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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 10:16:34 -0800	[thread overview]
Message-ID: <20120217181634.GD29414@google.com> (raw)
In-Reply-To: <20120217180800.GE26620@redhat.com>

On Fri, Feb 17, 2012 at 01:08:00PM -0500, Vivek Goyal wrote:
> > Modifying blkgs require both blkcg and queue locks,
> > so read access can be done holding any lock.
> 
> This is the point I am not getting. How blkg_lookup() is safe just
> under queue lock. What stops freeing up blkg associated with other
> queues. I thought caller needs to hold rcu_read_lock() also to
> make sure it can safely compare blkg->q == q and return the blkg
> belonging to the queue in question.

Ooh, you're right.  I got confused.  We should be holding either blkcg
lock or rcu_read_lock() across blkg_lookup().  Will update.

Thanks.

-- 
tejun

  reply	other threads:[~2012-02-17 18:16 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
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 [this message]
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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