Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit cfc79d5b authored by Tejun Heo's avatar Tejun Heo
Browse files

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: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
parent ddab2b6e

kernel/cgroup.c

+12 −11
Original line number Diff line number Diff line
@@ -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)