From: Tejun Heo <tj@kernel.org>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: axboe@kernel.dk, ctalbott@google.com, rni@google.com,
linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
containers@lists.linux-foundation.org
Subject: Re: [PATCH 07/11] blkcg: make request_queue bypassing on allocation
Date: Fri, 13 Apr 2012 14:16:40 -0700 [thread overview]
Message-ID: <20120413211640.GH12233@google.com> (raw)
In-Reply-To: <20120413210548.GG12233@google.com>
On Fri, Apr 13, 2012 at 02:05:48PM -0700, Tejun Heo wrote:
> On Fri, Apr 13, 2012 at 04:55:01PM -0400, Vivek Goyal wrote:
> > But neither seems to be the case here. So to make sure that blkg_lookup()
> > under rcu will see the updated value of queue flag (bypass), are we
> > relying on the fact that caller should see the DEAD flag and not go
> > ahead with blkg_lookup()? If yes, atleast it is not obivious.
>
> We're relying on the fact that it doesn't matter anymore because all
> blkgs will be shoot down in queue cleanup path which goes through rcu
> free, which is different from deactivating individual policies. It
> indeed is subtle. Umm... this is starting to get ridiculous. Why the
> hell was megaraid messing with so many queues anyways?
I suppose megaraid depends on sequential LUN scan which SCSI
implements by creating sdev for each LUN, trying to see whether it
actually exists and then destroys the sdev if not. Urgh.... so, we
seem to be stuck with it.
So, the current code is technically correct although subtle like hell.
We can RCU defer blk_put_queue() from blk_cleanup_queue() using
call_rcu() to make clear that RCU grace period is necessary there.
Any better ideas?
Thanks.
--
tejun
next prev parent reply other threads:[~2012-04-13 21:16 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-04-13 20:11 [PATCHSET] block: per-queue policy activation, take#2 Tejun Heo
2012-04-13 20:11 ` [PATCH 01/11] cfq: fix build breakage & warnings Tejun Heo
2012-04-13 20:11 ` [PATCH 02/11] blkcg: kill blkio_list and replace blkio_list_lock with a mutex Tejun Heo
2012-04-13 20:11 ` [PATCH 03/11] blkcg: use @pol instead of @plid in update_root_blkg_pd() and blkcg_print_blkgs() Tejun Heo
2012-04-13 20:11 ` [PATCH 04/11] blkcg: remove static policy ID enums Tejun Heo
2012-04-13 20:11 ` [PATCH 05/11] blkcg: make blkg_conf_prep() take @pol and return with queue lock held Tejun Heo
2012-04-13 20:11 ` [PATCH 06/11] blkcg: make sure blkg_lookup() returns %NULL if @q is bypassing Tejun Heo
2012-04-13 21:50 ` [PATCH UPDATED " Tejun Heo
2012-04-13 20:11 ` [PATCH 07/11] blkcg: make request_queue bypassing on allocation Tejun Heo
2012-04-13 20:32 ` Vivek Goyal
2012-04-13 20:37 ` Tejun Heo
2012-04-13 20:44 ` Vivek Goyal
2012-04-13 20:47 ` Tejun Heo
2012-04-13 20:55 ` Vivek Goyal
2012-04-13 21:05 ` Tejun Heo
2012-04-13 21:16 ` Tejun Heo [this message]
2012-04-13 21:31 ` Tejun Heo
2012-04-17 12:04 ` James Bottomley
2012-04-18 21:42 ` Tejun Heo
2012-04-13 21:33 ` Vivek Goyal
2012-04-13 21:38 ` Tejun Heo
2012-04-16 12:39 ` Vivek Goyal
2012-04-13 20:37 ` Vivek Goyal
2012-04-13 20:11 ` [PATCH 08/11] blkcg: add request_queue->root_blkg Tejun Heo
2012-04-13 20:11 ` [PATCH 09/11] blkcg: implement per-queue policy activation Tejun Heo
2012-04-13 20:11 ` [PATCH 10/11] blkcg: drop stuff unused after per-queue policy activation update Tejun Heo
2012-04-13 20:11 ` [PATCH 11/11] blkcg: shoot down blkgs if all policies are deactivated Tejun Heo
2012-04-20 8:09 ` [PATCHSET] block: per-queue policy activation, take#2 Jens Axboe
2012-04-20 12:02 ` Jens Axboe
2012-04-20 17:17 ` Tejun Heo
2012-04-20 19:08 ` Jens Axboe
2012-04-25 18:19 ` Tejun Heo
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