From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Kirill A. Shutemov" <kirill-oKw7cIdHH8eLwutG50LtGA@public.gmane.org>
Subject: Re: [RFC] patch
Date: Mon, 2 Apr 2012 13:29:31 +0300
Message-ID: <20120402102931.GA5885@shutemov.name>
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To: Alexander Nikiforov <a.nikiforov-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>
Cc: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, KAMEZAWA Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>, Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>, Frederic Weisbecker <fweisbec-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>

On Mon, Apr 02, 2012 at 08:22:14AM +0400, Alexander Nikiforov wrote:

I think it should be part of task counter css, not core.
CC list updated.

> @@ -4558,6 +4594,22 @@ void cgroup_fork(struct task_struct *child)
>  	child->cgroups = current->cgroups;
>  	get_css_set(child->cgroups);
>  	INIT_LIST_HEAD(&child->cg_list);
> +
> +	struct cgroupfs_root *root;
> +
> +	/* send event to the userspace */
> +	mutex_lock(&cgroup_mutex);
> +	for_each_active_root(root) {
> +		struct cgroup *cgrp;
> +		struct fe_eventfd_list *ev;
> +
> +		cgrp = task_cgroup_from_root(child, root);
> +
> +		list_for_each_entry(ev, &cgrp->fe_notify, list) {
> +			eventfd_signal(ev->eventfd, 1);
> +		}
> +	}
> +	mutex_unlock(&cgroup_mutex);
>  }

How does it affect performance?

>  
>  /**
> @@ -4653,6 +4705,7 @@ void cgroup_exit(struct task_struct *tsk, int run_callbacks)
>  {
>  	struct css_set *cg;
>  	int i;
> +	struct cgroupfs_root *root;
>  
>  	/*
>  	 * Unlink from the css_set task list if necessary.
> @@ -4666,6 +4719,20 @@ void cgroup_exit(struct task_struct *tsk, int run_callbacks)
>  		write_unlock(&css_set_lock);
>  	}
>  
> +	/* send event to the userspace */
> +	mutex_lock(&cgroup_mutex);
> +	for_each_active_root(root) {
> +		struct cgroup *cgrp;
> +		struct fe_eventfd_list *ev;
> +
> +		cgrp = task_cgroup_from_root(tsk, root);
> +
> +		list_for_each_entry(ev, &cgrp->fe_notify, list) {
> +			eventfd_signal(ev->eventfd, 1);
> +		}
> +	}
> +	mutex_unlock(&cgroup_mutex);
> +

I think it's racy. You need to notify userspace after reassigning the
task, not before.

>  	/* Reassign the task to the init_css_set. */
>  	task_lock(tsk);
>  	cg = tsk->cgroups;


-- 
 Kirill A. Shutemov