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    SubjectRe: [PATCH 3/8] cgroup: add function to get task's cgroup
    Hello,

    On Mon, Nov 16, 2015 at 01:51:40PM -0600, serge@hallyn.com wrote:
    > diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
    > index 22e3754..29f0b02 100644
    > --- a/include/linux/cgroup.h
    > +++ b/include/linux/cgroup.h
    > @@ -326,6 +326,7 @@ static inline bool css_tryget_online(struct cgroup_subsys_state *css)
    > return percpu_ref_tryget_live(&css->refcnt);
    > return true;
    > }
    > +struct cgroup *get_task_cgroup(struct task_struct *task);

    Please move this where other prototypes are.

    > +/*
    > + * 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);
    > + spin_lock_bh(&css_set_lock);
    > +
    > + cgrp = task_cgroup_from_root(task, &cgrp_dfl_root);
    > + cgroup_get(cgrp);
    > +
    > + spin_unlock_bh(&css_set_lock);
    > + mutex_unlock(&cgroup_mutex);
    > + return cgrp;
    > +}
    > +EXPORT_SYMBOL_GPL(get_task_cgroup);

    So, exposing cgroup_mutex this way can lead to ugly lock dependency
    issues as cgroup_mutex is expected to be outside of pretty much
    everything. task_cgroup_path() does it but it has no users (should
    prolly removed) and cgroup_attach_task_all() is pretty specific.

    Hmmm... cc'ing Li (btw, please cc him and Johannes from the next
    posting). Li, I don't think cset_cgroup_from_root() really needs
    cgroup_mutex. css_set_lock seems to be enough. What do you think?

    Thanks.

    --
    tejun


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