linux-kernel - Re: [PATCH v3.4-rc5] block: iocontext->nr

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Message-ID: <20120501180906.GX26595@google.com>
Date:	Tue, 1 May 2012 11:09:06 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Jens Axboe <jaxboe@...ionio.com>
Cc:	Dave Jones <davej@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Sasha Levin <levinsasha928@...il.com>
Subject: Re: [PATCH v3.4-rc5] block: iocontext->nr_tasks should be
 initialized to one

On Tue, May 01, 2012 at 08:02:39PM +0200, Jens Axboe wrote:
> On 2012-05-01 18:17, Tejun Heo wrote:
> > create_task_io_context() left ioc->nr_tasks at zero; however, a newly
> > created ioc should have its nr_tasks initialized to one as it begins
> > attached to the task creating it.
> > 
> > This affects only CLONE_IO which currently doesn't seem to have any
> > actual user.  Sasha triggered WARN_ON_ONCE() in ioc_task_link() using
> > syscall fuzzer.  Even when it happens, the failure mode isn't critical
> > (blk-cgroup may allow attaching a CLONE_IO'd task to a cgroup when it
> > shouldn't and blkcg limits may behave weirdly).
> 
> CLONE_IO is an exported interface, it can be set from clone(2).
> Otherwise Sasha would not have hit this :-)

Yeah, but with pthread not exposing it, I'm very skeptical how much,
if any, use it's getting.  With its incompatibility with blk-cgroup
and cfq being able to merge coop request streams, I'm not sure how
much we need it.  Maybe we can just make it noop?

Thanks.

-- 
tejun
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