linux-kernel - Re: [PATCH 2/2] block: Avoid deadlocks with bio allocation by stacking drivers

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Message-ID: <20120910231326.GG7677@google.com>
Date:	Mon, 10 Sep 2012 16:13:26 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Kent Overstreet <koverstreet@...gle.com>
Cc:	linux-bcache@...r.kernel.org, linux-kernel@...r.kernel.org,
	dm-devel@...hat.com, axboe@...nel.dk,
	Vivek Goyal <vgoyal@...hat.com>,
	Mikulas Patocka <mpatocka@...hat.com>, bharrosh@...asas.com,
	david@...morbit.com
Subject: Re: [PATCH 2/2] block: Avoid deadlocks with bio allocation by
 stacking drivers

Hello, again.

On Mon, Sep 10, 2012 at 03:09:10PM -0700, Tejun Heo wrote:
> I'm still a bit scared but think this is correct.
> 
>  Acked-by: Tejun Heo <tj@...nel.org>
> 
> One last thing is that we may want to add @name on bioset creation so
> that we can name the workqueue properly but that's for another patch.

Yet another thing that I noticed in a different discussion.

  http://thread.gmane.org/gmane.linux.network.drbd.devel/2130

Before this, I think bios didn't get reordered while they're traveling
down the stacked bio drivers.  After this, I don't think that's true
anymore.  Currently, IIRC, we don't have any ordering functionality at
bio interface, so I don't think this breaks anything but this can lead
to stupidly subtle bugs if the upper layer is making assumption on
ordering somehow.  It's something which at least should be noted, I
think.  Whether we want to update the code so that ordering is
maintained, I don't know.  I hope not.  It's already crazy complex. :(

Thanks.

-- 
tejun
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