Commit 6f30558f authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: make cgroup hold onto its kernfs_node 



cgroup currently releases its kernfs_node when it gets removed.  While
not buggy, this makes cgroup->kn access rules complicated than
necessary and leads to things like get/put protection around
kernfs_remove() in cgroup_destroy_locked().  In addition, we want to
use kernfs_name/path() and friends but also want to be able to
determine a cgroup's name between removal and release.

This patch makes cgroup hold onto its kernfs_node until freed so that
cgroup->kn is always accessible.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
parent 21a2d343

kernel/cgroup.c

+9 −7
Original line number Diff line number Diff line
@@ -957,6 +957,8 @@ static void cgroup_free_fn(struct work_struct *work) 


	cgroup_pidlist_destroy_all(cgrp);



	kernfs_put(cgrp->kn);



	kfree(rcu_dereference_raw(cgrp->name));

	kfree(cgrp);

}
@@ -3786,6 +3788,12 @@ static long cgroup_create(struct cgroup *parent, const char *name_str, 
	}

	cgrp->kn = kn;



	/*

	 * This extra ref will be put in cgroup_free_fn() and guarantees

	 * that @cgrp->kn is always accessible.

	 */

	kernfs_get(kn);



	cgrp->serial_nr = cgroup_serial_nr_next++;



	/* allocation complete, commit to creation */
@@ -3966,7 +3974,6 @@ static int cgroup_destroy_locked(struct cgroup *cgrp) 
{

	struct cgroup *child;

	struct cgroup_subsys_state *css;

	struct kernfs_node *kn;

	bool empty;

	int ssid;
@@ -4044,13 +4051,8 @@ static int cgroup_destroy_locked(struct cgroup *cgrp) 
	 * clearing of cgrp->kn->priv backpointer, which should happen

	 * after all files under it have been removed.

	 */

	kn = cgrp->kn;

	kernfs_get(kn);



	kernfs_remove(cgrp->kn);



	kernfs_remove(cgrp->kn);	/* @cgrp has an extra ref on its kn */

	RCU_INIT_POINTER(*(void __rcu __force **)&cgrp->kn->priv, NULL);

	kernfs_put(kn);



	mutex_lock(&cgroup_mutex);

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