linux-kernel - Re: [REGRESSION] [PATCH] block: uninitialized ioc->nr_tasks triggers WARN

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Message-ID: <20120717222444.GG24336@google.com>
Date:	Tue, 17 Jul 2012 15:24:44 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Olof Johansson <olof@...om.net>
Cc:	axboe@...nel.dk, linux-kernel@...r.kernel.org, vgoyal@...hat.com,
	torvalds@...ux-foundation.org
Subject: Re: [REGRESSION] [PATCH] block: uninitialized ioc->nr_tasks
 triggers WARN_ON

Hello, Olof.

On Tue, Jul 17, 2012 at 02:36:43PM -0700, Olof Johansson wrote:
> It seems like the init of ioc->nr_tasks was removed in that patch,
> so it starts out at 0 instead of 1.
> 
> Tejun, is the right thing here to add back the init, or should something else
> be done?
>
> The below patch removes the warning, but I haven't done any more extensive
> testing on it.
> 
> 
> Signed-off-by: Olof Johansson <olof@...om.net>

Right, the patch shouldn't have replaced the init.

 Acked-by: Tejun Heo <tj@...nel.org>

Fortunately, the effect of the bug is limited.  ioc->nr_tasks only
used to veto block cgroup migration if a task has ioc which is shared
by multiple tasks.  Currently, the only known program using CLONE_IO
is dump and even if somebody migrates some threads of a single dump
instance to a different block cgroup, the result won't be catastrophic
although block cgroup policies would become ambiguous.  IMHO, it
should be okay to route this through -stable after 3.5.  Jens?

Thanks.

-- 
tejun
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