On Mon, Aug 08, 2016 at 12:20:14PM +0100, Andre Przywara wrote:
> Hi,
>
> On 03/08/16 17:13, Christoffer Dall wrote:
> > Right now the following sequence of events can happen:
> >
> > 1. Thread X calls vgic_put_irq
> > 2. Thread Y calls vgic_add_lpi
> > 3. Thread Y gets lpi_list_lock
> > 4. Thread X drops the ref count to 0 and blocks on lpi_list_lock
> > 5. Thread Y finds the irq via the lpi_list_lock, raises the ref
> > count to 1, and release the lpi_list_lock.
> > 6. Thread X proceeds and frees the irq.
> >
> > Avoid this by holding the spinlock around the kref_put.
> >
> > Signed-off-by: Christoffer Dall <christoffer.dall@xxxxxxxxxx>
> > ---
> > virt/kvm/arm/vgic/vgic.c | 20 ++++++++++----------
> > 1 file changed, 10 insertions(+), 10 deletions(-)
> >
> > diff --git a/virt/kvm/arm/vgic/vgic.c b/virt/kvm/arm/vgic/vgic.c
> > index e7aeac7..fb8c0ab 100644
> > --- a/virt/kvm/arm/vgic/vgic.c
> > +++ b/virt/kvm/arm/vgic/vgic.c
> > @@ -117,22 +117,22 @@ static void vgic_irq_release(struct kref *ref)
> >
> > void vgic_put_irq(struct kvm *kvm, struct vgic_irq *irq)
> > {
> > - struct vgic_dist *dist;
> > + struct vgic_dist *dist = &kvm->arch.vgic;
> >
> > if (irq->intid < VGIC_MIN_LPI)
> > return;
> >
> > - if (!kref_put(&irq->refcount, vgic_irq_release))
> > - return;
> > -
> > - dist = &kvm->arch.vgic;
> > -
> > spin_lock(&dist->lpi_list_lock);
> > - list_del(&irq->lpi_list);
> > - dist->lpi_list_count--;
> > - spin_unlock(&dist->lpi_list_lock);
> > + if (!kref_put(&irq->refcount, vgic_irq_release)) {
> > + spin_unlock(&dist->lpi_list_lock);
> > + return;
> > + } else {
>
> Just a nit, I guess, but we don't need this "else" since the if-branch
> always returns?
>
correct, I can change that.
> > + list_del(&irq->lpi_list);
> > + dist->lpi_list_count--;
> > + spin_unlock(&dist->lpi_list_lock);
> >
> > - kfree(irq);
> > + kfree(irq);
> > + }
> > }
> >
> > /**
> >
>
> Otherwise:
>
> Reviewed-by: Andre Przywara <andre.przywara@xxxxxxx>
>
Thanks.
-Christoffer
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