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