linux-kernel - Re: [PATCH v7 9/9] block: Avoid deadlocks with bio allocation by stacking drivers

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Message-ID: <20120828230108.GI1048@moria.home.lan>
Date:	Tue, 28 Aug 2012 16:01:08 -0700
From:	Kent Overstreet <koverstreet@...gle.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	linux-bcache@...r.kernel.org, linux-kernel@...r.kernel.org,
	dm-devel@...hat.com, vgoyal@...hat.com, mpatocka@...hat.com,
	bharrosh@...asas.com, Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH v7 9/9] block: Avoid deadlocks with bio allocation by
 stacking drivers

On Tue, Aug 28, 2012 at 03:28:00PM -0700, Kent Overstreet wrote:
> On Tue, Aug 28, 2012 at 01:49:10PM -0700, Tejun Heo wrote:
> > Overall, I *think* this is correct but need to think more about it to
> > be sure.
> 
> Please do. As much time as I've spent staring at this kind of stuff,
> I'm pretty sure I've got it correct but it still makes my head hurt to
> work out all the various possible deadlocks.

Hilarious thought: We're punting bios to a rescuer thread that's
specific to a certain bio_set, right? What if we happen to punt bios
from a different bio_set? And then the rescuer goes to resubmit those
bios, and in the process they happen to have dependencies on the
original bio_set...

I think it's actually necessary to filter out only bios from the current
bio_set to punt to the rescuer.

God I love the block layer sometimes.
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