From mboxrd@z Thu Jan  1 00:00:00 1970
From: Xiao Guangrong <xiaoguangrong.eric@gmail.com>
Subject: Re: [PATCH v4] kvm: make vcpu life cycle separated from kvm instance
Date: Thu, 15 Dec 2011 16:57:56 +0800
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Cc: Liu ping fan <kernelfans@gmail.com>, kvm@vger.kernel.org,
	linux-kernel@vger.kernel.org, avi@redhat.com, aliguori@us.ibm.com,
	gleb@redhat.com, mtosatti@redhat.com, jan.kiszka@web.de
To: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
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On 12/15/2011 04:25 PM, Xiao Guangrong wrote:

> On 12/15/2011 02:53 PM, Liu ping fan wrote:
> 
> 
>>
>>>> +struct kvm_vcpu *kvm_vcpu_get(struct kvm_vcpu *vcpu)
>>>> +{
>>>> +     if (vcpu == NULL)
>>>> +             return NULL;
>>>> +     if (atomic_add_unless(&vcpu->refcount, 1, 0))
>>>
>>>
>>> Why do not use atomic_inc()?
>>> Also, i think a memory barrier is needed after increasing refcount.
>>>
>> Because when refcout==0, we prepare to destroy vcpu, and do not to
>> disturb it by increasing the refcount.
> 
> 
> Oh, get it.
> 


But i think we can do it like this:

On the vcpu free path:

hold kvm->lock
delete vcpu from the kvm->vcpus
release kvm->lock

synchronize_rcu()
kvm_vcpu_put()

then, we can avoid get invalid instance and it can make the code simple?