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 <t...@kernel.org>
---
kernel/cgroup.c | 23 ++++++++++++-----------
1 file changed, 12 insertions(+), 11 deletions(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index f544e46..3118a63 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4547,17 +4547,7 @@ 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_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;
@@ -4616,6 +4606,17 @@ 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_from_dir(). Those are supported by RCU protecting
+ * clearing of 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;
}
@@ -5175,7 +5176,7 @@ struct cgroup_subsys_state *css_tryget_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)
--
1.9.0
--
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