in css_release_work_fn
introduced by commit ab03125268 ("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: ab03125268 ("cgroup: Show # of subsystem CSSes in cgroup.stat")
Closes: https://lore.kernel.org/cgroups/6f301773-2fce-4602-a391-8af7ef00b2fb@redhat.com/T/#t
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Waiman Long 2024-08-08 23:22:59 -04:00 committed by Tejun Heo
parent 92841d6e23
commit 9b103943ab
1 changed files with 8 additions and 1 deletions
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9
kernel/cgroup/cgroup.c
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@ -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]--;