linux-kernel - Re: [PATCH] block: fix block

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Message-ID: <20080721193426.28ad925c@gondolin>
Date:	Mon, 21 Jul 2008 19:34:26 +0200
From:	Cornelia Huck <cornelia.huck@...ibm.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jens Axboe <jens.axboe@...cle.com>, Greg K-H <greg@...ah.com>
Subject: Re: [PATCH] block: fix block_class iteration locking

On Mon, 14 Jul 2008 20:50:57 +0900,
Tejun Heo <tj@...nel.org> wrote:

> > With your patch, you protect against adding/removing devices to/from
> > the class between _start and _stop. This wasn't done previously, and
> > won't be done with Greg's patches (which leaves in the
> > locking/unlocking of block_class_lock). Not sure if I'm missing
> > something here...
> 
> That's mostly the point of this patch.  It wasn't protected properly
> before.  It would be best if there's a safe iterator (maybe use klist?).

Hm, I don't see how a klist would help here since it still allows to
add/remove devices during walking the file.

What we need is more like a "lock/unlock the device list" operation and
a lockless iterator - that would give the same semantics as your patch.
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