linux-kernel - Re: [PATCH 3/4] xen/manage: Guard against user-space initiated poweroff and XenBus.

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Message-ID: <528DEA00.7070505@citrix.com>
Date:	Thu, 21 Nov 2013 11:09:52 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	<Ian.Campbell@...rix.com>, <xen-devel@...ts.xenproject.org>,
	<linux-kernel@...r.kernel.org>, <JBeulich@...e.com>,
	<boris.ostrovsky@...cle.com>
Subject: Re: [PATCH 3/4] xen/manage: Guard against user-space initiated poweroff
 and XenBus.

On 08/11/13 17:38, Konrad Rzeszutek Wilk wrote:
> There is a race case where the user does 'poweroff'
> and at the same time the system admin does 'xl shutdown'.

This isn't a Xen-specific problem is it?  Wouldn't it be better to fix
this in generic code?

Especially since I don't think this patch actually fixes the race
completely.

> --- a/drivers/xen/manage.c
> +++ b/drivers/xen/manage.c
[...]
> @@ -222,7 +230,7 @@ static void shutdown_handler(struct xenbus_watch *watch,
>  	};
>  	static struct shutdown_handler *handler;
>  
> -	if (shutting_down != SHUTDOWN_INVALID)
> +	if (atomic_read(&shutting_down) != SHUTDOWN_INVALID)
>  		return;

In guest initiated poweroff at this time will still race with this
toolstack initiated poweroff.

David
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