linux-kernel - Re: [PATCH 3/3] eventfd: add internal reference counting to fix notifier race conditions

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Message-Id: <200906231255.17015.rusty@rustcorp.com.au>
Date:	Tue, 23 Jun 2009 12:55:16 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Davide Libenzi <davidel@...ilserver.org>
Cc:	Gregory Haskins <ghaskins@...ell.com>, mst@...hat.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>
Subject: Re: [PATCH 3/3] eventfd: add internal reference counting to fix notifier race conditions

On Mon, 22 Jun 2009 09:24:20 am Davide Libenzi wrote:
> I actually ended up exposing the eventfd context anyway, since IMO is a
> better option instead of holding references to the eventfd file (that
> makes VFS people uneasy).

lguest is a special case since we don't let them close the fds, except by 
closing /dev/lguest.

Lguest change seems fine, but:

> Index: linux-2.6.mod/drivers/lguest/lg.h
> ===================================================================
> --- linux-2.6.mod.orig/drivers/lguest/lg.h	2009-06-21 15:55:17.000000000
> -0700 +++ linux-2.6.mod/drivers/lguest/lg.h	2009-06-21 15:56:00.000000000
> -0700 @@ -80,9 +80,11 @@ struct lg_cpu {
>  	struct lg_cpu_arch arch;
>  };
>
> +struct eventfd_ctx;
> +
>  struct lg_eventfd {
>  	unsigned long addr;
> -	struct file *event;
> +	struct eventfd_ctx *event;
>  };

The first 'struct eventfd_ctx;' line is not required.

Thanks,
Rusty.
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