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authorLi Zefan <lizefan@huawei.com>2013-06-18 18:41:10 +0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-07-21 18:21:25 -0700
commit83d0eb79752482bb888fb6d86ceed8971272f8b4 (patch)
tree626f556740e4aa16fb6bba39b28977b61a728cda /kernel/cgroup.c
parent5eb2698932989f855e3427b0860771611f831a69 (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>
Diffstat (limited to 'kernel/cgroup.c')
-rw-r--r--kernel/cgroup.c25
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,