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    SubjectRe: [PATCH block/for-3.4/core] cfq: fix cfqg ref handling when BLK_CGROUP && !CFQ_GROUP_IOSCHED
    Hello,

    On Thu, Mar 15, 2012 at 12:46:21PM -0400, Vivek Goyal wrote:
    > On Thu, Mar 15, 2012 at 09:35:46AM -0700, Tejun Heo wrote:
    >
    > [..]
    > > ---
    > > Yeap, forgot to test that config combination. Fengguang, can you
    > > please test this patch? Jens, once Fengguang confirms the fix, can
    > > you please apply this on top of for-3.4/core along with the pending
    > > stats updates?
    >
    > I was working on similar patch and you beat me to it. :-) One comment
    > below.

    :)

    > [..]
    > > @@ -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.

    Thanks.

    --
    tejun


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