From mboxrd@z Thu Jan 1 00:00:00 1970 From: Li Zefan Subject: [PATCH 2/3] cgroup: fix umount vs cgroup_event_remove() race Date: Tue, 18 Jun 2013 18:41:10 +0800 Message-ID: <51C03946.5050707@huawei.com> References: <51C03913.5020008@huawei.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <51C03913.5020008@huawei.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" To: Tejun Heo Cc: LKML , Cgroups commit 5db9a4d99b0157a513944e9a44d29c9cec2e91dc Author: Tejun Heo Date: Sat Jul 7 16:08:18 2012 -0700 cgroup: fix cgroup hierarchy umount race This commit fixed a race caused by the dput() in css_dput_fn(), but the dput() in cgroup_event_remove() can also lead to the same BUG(). Signed-off-by: Li Zefan --- kernel/cgroup.c | 25 +++++++++++++++++++------ 1 file changed, 19 insertions(+), 6 deletions(-) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 482252a..e2dcf08 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -3812,6 +3812,23 @@ static int cgroup_write_notify_on_release(struct cgroup *cgrp, } /* + * When dput() is called asynchronously, if umount has been done and + * then deactivate_super() in cgroup_free_fn() kills the superblock, + * there's a small window that vfs will see the root dentry with non-zero + * refcnt and trigger BUG(). + * + * That's why we hold a reference before dput() and drop it right after. + */ +static void cgroup_dput(struct cgroup *cgrp) +{ + struct super_block *sb = cgrp->root->sb; + + atomic_inc(&sb->s_active); + dput(cgrp->dentry); + deactivate_super(sb); +} + +/* * Unregister event and free resources. * * Gets called from workqueue. @@ -3831,7 +3848,7 @@ static void cgroup_event_remove(struct work_struct *work) eventfd_ctx_put(event->eventfd); kfree(event); - dput(cgrp->dentry); + cgroup_dput(cgrp); } /* @@ -4119,12 +4136,8 @@ static void css_dput_fn(struct work_struct *work) { struct cgroup_subsys_state *css = container_of(work, struct cgroup_subsys_state, dput_work); - struct dentry *dentry = css->cgroup->dentry; - struct super_block *sb = dentry->d_sb; - atomic_inc(&sb->s_active); - dput(dentry); - deactivate_super(sb); + cgroup_dput(css->cgroup); } static void css_release(struct percpu_ref *ref) -- 1.8.0.2