Re: [PATCH 1/5 V3] cgroup: remove redundate get/put of old css_set from migrate

[Li Zefan <lizf-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org>]

Mandeep Singh Baines wrote:
> Changes in V3:
> * Fixed to put error in retval (thanks Frederic Weisbecker)
>   * https://lkml.org/lkml/2011/12/20/255
> Changes in V2:
> * Updated commit message as per Tejun's feedback:
>   * https://lkml.org/lkml/2011/12/19/289
> 
> -- >8 -- (snip)
> 
> We can now assume that the css_set reference held by the task
> will not go away for an exiting task. PF_EXITING state can be
> trusted throughout migration by checking it after locking
> threadgroup.
> 
> While at it, renamed css_set_check_fetched to css_set_fetched.
> !css_set_fetched() seems to read better than
> !css_set_check_fetched().
> 
> Signed-off-by: Mandeep Singh Baines <msb-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>
> Cc: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
> Cc: Li Zefan <lizf-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org>
> Cc: containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org
> Cc: cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>
> Cc: Frederic Weisbecker <fweisbec-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> Cc: Oleg Nesterov <oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> Cc: Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
> Cc: Paul Menage <paul-inf54ven1CmVyaH7bEyXVA@public.gmane.org>
> ---
>  kernel/cgroup.c |   25 ++++++-------------------
>  1 files changed, 6 insertions(+), 19 deletions(-)
> 
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index bc3caff..4166066 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -1856,7 +1856,6 @@ static int cgroup_task_migrate(struct cgroup *cgrp, struct cgroup *oldcgrp,
>  	 */
>  	task_lock(tsk);

The comments above this line of code should be updated accordingly.

>  	oldcg = tsk->cgroups;
> -	get_css_set(oldcg);
>  	task_unlock(tsk);
>  
>  	/* locate or allocate a new css_set for this task. */