| From | Greg Kroah-Hartman <> | Subject | [ 19/72] cgroup: fix umount vs cgroup_event_remove() race | Date | Thu, 18 Jul 2013 22:25:36 -0700 |
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3.10-stable review patch. If anyone has any objections, please let me know.
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From: Li Zefan <lizefan@huawei.com>
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>
--- kernel/cgroup.c | 25 +++++++++++++++++++------ 1 file changed, 19 insertions(+), 6 deletions(-)
--- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -3727,6 +3727,23 @@ static int cgroup_write_notify_on_releas } /* + * 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 w eventfd_ctx_put(event->eventfd); kfree(event); - dput(cgrp->dentry); + cgroup_dput(cgrp); } /* @@ -4031,12 +4048,8 @@ static void css_dput_fn(struct work_stru { 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,
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