commit 084457f284abf6789d90509ee11dae383842b23b upstream.
cgroup_cfts_commit() uses dget() to keep cgroup alive after cgroup_mutex
is dropped, but dget() won't prevent cgroupfs from being umounted. When
the race happens, vfs will see some dentries with non-zero refcnt while
umount is in process.
Keep running this:
mount -t cgroup -o blkio xxx /cgroup
umount /cgroup
And this:
modprobe cfq-iosched
rmmod cfs-iosched
After a while, the BUG() in shrink_dcache_for_umount_subtree() may
be triggered:
BUG: Dentry xxx{i=0,n=blkio.yyy} still in use (1) [umount of cgroup cgroup]
Signed-off-by: Li Zefan <lizefan@xxxxxxxxxx>
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
[ backported to 3.9:
- fixed build error: added '&' to atomic_inc_not_zero parameter;
this was fixed upstream by commit e8c82d20a9f729cf4b9f73043f7fd4e0872bebfd ]
---
kernel/cgroup.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index a32f943..1c98235 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2810,13 +2810,17 @@ static void cgroup_cfts_commit(struct cgroup_subsys *ss,
{
LIST_HEAD(pending);
struct cgroup *cgrp, *n;
+ struct super_block *sb = ss->root->sb;
/* %NULL @cfts indicates abort and don't bother if @ss isn't attached */
- if (cfts && ss->root != &rootnode) {
+ if (cfts && ss->root != &rootnode &&
+ atomic_inc_not_zero(&sb->s_active)) {
list_for_each_entry(cgrp, &ss->root->allcg_list, allcg_node) {
dget(cgrp->dentry);
list_add_tail(&cgrp->cft_q_node, &pending);
}
+ } else {
+ sb = NULL;
}
mutex_unlock(&cgroup_mutex);
@@ -2839,6 +2843,9 @@ static void cgroup_cfts_commit(struct cgroup_subsys *ss,
dput(cgrp->dentry);
}
+ if (sb)
+ deactivate_super(sb);
+
mutex_unlock(&cgroup_cft_mutex);
}
--
1.8.0.2
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