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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>
wifi-calibration
Tejun Heo 2014-05-13 12:19:22 -04:00
parent ddab2b6e0e
commit cfc79d5bec
1 changed files with 12 additions and 11 deletions
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23
kernel/cgroup.c
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@ -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)