CC: Tejun

于 2013/2/6 23:16, Maxim Uvarov wrote:
> linux-3.0.y has put_css_set a litte bit down in the code,
> this should not be duplicated.

Why do you want to make this change? Have you encountered some kernel bug that 
relates
to cgroup?

> Signed-off-by: Maxim Uvarov <[email protected]>

NAck

> ---
>  kernel/cgroup.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index 1749dcd..2a08524 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -1777,7 +1777,6 @@ static int cgroup_task_migrate(struct cgroup *cgrp, 
> struct cgroup *oldcgrp,
>                       return -ENOMEM;
>               }
>       }
> -     put_css_set(oldcg);

This put_css_set() is paired with the code a little above:

        task_lock(tsk);
        oldcg = tsk->cgroups;
        get_css_set(oldcg);
        task_unlock(tsk);

It was added by this commit:

commit 77efecd9e0526327548152df715ab8644ecb5ba0
Author: Lai Jiangshan <[email protected]>
Date:   Wed Jan 7 18:07:39 2009 -0800

    cgroups: call find_css_set() safely in cgroup_attach_task()

And the put_css_set() at the end of this function is to really drop the ref to 
tsk->cgroups,
as tsk->cgroups will point to @newcg, so @oldcg should be de-referenced.

But yeah the comment above the second put_css_set() is confusing:

/*
 * We just gained a reference on oldcg by taking it from the task ...
 * ...
 */

I'll fix the comment for mainline.

>  
>       /* if PF_EXITING is set, the tsk->cgroups pointer is no longer safe. */
>       task_lock(tsk);
> 

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