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
Subject: Re: [PATCH 2/9] blkcg: drop unnecessary RCU locking
Date: Fri, 17 Feb 2012 09:11:13 -0800 [thread overview]
Message-ID: <20120217171113.GB26575@google.com> (raw)
In-Reply-To: <20120217164749.GC26620@redhat.com>
On Fri, Feb 17, 2012 at 11:47:49AM -0500, Vivek Goyal wrote:
> So now in some cases we call blkg_lookup_create() with both queue and rcu
> read lock held (cfq_lookup_create_cfqg()) and in this case hold only queue
> lock.
So, this should be okay. It's currently not because blkg_alloc() is
broken due to percpu allocation but other than that calling both w/
and w/o RCU read lock should be fine.
> blkg_lookup_create() calls blkg_lookup() which expects a rcu_read_lock()
> to be held and we will be travesing that list without rcu_read_lock()
> held. Isn't that a problem?
No, why would it be a problem?
> We might be examining a blkg belonging to a different queue and it
> might be being freed parallely.
How?
Thanks.
--
tejun
next prev parent reply other threads:[~2012-02-17 17:11 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-16 22:37 [PATCHSET] blkcg: update locking and fix stacking Tejun Heo
2012-02-16 22:37 ` [PATCH 1/9] blkcg: use double locking instead of RCU for blkg synchronization Tejun Heo
2012-02-16 22:37 ` [PATCH 2/9] blkcg: drop unnecessary RCU locking Tejun Heo
2012-02-17 16:19 ` Vivek Goyal
2012-02-17 17:07 ` Tejun Heo
2012-02-17 17:14 ` Tejun Heo
2012-02-17 16:47 ` Vivek Goyal
2012-02-17 17:11 ` Tejun Heo [this message]
2012-02-17 17:28 ` Vivek Goyal
2012-02-17 17:43 ` Tejun Heo
2012-02-17 18:08 ` Vivek Goyal
2012-02-17 18:16 ` Tejun Heo
2012-02-22 0:49 ` [PATCH UPDATED " Tejun Heo
2012-02-16 22:37 ` [PATCH 3/9] block: restructure get_request() Tejun Heo
2012-02-16 22:37 ` [PATCH 4/9] block: interface update for ioc/icq creation functions Tejun Heo
2012-02-16 22:37 ` [PATCH 5/9] block: ioc_task_link() can't fail Tejun Heo
2012-02-17 20:41 ` Vivek Goyal
2012-02-17 22:18 ` Tejun Heo
2012-02-16 22:37 ` [PATCH 6/9] block: add io_context->active_ref Tejun Heo
2012-02-16 22:37 ` [PATCH 7/9] block: implement bio_associate_current() Tejun Heo
2012-02-17 1:19 ` Kent Overstreet
2012-02-17 22:14 ` Tejun Heo
2012-02-17 22:34 ` Vivek Goyal
2012-02-17 22:41 ` Tejun Heo
2012-02-17 22:51 ` Vivek Goyal
2012-02-17 22:57 ` Tejun Heo
2012-02-20 14:22 ` Vivek Goyal
2012-02-20 16:59 ` Tejun Heo
2012-02-20 19:14 ` Vivek Goyal
2012-02-20 21:21 ` Tejun Heo
2012-02-27 23:12 ` Chris Wright
2012-02-28 14:10 ` Vivek Goyal
2012-02-28 17:01 ` Chris Wright
2012-02-28 20:11 ` Stefan Hajnoczi
2012-02-20 14:36 ` Vivek Goyal
2012-02-20 17:01 ` Tejun Heo
2012-02-20 19:16 ` Vivek Goyal
2012-02-20 21:06 ` Tejun Heo
2012-02-20 21:10 ` Vivek Goyal
2012-02-17 22:56 ` Vivek Goyal
2012-02-17 23:06 ` Tejun Heo
2012-02-17 21:33 ` Vivek Goyal
2012-02-17 22:03 ` Tejun Heo
2012-02-17 22:29 ` Vivek Goyal
2012-02-17 22:38 ` Tejun Heo
2012-02-17 22:42 ` Tejun Heo
2012-02-16 22:37 ` [PATCH 8/9] block: make block cgroup policies follow bio task association Tejun Heo
2012-02-16 22:37 ` [PATCH 9/9] block: make blk-throttle preserve the issuing task on delayed bios Tejun Heo
2012-02-17 21:58 ` Vivek Goyal
2012-02-17 22:17 ` Tejun Heo
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