linux-kernel - Re: [KVM PATCH v3 3/3] KVM: Fix races in irqfd using new eventfd_kref

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Message-ID: <alpine.DEB.1.10.0906221140570.10952@makko.or.mcafeemobile.com>
Date:	Mon, 22 Jun 2009 11:41:53 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	"Michael S. Tsirkin" <mst@...hat.com>
cc:	Gregory Haskins <gregory.haskins@...il.com>,
	Gregory Haskins <ghaskins@...ell.com>, kvm@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	avi@...hat.com, paulmck@...ux.vnet.ibm.com,
	Ingo Molnar <mingo@...e.hu>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [KVM PATCH v3 3/3] KVM: Fix races in irqfd using new eventfd_kref_get
 interface

On Mon, 22 Jun 2009, Michael S. Tsirkin wrote:

> On Mon, Jun 22, 2009 at 11:11:12AM -0700, Davide Libenzi wrote:
> > On Mon, 22 Jun 2009, Michael S. Tsirkin wrote:
> > 
> > > Not really, it's impossible to document all races one have thought
> > > about and avoided.
> > 
> > Well, when some new code has non-trivial locking/racing logics, you better 
> > document it as clearly as possible, akpm announced time ago.
> 
> Absolutely. But IMO documentation in the form of "fields A B C are
> protected by lock X" in a single place near field declaration is better
> than "we take lock X here to protect against race with user thread using
> fields A B C" sprinkled all over the code.

Exactly what akpm suggested. A fat comment on top of the C file describing 
locking logic and pitfalls.


- Davide


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