From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jeremy Fitzhardinge <jeremy@goop.org>
Subject: Re: [PATCH] Fix memory order issue inside pv spinlock
Date: Tue, 08 Sep 2009 14:59:43 -0700
Message-ID: <4AA6D3CF.70905@goop.org>
References: <4AA4B8FF.9070905@intel.com>
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To: "Yang, Xiaowei" <xiaowei.yang@intel.com>
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On 09/07/09 00:40, Yang, Xiaowei wrote:
> barrier() can't prevent reads after it not being reordered with older
> writes to different locates before it. Because of it, I can't bring up
> > 4 HVM guests on one SMP machine. Use mb() instead.

Which read is happening too early?  Is it "xl->spinners"?  How does it fail?

Thanks,
    J

>
> Signed-off-by: Yang Xiaowei <xiaowei.yang@intel.com>
>
> diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
> index 5601506..9dee5f8 100644
> --- a/arch/x86/xen/spinlock.c
> +++ b/arch/x86/xen/spinlock.c
> @@ -324,7 +325,7 @@ static void xen_spin_unlock(struct raw_spinlock
> *lock)
>         xl->lock = 0;           /* release lock */
>
>         /* make sure unlock happens before kick */
> -       barrier();
> +       mb();
>
>         if (unlikely(xl->spinners))
>                 xen_spin_unlock_slow(xl);
>
> Thanks,
> Xiaowei
>