From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Jan Beulich" <JBeulich@novell.com>
Subject: RE: Re: [PATCH] Fix cpu offline bug
Date: Tue, 08 Mar 2011 10:14:08 +0000
Message-ID: <4D760F8002000078000351E8@vpn.id2.novell.com>
References: <BC00F5384FCFC9499AF06F92E8B78A9E1FA4F5A806@shsmsx502.ccr.corp.intel.com>
	<C9967421.14234%keir.xen@gmail.com>
	<4D75FC5702000078000351B2@vpn.id2.novell.com>
	<BC00F5384FCFC9499AF06F92E8B78A9E1FABB28525@shsmsx502.ccr.corp.intel.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: quoted-printable
Return-path: <xen-devel-bounces@lists.xensource.com>
In-Reply-To: <BC00F5384FCFC9499AF06F92E8B78A9E1FABB28525@shsmsx502.ccr.corp.intel.com>
Content-Disposition: inline
List-Unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
List-Post: <mailto:xen-devel@lists.xensource.com>
List-Help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-Subscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
Sender: xen-devel-bounces@lists.xensource.com
Errors-To: xen-devel-bounces@lists.xensource.com
To: Jinsong Liu <jinsong.liu@intel.com>
Cc: "xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>, Keir Fraser <keir.xen@gmail.com>, Xin Li <xin.li@intel.com>, Yunhong Jiang <yunhong.jiang@intel.com>
List-Id: xen-devel@lists.xenproject.org

>>> On 08.03.11 at 10:47, "Liu, Jinsong" <jinsong.liu@intel.com> wrote:
> Jan, I'm not quite clear your meaning.
> Why and where need to insert barrier, or volatile cpu_state?
=20
     while ( (seen_state =3D cpu_state) !=3D CPU_STATE_DEAD )
     {
+        barrier();
         BUG_ON(seen_state !=3D CPU_STATE_DYING);
         mdelay(100);
         cpu_relax();

Without this, the compiler is free to eliminate "seen_state" in favor
of reading "cpu_state" twice (irrespective of the optimizer very
likely trying to do exactly the opposite).

Jan