Re: [Qemu-devel] [RFC] vhost: Can we change synchronize_rcu to call_rcu in vhost_set_memory() in vhost kernel module?

[Paolo Bonzini]

Il 12/05/2014 12:08, Michael S. Tsirkin ha scritto:
> On Mon, May 12, 2014 at 11:57:32AM +0200, Paolo Bonzini wrote:
> > Perhaps we can check for cases where only the address is changing,
> > and poke at an existing struct kvm_kernel_irq_routing_entry without
> > doing any RCU synchronization?
>
> I suspect interrupts can get lost then: e.g. if address didn't match any
> cpus, now it matches some. No?

Can you explain the problem more verbosely? :)

Multiple writers would still be protected by the mutex, so you cannot 
have an "in-place update" writer racing with a "copy the array" writer.

Paolo