From: Hugh Dickins <hu...@google.com>
commit bb78a92f47696b2da49f2692b6a9fa56d07c444a upstream.
On 3.11-rc we are seeing cgroup directories left behind when they should
have been removed. Here's a trivial reproducer:
cd /sys/fs/cgroup/memory
mkdir parent parent/child; rmdir parent/child parent
rmdir: failed to remove `parent': Device or resource busy
It's because cgroup_destroy_locked() (step 1 of destruction) leaves
cgroup on parent's children list, letting cgroup_offline_fn() (step 2 of
destruction) remove it; but step 2 is run by work queue, which may not
yet have removed the children when parent destruction checks the list.
Fix that by checking through a non-empty list of children: if every one
of them has already been marked CGRP_DEAD, then it's safe to proceed:
those children are invisible to userspace, and should not obstruct rmdir.
(I didn't see any reason to keep the cgrp->children checks under the
unrelated css_set_lock, so moved them out.)
tj: Flattened nested ifs a bit and updated comment so that it's
correct on both for-3.11-fixes and for-3.12.
Signed-off-by: Hugh Dickins <hu...@google.com>
Signed-off-by: Tejun Heo <t...@kernel.org>
https://jira.sw.ru/browse/PSBM-53314
[aryabinin: s/cgroup_is_dead()/cgroup_is_removed()]
Signed-off-by: Andrey Ryabinin <aryabi...@virtuozzo.com>
---
kernel/cgroup.c | 20 +++++++++++++++++++-
1 file changed, 19 insertions(+), 1 deletion(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 1c047b9..6aafc51 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4432,11 +4432,29 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
struct dentry *d = cgrp->dentry;
struct cgroup_event *event, *tmp;
struct cgroup_subsys *ss;
+ struct cgroup *child;
+ bool empty;
lockdep_assert_held(&d->d_inode->i_mutex);
lockdep_assert_held(&cgroup_mutex);
- if (atomic_read(&cgrp->count) || !list_empty(&cgrp->children))
+ if (atomic_read(&cgrp->count))
+ return -EBUSY;
+
+ /*
+ * Make sure there's no live children. We can't test ->children
+ * emptiness as dead children linger on it while being destroyed;
+ * otherwise, "rmdir parent/child parent" may fail with -EBUSY.
+ */
+ empty = true;
+ rcu_read_lock();
+ list_for_each_entry_rcu(child, &cgrp->children, sibling) {
+ empty = cgroup_is_removed(child);
+ if (!empty)
+ break;
+ }
+ rcu_read_unlock();
+ if (!empty)
return -EBUSY;
/*
--
2.10.2
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