Re: [PATCH] KVM: use unified srcu interface function

Sean Christopherson
2022-12-09T01:22:16Z

On Thu, Dec 08, 2022, Hao Peng wrote:
> From: Peng Hao <flyingpeng@tencent.com>
>
> kvm->irq_routing is protected by kvm->irq_srcu.
>
> Signed-off-by: Peng Hao <flyingpeng@tencent.com>
> ---
> virt/kvm/irqchip.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/virt/kvm/irqchip.c b/virt/kvm/irqchip.c
> index 1e567d1f6d3d..90f54f04e37c 100644
> --- a/virt/kvm/irqchip.c
> +++ b/virt/kvm/irqchip.c
> @@ -216,7 +216,8 @@ int kvm_set_irq_routing(struct kvm *kvm,
> }
>
> mutex_lock(&kvm->irq_lock);
> - old = rcu_dereference_protected(kvm->irq_routing, 1);
> + old = srcu_dereference_check(kvm->irq_routing, &kvm->irq_srcu,
> + lockdep_is_held(&kvm->irq_lock));

Readers of irq_routing are protected via kvm->irq_srcu, but this writer is never
called with kvm->irq_srcu held. I do like the of replacing '1' with
lockdep_is_held(&kvm->irq_lock) to document the protection, so what about just
doing that? I.e.

diff --git a/virt/kvm/irqchip.c b/virt/kvm/irqchip.c
index 1e567d1f6d3d..77a18b4dc103 100644
--- a/virt/kvm/irqchip.c
+++ b/virt/kvm/irqchip.c
@@ -216,7 +216,8 @@ int kvm_set_irq_routing(struct kvm *kvm,
}

mutex_lock(&kvm->irq_lock);
- old = rcu_dereference_protected(kvm->irq_routing, 1);
+ old = rcu_dereference_protected(kvm->irq_routing,
+ lockdep_is_held(&kvm->irq_lock));
rcu_assign_pointer(kvm->irq_routing, new);
kvm_irq_routing_update(kvm);
kvm_arch_irq_routing_update(kvm);

> rcu_assign_pointer(kvm->irq_routing, new);
> kvm_irq_routing_update(kvm);
> kvm_arch_irq_routing_update(kvm);
> --
> 2.27.0