cgroup: fix locking in cgroupstats_build()

css_set_lock has been converted to css_set_rwsem, and rwsem can't nest
inside rcu_read_lock.

Signed-off-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 15dcae74b51061028cfffdc1eb63ebdd3d964733..5606c0f08d95c1da85f75b1326f99cfc81e053eb 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2995,6 +2995,8 @@ int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
            kernfs_type(kn) != KERNFS_DIR)
                return -EINVAL;
 
+       mutex_lock(&cgroup_mutex);
+
        /*
         * We aren't being called from kernfs and there's no guarantee on
         * @kn->priv's validity.  For this and css_tryget_from_dir(),
@@ -3002,10 +3004,12 @@ int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
         */
        rcu_read_lock();
        cgrp = rcu_dereference(kn->priv);
-       if (!cgrp) {
+       if (!cgrp || cgroup_is_dead(cgrp)) {
                rcu_read_unlock();
+               mutex_unlock(&cgroup_mutex);
                return -ENOENT;
        }
+       rcu_read_unlock();
 
        css_task_iter_start(&cgrp->dummy_css, &it);
        while ((tsk = css_task_iter_next(&it))) {
@@ -3030,7 +3034,7 @@ int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
        }
        css_task_iter_end(&it);
 
-       rcu_read_unlock();
+       mutex_unlock(&cgroup_mutex);
        return 0;
 }