[PATCHv1 3/8] cgroup: add function to get task's cgroup on default hierarchy

[Serge E. Hallyn]

Quoting Aditya Kali (adityakali at google.com):
> get_task_cgroup() returns the (reference counted) cgroup of the
> given task on the default hierarchy.
> 
> Signed-off-by: Aditya Kali <adityakali at google.com>

Acked-by: Serge Hallyn <serge.hallyn at canonical.com>

> ---
>  include/linux/cgroup.h |  1 +
>  kernel/cgroup.c        | 25 +++++++++++++++++++++++++
>  2 files changed, 26 insertions(+)
> 
> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
> index 1d51968..80ed6e0 100644
> --- a/include/linux/cgroup.h
> +++ b/include/linux/cgroup.h
> @@ -579,6 +579,7 @@ static inline void pr_cont_cgroup_path(struct cgroup *cgrp)
>  }
>  
>  char *task_cgroup_path(struct task_struct *task, char *buf, size_t buflen);
> +struct cgroup *get_task_cgroup(struct task_struct *task);
>  
>  int cgroup_add_dfl_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);
>  int cgroup_add_legacy_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index cab7dc4..56d507b 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -1916,6 +1916,31 @@ char *task_cgroup_path(struct task_struct *task, char *buf, size_t buflen)
>  }
>  EXPORT_SYMBOL_GPL(task_cgroup_path);
>  
> +/*
> + * get_task_cgroup - returns the cgroup of the task in the default cgroup
> + * hierarchy.
> + *
> + * @task: target task
> + * This function returns the @task's cgroup on the default cgroup hierarchy. The
> + * returned cgroup has its reference incremented (by calling cgroup_get()). So
> + * the caller must cgroup_put() the obtained reference once it is done with it.
> + */
> +struct cgroup *get_task_cgroup(struct task_struct *task)
> +{
> +	struct cgroup *cgrp;
> +
> +	mutex_lock(&cgroup_mutex);
> +	down_read(&css_set_rwsem);
> +
> +	cgrp = task_cgroup_from_root(task, &cgrp_dfl_root);
> +	cgroup_get(cgrp);
> +
> +	up_read(&css_set_rwsem);
> +	mutex_unlock(&cgroup_mutex);
> +	return cgrp;
> +}
> +EXPORT_SYMBOL_GPL(get_task_cgroup);
> +
>  /* used to track tasks and other necessary states during migration */
>  struct cgroup_taskset {
>  	/* the src and dst cset list running through cset->mg_node */
> -- 
> 2.1.0.rc2.206.gedb03e5
> 
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