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 10/13] block, cfq: unlink cfq_io_context's immediately
Date: Wed, 26 Oct 2011 13:54:55 -0700 [thread overview]
Message-ID: <20111026205455.GG24261@google.com> (raw)
In-Reply-To: <20111026203846.GG355@redhat.com>
Hello, Vivek.
On Wed, Oct 26, 2011 at 04:38:46PM -0400, Vivek Goyal wrote:
> So the only reason that cic needs to be rcu protected because in
> cfq_cic_lookup() we can access ioc->ioc_data which can point to a
> cic which is not ours and we are not holding queue lock for that and
> we can't access cic->q ?
About right but to be more exact.
* Indexes from ioc are protected by ioc->lock - both the radix tree
and hint. Both are RCU managed.
* cic structures themselves are protected by cic->q->queue_lock and
RCU managed.
* Additions and removals are done holding both ioc and q locks.
* Lookup is performed with RCU read locked and q->queue_lock held.
Indexes and cic's themselves are RCU protected so can be traversed
and cic can be dereferenced even if it's pointing to a different
queue (and thus protected under different queue_lock).
However, cic's pointing to the q which is being looked up can be
added only under the same queue_lock, so on "cic->q == q" we're
guaranteed to be looking at the right thing.
> I am wondering if there should be a small text file explaining all
> the locking in this area.
Oh, I'm gonna be restructuring ioc interface and adding ample
explanations on locking rules there.
Thanks.
--
tejun
next prev parent reply other threads:[~2011-10-26 20:55 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-10-26 1:48 [PATCHSET block:for-3.2/core] rescue cfq from RCU death sprial :) Tejun Heo
2011-10-26 1:48 ` [PATCH 01/13] ida: make ida_simple_get/put() IRQ safe Tejun Heo
2011-10-26 4:42 ` Rusty Russell
2011-10-26 20:28 ` Tejun Heo
2011-10-26 1:48 ` [PATCH 02/13] block, cfq: move cfqd->cic_index to q->id Tejun Heo
2011-10-26 1:48 ` [PATCH 03/13] block: misc ioc cleanups Tejun Heo
2011-10-26 1:48 ` [PATCH 04/13] block: make ioc get/put interface more conventional and fix race on alloction Tejun Heo
2011-10-26 16:01 ` Vivek Goyal
2011-10-26 19:29 ` Tejun Heo
2011-10-26 21:30 ` [PATCH UPDATED " Tejun Heo
2011-10-26 1:48 ` [PATCH 05/13] block: misc updates to blk_get_queue() Tejun Heo
2011-10-26 1:48 ` [PATCH 06/13] block, cfq: misc updates to cfq_io_context Tejun Heo
2011-10-27 15:39 ` Vivek Goyal
2011-10-27 16:24 ` Tejun Heo
2011-10-26 1:48 ` [PATCH 07/13] block, cfq: move ioc ioprio/cgroup changed handling to cic Tejun Heo
2011-10-26 1:48 ` [PATCH 08/13] block, cfq: fix race condition in cic creation path and tighten locking Tejun Heo
2011-10-26 1:48 ` [PATCH 09/13] block, cfq: fix cic lookup locking Tejun Heo
2011-10-26 1:48 ` [PATCH 10/13] block, cfq: unlink cfq_io_context's immediately Tejun Heo
2011-10-26 19:48 ` Vivek Goyal
2011-10-26 19:55 ` Tejun Heo
2011-10-26 20:38 ` Vivek Goyal
2011-10-26 20:54 ` Tejun Heo [this message]
2011-10-26 21:31 ` [PATCH UPDATED " Tejun Heo
2011-10-27 14:31 ` Vivek Goyal
2011-10-27 16:17 ` Tejun Heo
2011-10-27 17:05 ` Vivek Goyal
2011-10-27 17:11 ` Tejun Heo
2011-10-26 1:48 ` [PATCH 11/13] block, cfq: remove delayed unlink Tejun Heo
2011-10-26 1:48 ` [PATCH 12/13] block, cfq: kill ioc_gone Tejun Heo
2011-10-26 1:48 ` [PATCH 13/13] block, cfq: kill cic->key Tejun Heo
2011-10-26 21:36 ` [PATCHSET block:for-3.2/core] rescue cfq from RCU death sprial :) Tejun Heo
2011-10-27 15:32 ` Vivek Goyal
2011-10-27 16:10 ` Tejun Heo
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