Re: [PATCH 3/3] KVM: make make_all_cpus_request() lockless

From: Xiao Guangrong
Date: Wed Jan 05 2011 - 05:08:33 EST


On 01/05/2011 05:54 PM, Avi Kivity wrote:

>> + kvm_make_request(req, vcpu);
>> cpu = vcpu->cpu;
>> if (cpus != NULL&& cpu != -1&& cpu != me&&
>> atomic_read(&vcpu->guest_mode))
>> @@ -163,7 +161,7 @@ static bool make_all_cpus_request(struct kvm *kvm, unsigned int req)
>> smp_call_function_many(cpus, ack_flush, NULL, 1);
>> else
>> called = false;
>> - raw_spin_unlock(&kvm->requests_lock);
>> + put_cpu();
>> free_cpumask_var(cpus);
>> return called;
>> }
>
> Maybe we can drop 'cpu != me' and then we don't need to disable preemption?
>

Preemption should be disabled in the caller site of smp_call_function_many():

......

* You must not call this function with disabled interrupts or from a
* hardware interrupt handler or from a bottom half handler. Preemption
* must be disabled when calling this function.
*/
void smp_call_function_many(const struct cpumask *mask,
smp_call_func_t func, void *info, bool wait)
{

......

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