KVM: improve comment on rcu use in irqfd_deassign
Michael S. Tsirkin [Sun, 6 Mar 2011 11:03:26 +0000 (13:03 +0200)]
The RCU use in kvm_irqfd_deassign is tricky: we have rcu_assign_pointer
but no synchronize_rcu: synchronize_rcu is done by kvm_irq_routing_update
which we share a spinlock with.

Fix up a comment in an attempt to make this clearer.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

virt/kvm/eventfd.c

index 2ca4535..3656849 100644 (file)
@@ -313,8 +313,9 @@ kvm_irqfd_deassign(struct kvm *kvm, int fd, int gsi)
                if (irqfd->eventfd == eventfd && irqfd->gsi == gsi) {
                        /*
                         * This rcu_assign_pointer is needed for when
-                        * another thread calls kvm_irqfd_update before
-                        * we flush workqueue below.
+                        * another thread calls kvm_irq_routing_update before
+                        * we flush workqueue below (we synchronize with
+                        * kvm_irq_routing_update using irqfds.lock).
                         * It is paired with synchronize_rcu done by caller
                         * of that function.
                         */