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

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Message-ID: <4FA025CA.9060506@fusionio.com>
Date:	Tue, 1 May 2012 20:04:58 +0200
From:	Jens Axboe <jaxboe@...ionio.com>
To:	Tejun Heo <tj@...nel.org>
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 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).
> 
> Fix it by initializing it to one in create_task_io_context().
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Reported-by: Sasha Levin <levinsasha928@...il.com>
> LKML-Reference: <1335873936.16988.148.camel@...py>
> Cc: stable@...r.kernel.org

BTW, this only affects for-3.5/core, it's not a mainline bug. So I've
dropped the stable CC.

-- 
Jens Axboe

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