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| author | Hugh Dickins <hughd@google.com> | 2013-08-28 16:31:23 -0700 |
|---|---|---|
| committer | Tejun Heo <tj@kernel.org> | 2013-08-29 11:05:07 -0400 |
| commit | bb78a92f47696b2da49f2692b6a9fa56d07c444a (patch) | |
| tree | 6750776493dcfd0cd180b7fc0a666406708547c8 | |
| parent | c95389b4cd6a4b52af78bea706a274453e886251 (diff) | |
| download | linux-bb78a92f47696b2da49f2692b6a9fa56d07c444a.tar.gz linux-bb78a92f47696b2da49f2692b6a9fa56d07c444a.tar.xz | |
cgroup: fix rmdir EBUSY regression in 3.11
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 <hughd@google.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
| -rw-r--r-- | kernel/cgroup.c | 19 |
1 files changed, 18 insertions, 1 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 781845a013ab..e91963302c0d 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -4480,6 +4480,7 @@ 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); @@ -4490,12 +4491,28 @@ static int cgroup_destroy_locked(struct cgroup *cgrp) * @cgrp from being removed while __put_css_set() is in progress. */ read_lock(&css_set_lock); - empty = list_empty(&cgrp->cset_links) && list_empty(&cgrp->children); + empty = list_empty(&cgrp->cset_links); read_unlock(&css_set_lock); if (!empty) 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_dead(child); + if (!empty) + break; + } + rcu_read_unlock(); + if (!empty) + return -EBUSY; + + /* * Block new css_tryget() by killing css refcnts. cgroup core * guarantees that, by the time ->css_offline() is invoked, no new * css reference will be given out via css_tryget(). We can't |