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cgroup: make cgroup hold onto its kernfs_node

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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: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
This commit is contained in:
Tejun Heo 2014-02-12 09:29:50 -05:00
parent 21a2d3430b
commit 6f30558f37
1 changed files with 9 additions and 7 deletions
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16
kernel/cgroup.c
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@ -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);