From mboxrd@z Thu Jan 1 00:00:00 1970 From: Li Zefan Subject: [PATCH stable-3.9] cgroup: fix umount vs cgroup_cfts_commit() race Date: Thu, 18 Jul 2013 11:08:31 +0800 Message-ID: <51E75C2F.1010408@huawei.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" To: Greg Kroah-Hartman Cc: Tejun Heo , Cgroups , stable 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 Signed-off-by: Tejun Heo [ 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