Re: [patch 2/4] KVM: move coalesced_mmio locking to its own device

Avi Kivity
2009-05-31T12:14:37Z

Marcelo Tosatti wrote:
> Move coalesced_mmio locking to its own device, instead of relying on
> kvm->lock.
>
> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
>
> Index: kvm-irqlock/virt/kvm/coalesced_mmio.c
> ===================================================================
> --- kvm-irqlock.orig/virt/kvm/coalesced_mmio.c
> +++ kvm-irqlock/virt/kvm/coalesced_mmio.c
> @@ -26,9 +26,7 @@ static int coalesced_mmio_in_range(struc
> if (!is_write)
> return 0;
>
> - /* kvm->lock is taken by the caller and must be not released before
> - * dev.read/write
> - */
> + spin_lock(&dev->lock);
>

This unbalanced locking is still very displeasing. At a minimum you
need a sparse annotation to indicate it.

But I think it really indicates a problem with the io_device API.

Potential solutions:
- fold in_range() into ->write and ->read. Make those functions
responsible for both determining whether they can handle the range and
performing the I/O.
- have a separate rwlock for the device list.

--
error compiling committee.c: too many arguments to function