[PATCH] kvm: improve comment on rcu use in irqfd_deassign

[PATCH] kvm: improve comment on rcu use in irqfd_deassign

[Michael S. Tsirkin]

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>
---
 virt/kvm/eventfd.c |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index 2ca4535..3656849 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -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.
 			 */
-- 
1.7.3.2.91.g446ac

Re: [PATCH] kvm: improve comment on rcu use in irqfd_deassign

[Avi Kivity]

On 03/06/2011 01:03 PM, Michael S. Tsirkin wrote:
> 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.

Applied, thanks.

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