Re: [PATCH -mmotm 2/4] cgroups: remove events before destroying subsystem state objects

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Sat, 20 Feb 2010 00:28:17 +0200
"Kirill A. Shutemov" <kirill@shutemov.name> wrote:

> Events should be removed after rmdir of cgroup directory, but before
> destroying subsystem state objects. Let's take reference to cgroup
> directory dentry to do that.
> 
> Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>

Okay, I welcome this.

Acked-by: KAMEZAWA Hiroyuki <kamezawa.hioryu@jp.fujitsu.com>

Just a quesion...After this change, if cgroup has remaining event,
cgroup is removed by workqueue of event->remove() -> d_put(), finally. Right ?
Do you have a test set for checking this behavior ?

Thanks,
-Kame



> ---
>  include/linux/cgroup.h |    3 ---
>  kernel/cgroup.c        |    8 ++++++++
>  mm/memcontrol.c        |    9 ---------
>  3 files changed, 8 insertions(+), 12 deletions(-)
> 
> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
> index 64cebfe..1719c75 100644
> --- a/include/linux/cgroup.h
> +++ b/include/linux/cgroup.h
> @@ -395,9 +395,6 @@ struct cftype {
>  	 * closes the eventfd or on cgroup removing.
>  	 * This callback must be implemented, if you want provide
>  	 * notification functionality.
> -	 *
> -	 * Be careful. It can be called after destroy(), so you have
> -	 * to keep all nesessary data, until all events are removed.
>  	 */
>  	int (*unregister_event)(struct cgroup *cgrp, struct cftype *cft,
>  			struct eventfd_ctx *eventfd);
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index 46903cb..d142524 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -2979,6 +2979,7 @@ static void cgroup_event_remove(struct work_struct *work)
>  
>  	eventfd_ctx_put(event->eventfd);
>  	kfree(event);
> +	dput(cgrp->dentry);
>  }
>  
>  /*
> @@ -3099,6 +3100,13 @@ static int cgroup_write_event_control(struct cgroup *cgrp, struct cftype *cft,
>  		goto fail;
>  	}
>  
> +	/*
> +	 * Events should be removed after rmdir of cgroup directory, but before
> +	 * destroying subsystem state objects. Let's take reference to cgroup
> +	 * directory dentry to do that.
> +	 */
> +	dget(cgrp->dentry);
> +
>  	spin_lock(&cgrp->event_list_lock);
>  	list_add(&event->list, &cgrp->event_list);
>  	spin_unlock(&cgrp->event_list_lock);
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index a443c30..8fe6e7f 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3358,12 +3358,6 @@ static int mem_cgroup_register_event(struct cgroup *cgrp, struct cftype *cft,
>  		}
>  	}
>  
> -	/*
> -	 * We need to increment refcnt to be sure that all thresholds
> -	 * will be unregistered before calling __mem_cgroup_free()
> -	 */
> -	mem_cgroup_get(memcg);
> -
>  	if (type == _MEM)
>  		rcu_assign_pointer(memcg->thresholds, thresholds_new);
>  	else
> @@ -3457,9 +3451,6 @@ assign:
>  	/* To be sure that nobody uses thresholds before freeing it */
>  	synchronize_rcu();
>  
> -	for (i = 0; i < thresholds->size - size; i++)
> -		mem_cgroup_put(memcg);
> -
>  	kfree(thresholds);
>  unlock:
>  	mutex_unlock(&memcg->thresholds_lock);
> -- 
> 1.6.6.2
> 
> 

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