>>>>>> +
>>>>>> +static inline void
>>>>>> +_kvm_xinterface_release(struct kref *kref)
>>>>>> +{
>>>>>> + struct kvm_xinterface *intf;
>>>>>> + struct module *owner;
>>>>>> +
>>>>>> + intf = container_of(kref, struct kvm_xinterface, kref);
>>>>>> +
>>>>>> + owner = intf->owner;
>>>>>> + rmb();
>>>>>>
>>>>>>
>>>>>>
>>>>> Why rmb?
>>>>>
>>>>>
>>>> the intf->ops->release() line may invalidate the intf pointer, so we
>>>> want to ensure that the read completes before the release() is called.
>>>>
>>>> TBH: I'm not 100% its needed, but I was being conservative.
>>>>
>>>>
>>> rmb()s are only needed if an external agent can issue writes, otherwise
>>> you'd need one after every statement.
>>>
>> I was following lessons learned here:
>>
>>
http://lkml.org/lkml/2009/7/7/175
>>
>> Perhaps mb() or barrier() are more appropriate than rmb()? I'm CC'ing
>> David Howells in case he has more insight.
>>
> BTW: In case it is not clear, the rationale as I understand it is we
> worry about the case where one cpu reorders the read to be after the
> ->release(), and another cpu might grab the memory that was kfree()'d
> within the ->release() and scribble something else on it before the read
> completes.
>
> I know rmb() typically needs to be paired with wmb() to be correct, so
> you are probably right to say that the rmb() itself is not appropriate.
> This problem in general makes my head hurt, which is why I said I am
> not 100% sure of what is required. As David mentions, perhaps
> "smp_mb()" is more appropriate for this application. I also speculate
> barrier() may be all that we need.
>
