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    SubjectRe: [PATCH 05/12] blkcg: update blkg get functions take blkio_cgroup as parameter
    On Wed, Jan 18, 2012 at 05:11:23PM -0800, Tejun Heo wrote:

    [..]
    > -static struct throtl_grp * throtl_get_tg(struct throtl_data *td)
    > +static struct throtl_grp *throtl_get_tg(struct throtl_data *td,
    > + struct blkio_cgroup *blkcg)
    > {
    > struct throtl_grp *tg = NULL, *__tg = NULL;
    > - struct blkio_cgroup *blkcg;
    > struct request_queue *q = td->queue;
    >
    > /* no throttling for dead queue */
    > if (unlikely(blk_queue_dead(q)))
    > return NULL;
    >
    > - blkcg = task_blkio_cgroup(current);
    > tg = throtl_find_tg(td, blkcg);
    > if (tg)
    > return tg;
    >
    > + if (!css_tryget(&blkcg->css))
    > + return NULL;
    > +

    This reference is to make sure that blkcg does not go away while we drop
    the rcu lock and do the group allocation?

    Thanks
    Vivek


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