cgroup: move cgroup->kn->priv clearing to cgroup_rmdir()

The ->priv field of a cgroup directory kernfs_node points back to the
cgroup.  This field is RCU cleared in cgroup_destroy_locked() for
non-kernfs accesses from css_tryget_from_dir() and
cgroupstats_build().

As these are only applicable to cgroups which finished creation
successfully and fully initialized cgroups are always removed by
cgroup_rmdir(), this can be safely moved to the end of cgroup_rmdir().

This will help simplifying cgroup locking and shouldn't introduce any
behavior difference.

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

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 8afddb1..b49e63d 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4546,17 +4546,7 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
 
        /* remove @cgrp directory along with the base files */
        mutex_unlock(&cgroup_mutex);
-
-       /*
-        * There are two control paths which try to determine cgroup from
-        * dentry without going through kernfs - cgroupstats_build() and
-        * css_tryget_online_from_dir().  Those are supported by RCU
-        * protecting clearing of cgrp->kn->priv backpointer, which should
-        * happen after all files under it have been removed.
-        */
        kernfs_remove(cgrp->kn);        /* @cgrp has an extra ref on its kn */
-       RCU_INIT_POINTER(*(void __rcu __force **)&cgrp->kn->priv, NULL);
-
        mutex_lock(&cgroup_mutex);
 
        return 0;
@@ -4615,6 +4605,17 @@ static int cgroup_rmdir(struct kernfs_node *kn)
        mutex_unlock(&cgroup_tree_mutex);
 
        kernfs_unbreak_active_protection(kn);
+
+       /*
+        * There are two control paths which try to determine cgroup from
+        * dentry without going through kernfs - cgroupstats_build() and
+        * css_tryget_online_from_dir().  Those are supported by RCU
+        * protecting clearing of cgrp->kn->priv backpointer, which should
+        * happen after all files under it have been removed.
+        */
+       if (!ret)
+               RCU_INIT_POINTER(*(void __rcu __force **)&kn->priv, NULL);
+
        cgroup_put(cgrp);
        return ret;
 }
@@ -5174,7 +5175,7 @@ struct cgroup_subsys_state *css_tryget_online_from_dir(struct dentry *dentry,
        /*
         * This path doesn't originate from kernfs and @kn could already
         * have been or be removed at any point.  @kn->priv is RCU
-        * protected for this access.  See destroy_locked() for details.
+        * protected for this access.  See cgroup_rmdir() for details.
         */
        cgrp = rcu_dereference(kn->priv);
        if (cgrp)