diff options
| author | Li Zefan <lizefan@huawei.com> | 2013-06-18 18:41:10 +0800 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2013-07-21 18:21:25 -0700 |
| commit | 83d0eb79752482bb888fb6d86ceed8971272f8b4 (patch) | |
| tree | 626f556740e4aa16fb6bba39b28977b61a728cda | |
| parent | 5eb2698932989f855e3427b0860771611f831a69 (diff) | |
cgroup: fix umount vs cgroup_event_remove() race
commit 1c8158eeae0f37d0eee9f1fbe68080df6a408df2 upstream.
commit 5db9a4d99b0157a513944e9a44d29c9cec2e91dc
Author: Tejun Heo <tj@kernel.org>
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 <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | kernel/cgroup.c | 25 |
1 files changed, 19 insertions, 6 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c index a7c9e6ddb979..c6e77ef2a0a6 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -3727,6 +3727,23 @@ 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. @@ -3746,7 +3763,7 @@ static void cgroup_event_remove(struct work_struct *work) eventfd_ctx_put(event->eventfd); kfree(event); - dput(cgrp->dentry); + cgroup_dput(cgrp); } /* @@ -4031,12 +4048,8 @@ 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 init_cgroup_css(struct cgroup_subsys_state *css, |