[Devel] [PATCH VZ8 v1 07/14] ve/cgroup: Added ve_owner field to cgroup

[Valeriy Vdovin]

Each cgroup representing a host or a container root of
cgroup subsystem hierarhy will have this field set to
a valid ve_struct, that owns this root. This way each
cgroup in a system will be able to know it's owning VE.
Non root cgroups will have this field set to NULL, this
is an optimization for cleanup code: at VE destruction
we only need to iterate over all root cgroups to clean
reference to former owning VE, rather than over all
cgroup hierarchy.
Still any cgroup that wants to know about it's owning
VE can find it's virtual root cgroup and read it's
ve_owner field.

cgroup->ve_owner is declared as RCU pointer, because it fits
RCU semantics - rare writes/often reads. ve_owner will be
read from multiple locations in code in further patches and
is only rarely set at cgroup_mark_ve_root/cgroup_mount.
cgroup_get_ve_owner is a read wrapper for this purpose.

(Cherry-picked from eb9c0bfae39fe336173a0dec11bc24f7275de3f8)
Signed-off-by: Valeriy Vdovin <valeriy.vdovin at virtuozzo.com>
---
 include/linux/cgroup-defs.h |  3 +++
 include/linux/cgroup.h      |  1 +
 kernel/cgroup/cgroup.c      | 44 +++++++++++++++++++++++++++++++++++++
 3 files changed, 48 insertions(+)

diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 4fd566414274..e497387872f4 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -528,6 +528,9 @@ struct cgroup {
 
 	u64 subgroups_limit;
 
+	/* ve_owner, responsible for running release agent. */
+	struct ve_struct __rcu *ve_owner;
+
 	/* ids of the ancestors at each level including self */
 	int ancestor_ids[];
 };
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index a1e6822bca8f..df9a9a09ce2a 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -900,6 +900,7 @@ int cgroup_path_ns(struct cgroup *cgrp, char *buf, size_t buflen,
 #ifdef CONFIG_VE
 extern void cgroup_mark_ve_root(struct ve_struct *ve);
 void cgroup_unmark_ve_roots(struct ve_struct *ve);
+struct ve_struct *cgroup_get_ve_owner(struct cgroup *cgrp);
 #endif
 
 #else /* !CONFIG_CGROUPS */
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 53a349539256..ff0a803c3aad 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -303,6 +303,43 @@ bool cgroup_on_dfl(const struct cgroup *cgrp)
 	return cgrp->root == &cgrp_dfl_root;
 }
 
+struct cgroup *cgroup_get_local_root(struct cgroup *cgrp)
+{
+	/*
+	 * Find nearest root cgroup, which might be host cgroup root
+	 * or ve cgroup root.
+	 *
+	 *    <host_root_cgroup> -> local_root
+	 *     \                    ^
+	 *      <cgroup>            |
+	 *       \                  |
+	 *        <cgroup>   --->   from here
+	 *        \
+	 *         <ve_root_cgroup> -> local_root
+	 *         \                   ^
+	 *          <cgroup>           |
+	 *          \                  |
+	 *           <cgroup>  --->    from here
+	 */
+
+	while (cgrp->kn->parent && !test_bit(CGRP_VE_ROOT, &cgrp->flags))
+		cgrp = cgrp->kn->parent->priv;
+
+	return cgrp;
+}
+
+struct ve_struct *cgroup_get_ve_owner(struct cgroup *cgrp)
+{
+	struct ve_struct *ve;
+	/* Caller should hold RCU */
+
+	cgrp = cgroup_get_local_root(cgrp);
+	ve = rcu_dereference(cgrp->ve_owner);
+	if (!ve)
+		ve = get_ve0();
+	return ve;
+}
+
 /* IDR wrappers which synchronize using cgroup_idr_lock */
 static int cgroup_idr_alloc(struct idr *idr, void *ptr, int start, int end,
 			    gfp_t gfp_mask)
@@ -1900,6 +1937,7 @@ void cgroup_mark_ve_root(struct ve_struct *ve)
 
 	list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
 		cgrp = link->cgrp;
+		rcu_assign_pointer(cgrp->ve_owner, ve);
 		set_bit(CGRP_VE_ROOT, &cgrp->flags);
 	}
 	link_ve_root_cpu_cgroup(cset->subsys[cpu_cgrp_id]);
@@ -1907,6 +1945,7 @@ void cgroup_mark_ve_root(struct ve_struct *ve)
 	rcu_read_unlock();
 
 	spin_unlock_irq(&css_set_lock);
+	synchronize_rcu();
 }
 
 void cgroup_unmark_ve_roots(struct ve_struct *ve)
@@ -1924,6 +1963,7 @@ void cgroup_unmark_ve_roots(struct ve_struct *ve)
 
 	list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
 		cgrp = link->cgrp;
+		rcu_assign_pointer(cgrp->ve_owner, NULL);
 		clear_bit(CGRP_VE_ROOT, &cgrp->flags);
 	}
 	link_ve_root_cpu_cgroup(cset->subsys[cpu_cgrp_id]);
@@ -1931,6 +1971,8 @@ void cgroup_unmark_ve_roots(struct ve_struct *ve)
 	rcu_read_unlock();
 
 	spin_unlock_irq(&css_set_lock);
+	/* ve_owner == NULL will be visible */
+	synchronize_rcu();
 }
 
 struct cgroup *cgroup_get_ve_root1(struct cgroup *cgrp)
@@ -2115,6 +2157,8 @@ struct dentry *cgroup_do_mount(struct file_system_type *fs_type, int flags,
 	struct dentry *dentry;
 	bool new_sb = false;
 
+	RCU_INIT_POINTER(root->cgrp.ve_owner, &ve0);
+
 	dentry = kernfs_mount(fs_type, flags, root->kf_root, magic, &new_sb);
 
 	/*
-- 
2.27.0