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[Xen-devel] Re: [PATCH] Fix memory order issue inside pv spinlock
| To: | "Yang, Xiaowei" <xiaowei.yang@xxxxxxxxx> |
|---|---|
| Subject: | [Xen-devel] Re: [PATCH] Fix memory order issue inside pv spinlock |
| From: | Jeremy Fitzhardinge <jeremy@xxxxxxxx> |
| Date: | Tue, 08 Sep 2009 14:59:43 -0700 |
| Cc: | "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx> |
| Delivery-date: | Tue, 08 Sep 2009 15:00:12 -0700 |
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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@xxxxxxxxx>
>
> 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
>
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