[PATCH 1/3] cgroup: simplify double-check locking in cgroup_attach_proc

[Li Zefan]

Mandeep Singh Baines wrote:
> To keep the complexity of the double-check locking in one place,
> I moved the thread_group_leader check up into attach_task_by_pid.
> This allows us to use a goto instead of returning -EAGAIN.
> 
> While at it, converted a couple of returns to gotos and used
> rcu for the !pid case also in order to simplify the logic.
> 
> Changes in V2:
> * https://lkml.org/lkml/2011/12/22/86 (Tejun Heo)
>   * Use a goto instead of returning -EAGAIN
> 
> Signed-off-by: Mandeep Singh Baines <msb at chromium.org>

Acked-by: Li Zefan <lizf at cn.fujitsu.com>

> Cc: Tejun Heo <tj at kernel.org>
> Cc: Li Zefan <lizf at cn.fujitsu.com>
> Cc: Frederic Weisbecker <fweisbec at gmail.com>
> Cc: containers at lists.linux-foundation.org
> Cc: cgroups at vger.kernel.org
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu at jp.fujitsu.com>
> Cc: Oleg Nesterov <oleg at redhat.com>
> Cc: Andrew Morton <akpm at linux-foundation.org>
> Cc: Paul Menage <paul at paulmenage.org>
> ---
>  kernel/cgroup.c |   79 ++++++++++++++++++++----------------------------------
>  1 files changed, 29 insertions(+), 50 deletions(-)