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    SubjectRe: [PATCH block/for-3.4/core] cfq: fix cfqg ref handling when BLK_CGROUP && !CFQ_GROUP_IOSCHED
    On Thu, Mar 15, 2012 at 09:50:57AM -0700, Tejun Heo wrote:

    > > [..]
    > > > @@ -3533,7 +3551,7 @@ static int cfq_init_queue(struct request
    > > >
    > > > spin_lock_irq(q->queue_lock);
    > > > cfq_link_cfqq_cfqg(&cfqd->oom_cfqq, cfqd->root_group);
    > > > - blkg_put(cfqg_to_blkg(cfqd->root_group));
    > > > + cfqg_put(cfqd->root_group);
    > >
    > > This seems to be a spurious cfqg_put()? Which reference we are putting
    > > down here?
    >
    > The extra ref from cfq_link_cfqq_cfqg() for oom_cfqq; otherwise, we
    > need an extra cfq_put() in cfq_exit_queue(). I thought I wrote
    > comment about that somewhere. Hmmm.... apparently not. The thing is
    > that oom_cfqq doesn't go through proper cfqq destruction and thus
    > never puts the extra ref to root cfqg.

    Ok. Is cfq_exit_queue() a better place to put down this reference
    explicitly with a comment. Even if you keep it here, atleast a comment
    is required. It is not obvious at all (atleast to me).

    Thanks
    Vivek


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