Messages in this thread | | | Date | Tue, 24 Jan 2012 11:32:24 -0500 | From | Vivek Goyal <> | Subject | Re: [PATCH 14/16] blkcg: don't allow or retain configuration of missing devices |
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On Tue, Jan 24, 2012 at 07:53:09AM -0800, Tejun Heo wrote: > On Tue, Jan 24, 2012 at 10:42:24AM -0500, Vivek Goyal wrote: > > On Mon, Jan 23, 2012 at 03:09:51PM -0800, Tejun Heo wrote: > > > + disk = get_gendisk(dev, &part); > > > + > > > + if ((!disk || part) && temp) { > > > + ret = -ENODEV; > > > + goto out; > > > + } > > > + > > > + rcu_read_lock(); > > > + > > > + if (disk && !part) { > > > + spin_lock_irq(disk->queue->queue_lock); > > > + blkg = blkg_lookup_create(blkcg, disk->queue, plid); > > > + spin_unlock_irq(disk->queue->queue_lock); > > > > If queue is in bypass mode, is group creation and linking allowed when > > somebody is trying to set per device rules. (/me is thinking if there are > > any potential races between elevator switch and rule setting in cgroup). > > Yeap, there is. Nice catch. blkg_lookup_create() should be testing > blk_queue_bypass() instead of blk_queue_dead() and parse_and_set > should probably retry after a bit. Will update.
So now group creation fails if queue is in bypass mode. So a per device rule setting will fail both for cfq and throttling logic while device is still around. So a user is supposed to retry? How would a user know that elevator switch is happening and he should retry and till when should he retry.
Thanks Vivek
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