Re: [PATCH] KVM_SET_MEMORY_REGION hang in linux 2.6.23.y

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Marko Kohtala wrote:
> Wait for right amount of tlb flushes. Completed can be larger than
> needed and therefore the loop waiting them to match never ends.
>
> Signed-off-by: Marko Kohtala <marko.kohtala-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
>
> ---
>
> This solves kernel lockup in KVM_SET_MEMORY_REGION ioctl with Linux
> 2.6.23.8 and before at kvm-52 start. Not needed in 2.6.24.
>
> diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
> index cd05579..b148aff 100644
> --- a/drivers/kvm/kvm_main.c
> +++ b/drivers/kvm/kvm_main.c
> @@ -279,7 +279,8 @@ void kvm_flush_remote_tlbs(struct kvm *kvm)
>  	 * to complete.
>  	 */
>  	for (cpu = first_cpu(cpus); cpu != NR_CPUS; cpu = next_cpu(cpu, cpus))
> -		smp_call_function_single(cpu, ack_flush, &completed, 1, 0);
> +		if (cpu_isset(cpu, cpus))
> +			smp_call_function_single(cpu, ack_flush, &completed, 1, 0);
>   

Can you explain how this makes a difference?  Aren't first_cpu() and 
next_cpu() designed to iterate over all cpus which have cpu_isset(cpus)?

-- 
Any sufficiently difficult bug is indistinguishable from a feature.


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