[Devel] [PATCH RHEL7 v19 07/13] ve/cgroup: Added ve_owner field to cgroup

[Kirill Tkhai]

On 23.04.2020 18:44, Valeriy Vdovin wrote:
> 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.
> 
> Signed-off-by: Valeriy Vdovin <valeriy.vdovin at virtuozzo.com>

Reviewed-by: Kirill Tkhai <ktkhai at virtuozzo.com>

> ---
>  include/linux/cgroup.h |  4 ++++
>  kernel/cgroup.c        | 45 +++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 49 insertions(+)
> 
> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
> index 1bd0fe7..ad437a8 100644
> --- a/include/linux/cgroup.h
> +++ b/include/linux/cgroup.h
> @@ -292,6 +292,9 @@ struct cgroup {
>  	/* directory xattrs */
>  	struct simple_xattrs xattrs;
>  	u64 subgroups_limit;
> +
> +	/* ve_owner, responsible for running release agent. */
> +	struct ve_struct __rcu *ve_owner;
>  };
>  
>  #define MAX_CGROUP_ROOT_NAMELEN 64
> @@ -637,6 +640,7 @@ int cgroup_task_count(const struct cgroup *cgrp);
>  #ifdef CONFIG_VE
>  void cgroup_mark_ve_roots(struct ve_struct *ve);
>  void cgroup_unmark_ve_roots(struct ve_struct *ve);
> +struct ve_struct *cgroup_get_ve_owner(struct cgroup *cgrp);
>  #endif
>  
>  /*
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index 010a23e..c4e0126 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -805,6 +805,42 @@ static struct cgroup_name *cgroup_alloc_name(struct dentry *dentry)
>  	return name;
>  }
>  
> +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->parent && !test_bit(CGRP_VE_ROOT, &cgrp->flags))
> +		cgrp = cgrp->parent;
> +
> +	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;
> +}
> +
>  static void cgroup_free_fn(struct work_struct *work)
>  {
>  	struct cgroup *cgrp = container_of(work, struct cgroup, destroy_work);
> @@ -1627,6 +1663,8 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
>  		ret = PTR_ERR(new_root);
>  		goto drop_modules;
>  	}
> +
> +	RCU_INIT_POINTER(new_root->top_cgroup.ve_owner, &ve0);
>  	opts.new_root = new_root;
>  
>  	/* Locate an existing or new sb for this hierarchy */
> @@ -4254,12 +4292,14 @@ void cgroup_mark_ve_roots(struct ve_struct *ve)
>  	mutex_lock(&cgroup_mutex);
>  	for_each_active_root(root) {
>  		cgrp = task_cgroup_from_root(ve->init_task, root);
> +		rcu_assign_pointer(cgrp->ve_owner, ve);
>  		set_bit(CGRP_VE_ROOT, &cgrp->flags);
>  
>  		if (test_bit(cpu_cgroup_subsys_id, &root->subsys_mask))
>  			link_ve_root_cpu_cgroup(cgrp);
>  	}
>  	mutex_unlock(&cgroup_mutex);
> +	synchronize_rcu();
>  }
>  
>  void cgroup_unmark_ve_roots(struct ve_struct *ve)
> @@ -4270,9 +4310,14 @@ void cgroup_unmark_ve_roots(struct ve_struct *ve)
>  	mutex_lock(&cgroup_mutex);
>  	for_each_active_root(root) {
>  		cgrp = css_cgroup_from_root(ve->root_css_set, root);
> +		BUG_ON(!rcu_dereference_protected(cgrp->ve_owner,
> +				lockdep_is_held(&cgroup_mutex)));
> +		rcu_assign_pointer(cgrp->ve_owner, NULL);
>  		clear_bit(CGRP_VE_ROOT, &cgrp->flags);
>  	}
>  	mutex_unlock(&cgroup_mutex);
> +	/* ve_owner == NULL will be visible */
> +	synchronize_rcu();
>  }
>  
>  struct cgroup *cgroup_get_ve_root(struct cgroup *cgrp)
>