Messages in this thread | | | Date | Thu, 15 Mar 2012 10:18:08 -0700 | From | Tejun Heo <> | Subject | Re: [PATCH block/for-3.4/core] cfq: fix cfqg ref handling when BLK_CGROUP && !CFQ_GROUP_IOSCHED |
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On Thu, Mar 15, 2012 at 01:01:00PM -0400, Vivek Goyal wrote: > 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).
Ah... the comment actually already is there.
/* * Our fallback cfqq if cfq_find_alloc_queue() runs into OOM issues. * Grab a permanent reference to it, so that the normal code flow * will not attempt to free it. oom_cfqq is linked to root_group * but shouldn't hold a reference as it'll never be unlinked. Lose * the reference from linking right away. */
-- tejun
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