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cgroup: implement cgroup_from_id()
This will be used as a replacement for css_lookup(). There's a difference with cgroup id and css id. cgroup id starts with 0, while css id starts with 1. v4: - also check if cggroup_mutex is held. - make it an inline function. Signed-off-by: Li Zefan <lizefan@huawei.com> Reviewed-by: Michal Hocko <mhocko@suse.cz> Signed-off-by: Tejun Heo <tj@kernel.org>
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@ -720,6 +720,24 @@ static inline struct cgroup* task_cgroup(struct task_struct *task,
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return task_subsys_state(task, subsys_id)->cgroup;
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}
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/**
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* cgroup_from_id - lookup cgroup by id
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* @ss: cgroup subsys to be looked into
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* @id: the cgroup id
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*
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* Returns the cgroup if there's valid one with @id, otherwise returns NULL.
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* Should be called under rcu_read_lock().
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*/
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static inline struct cgroup *cgroup_from_id(struct cgroup_subsys *ss, int id)
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{
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#ifdef CONFIG_PROVE_RCU
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rcu_lockdep_assert(rcu_read_lock_held() ||
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lockdep_is_held(&cgroup_mutex),
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"cgroup_from_id() needs proper protection");
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#endif
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return idr_find(&ss->root->cgroup_idr, id);
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}
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struct cgroup *cgroup_next_sibling(struct cgroup *pos);
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/**
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