linux-kernel - Re: [KVM PATCH v2 2/2] kvm: use POLLHUP to close an irqfd instead of an explicit ioctl

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Message-Id: <200906181446.31373.rusty@rustcorp.com.au>
Date:	Thu, 18 Jun 2009 14:46:30 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Gregory Haskins <ghaskins@...ell.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, avi@...hat.com,
	davidel@...ilserver.org, paulmck@...ux.vnet.ibm.com,
	akpm@...ux-foundation.org
Subject: Re: [KVM PATCH v2 2/2] kvm: use POLLHUP to close an irqfd instead of an explicit ioctl

On Mon, 15 Jun 2009 10:24:39 pm Michael S. Tsirkin wrote:
> On Mon, Jun 15, 2009 at 08:08:18AM -0400, Gregory Haskins wrote:
> > Hmm.  I understand what you are saying conceptually (i.e. the .text
> > could get yanked before we hit the next line of code, in this case the
> > "return 0").  However, holding a reference when you _know_ someone else
> > holds a reference to me says that one of the references is redundant.
> > In addition, there is certainly plenty of precedence for
> > module_put(THIS_MODULE) all throughout the kernel (including
> > module_put_and_exit()).  Are those broken as well?
>
> Maybe not, but I don't know why. It works fine as long as you don't
> unload any modules though :) Rusty, could you enlighten us please?

Yep, they're almost all broken.  A few have comments indicating that someone 
else is holding a reference (eg. loopback).

But at some point you give up playing whack-a-mole for random drivers.

module_put_and_exit() does *not* have this problem, BTW.

Rusty.
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